V2 reconstruction with client-side optional single range splitting (#703)

This PR introduces V2 multirange URL fetching for xorbs, but optionally
splits the multirange requests into multiple single-range requests that
can be executed in parallel. This allows the reconstruction process to
generate full multirange presigned URLs, but the client effectively
performs the retrieval stage as a sequence of parallel single-range
queries.

The config variable `client.enable_multirange_fetching` controls this
behavior; by default it is set to false due to the current observed
slowness of fetching multiranged URLs.

---------

Co-authored-by: Adrien <adrien@huggingface.co>

api_changes/update_260316_v2_reconstruction_multirange.md

@@ -0,0 +1,94 @@
+# API Update: V2 Reconstruction with Multi-Range Fetch Support (2026-03-16)
+
+## Overview
+
+The CAS reconstruction API now supports a V2 endpoint that returns optimized
+multi-range fetch descriptors.  The client auto-detects V2 and falls back to V1
+transparently.  Two new config options control reconstruction behavior.
+
+---
+
+## 1. New CAS Endpoint
+
+`GET /v2/reconstructions/{file_id}` returns `QueryReconstructionResponseV2`:
+
+```json
+{
+  "terms": [...],
+  "offset_into_first_range": 0,
+  "xorbs": {
+    "<hex_hash>": [
+      {
+        "url": "https://...",
+        "ranges": [
+          { "chunks": { "start": 0, "end": 3 }, "bytes": { "start": 0, "end": 1023 } },
+          { "chunks": { "start": 5, "end": 8 }, "bytes": { "start": 2048, "end": 3071 } }
+        ]
+      }
+    ]
+  }
+}
+```
+
+Each `XorbMultiRangeFetch` entry groups multiple disjoint chunk ranges under a
+single presigned URL, enabling multi-range HTTP requests.
+
+The client tries V2 first.  On 404 or 501 it falls back to V1 and caches the
+result so subsequent calls skip the V2 attempt.  Setting
+`HF_XET_CLIENT_RECONSTRUCTION_API_VERSION=1` or `=2` forces a specific version
+with no fallback.
+
+The `Client::get_reconstruction` trait method now always returns
+`QueryReconstructionResponseV2`.  When the server returns V1, the client
+converts it internally.
+
+---
+
+## 2. New Config Options
+
+### `HF_XET_CLIENT_RECONSTRUCTION_API_VERSION`
+
+Forces a specific reconstruction API version (1 or 2).  When unset, the client
+auto-detects by trying V2 first.
+
+### `HF_XET_CLIENT_ENABLE_MULTIRANGE_FETCHING`
+
+Default: `false`.  When false, V2 multi-range fetch entries are split into
+individual single-range requests executed in parallel.  When true, multi-range
+requests are sent as-is (using `multipart/byteranges` responses).
+
+---
+
+## 3. Default Concurrency Changes
+
+- `ac_initial_upload_concurrency`: 1 → 2
+- `ac_initial_download_concurrency`: 1 → 4
+
+These align the defaults with the documented values.
+
+---
+
+## 4. New Types in `xet_client::cas_types`
+
+- `QueryReconstructionResponseV2` — V2 reconstruction response
+- `XorbMultiRangeFetch` — A presigned URL with associated chunk/byte ranges
+- `XorbRangeDescriptor` — A single chunk range + byte range pair
+
+---
+
+## 5. Multipart/Byteranges Parsing
+
+`xet_client::cas_client::multipart::parse_multipart_byteranges` parses RFC 7233
+`multipart/byteranges` HTTP responses.  Used when `enable_multirange_fetching`
+is true and the presigned URL server returns multiple byte ranges in a single
+response.
+
+---
+
+## 6. Downstream Impact
+
+- `Client::get_reconstruction` return type changed to `QueryReconstructionResponseV2`
+  (all trait implementations updated).
+- `URLProvider::retrieve_url` now returns `Vec<HttpRange>` instead of a single
+  `HttpRange` to support multi-range blocks.
+- No wire format or serialization changes; V1 responses are converted client-side.

openapi/cas.openapi.yaml

@@ -14,24 +14,27 @@ security:
 paths:
   /v1/reconstructions/{file_id}:
     get:
-      summary: Get File Reconstruction
+      summary: Get File Reconstruction (V1)
       description: |
         Retrieves reconstruction information for a specific file. Supports byte range via the optional `Range` header.
+        Returns one presigned URL per chunk range per xorb.
+
         Minimum token scope: `read`.
         x-required-scope: read
-      operationId: getReconstruction
+      operationId: getReconstructionV1
       parameters:
         - $ref: '#/components/parameters/FileIdParam'
         - $ref: '#/components/parameters/RangeHeader'
       responses:
         '200':
-          description: Reconstruction object
+          description: V1 reconstruction object
           content:
             application/json:
               schema:
                 $ref: '#/components/schemas/QueryReconstructionResponse'
               examples:
-                example:
+                v1:
+                  summary: V1 response
                   value:
                     offset_into_first_range: 0
                     terms:
@@ -57,6 +60,60 @@ paths:
           description: Not Found — File does not exist
         '416':
           description: Range Not Satisfiable — Requested byte range start exceeds file length
+  /v2/reconstructions/{file_id}:
+    get:
+      summary: Get File Reconstruction (V2)
+      description: |
+        V2 reconstruction endpoint optimized for multi-range fetching.
+        Returns fewer signed URLs by combining multiple byte ranges for the same xorb into a single URL,
+        enabling multi-range HTTP requests (RFC 7233).
+
+        Clients SHOULD try V2 first and fall back to V1 if the server returns 404 or 501.
+
+        Minimum token scope: `read`.
+        x-required-scope: read
+      operationId: getReconstructionV2
+      parameters:
+        - $ref: '#/components/parameters/FileIdParam'
+        - $ref: '#/components/parameters/RangeHeader'
+      responses:
+        '200':
+          description: V2 reconstruction object
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/QueryReconstructionResponseV2'
+              examples:
+                v2:
+                  summary: V2 response (multi-range optimized)
+                  value:
+                    offset_into_first_range: 0
+                    terms:
+                      - hash: a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456
+                        unpacked_length: 263873
+                        range:
+                          start: 0
+                          end: 4
+                    xorbs:
+                      a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456:
+                        - url: "https://transfer.xethub.hf.co/xorbs/default/a1b2c3...?<signed-params>"
+                          ranges:
+                            - chunks:
+                                start: 0
+                                end: 4
+                              bytes:
+                                start: 0
+                                end: 131071
+        '400':
+          description: Bad Request — Malformed file_id
+        '401':
+          description: Unauthorized — Missing/expired token
+        '404':
+          description: Not Found — File does not exist, or V2 not supported (fall back to V1)
+        '416':
+          description: Range Not Satisfiable — Requested byte range start exceeds file length
+        '501':
+          description: Not Implemented — V2 not supported by this server (fall back to V1)
   /v1/chunks/{prefix}/{hash}:
     get:
       summary: Query Chunk Deduplication (Global Deduplication)
@@ -286,6 +343,56 @@ components:
               $ref: '#/components/schemas/CASReconstructionFetchInfo'
       required: [offset_into_first_range, terms, fetch_info]
       additionalProperties: false
+    XorbRangeDescriptor:
+      type: object
+      description: A chunk/byte range within a xorb
+      properties:
+        chunks:
+          $ref: '#/components/schemas/IndexRange'
+        bytes:
+          $ref: '#/components/schemas/ByteRange'
+      required: [chunks, bytes]
+      additionalProperties: false
+    XorbMultiRangeFetch:
+      type: object
+      description: A signed multi-range fetch entry covering a subset of ranges for a xorb
+      properties:
+        url:
+          type: string
+          format: uri
+          description: |
+            Signed URL with all byte ranges encoded.
+            Client must send exactly the signed range value as the Range header.
+        ranges:
+          type: array
+          items:
+            $ref: '#/components/schemas/XorbRangeDescriptor'
+          description: Byte ranges covered by this URL, sorted by chunk start
+      required: [url, ranges]
+      additionalProperties: false
+    QueryReconstructionResponseV2:
+      type: object
+      description: V2 reconstruction response optimized for multi-range fetching
+      properties:
+        offset_into_first_range:
+          type: integer
+          minimum: 0
+        terms:
+          type: array
+          items:
+            $ref: '#/components/schemas/CASReconstructionTerm'
+        xorbs:
+          type: object
+          description: Map from xorb hash to list of multi-range fetch entries
+          propertyNames:
+            $ref: '#/components/schemas/HexString64Lowercase'
+          additionalProperties:
+            type: array
+            items:
+              $ref: '#/components/schemas/XorbMultiRangeFetch'
+            minItems: 1
+      required: [offset_into_first_range, terms, xorbs]
+      additionalProperties: false
     UploadXorbResponse:
       type: object
       properties:

xet_client/src/cas_client/interface.rs

@@ -6,14 +6,16 @@ use xet_core_structures::xorb_object::SerializedXorbObject;
 use super::adaptive_concurrency::ConnectionPermit;
 use super::error::Result;
 use super::progress_tracked_streams::ProgressCallback;
-use crate::cas_types::{BatchQueryReconstructionResponse, FileRange, HttpRange, QueryReconstructionResponse};
+use crate::cas_types::{BatchQueryReconstructionResponse, FileRange, HttpRange, QueryReconstructionResponseV2};
 
 #[async_trait::async_trait]
 pub trait URLProvider: Send + Sync {
-    // Retrieves the URL.
-    async fn retrieve_url(&self) -> Result<(String, HttpRange)>;
+    /// Retrieves the URL and the byte ranges to fetch.
+    /// For single-range (V1) blocks, the Vec has one entry.
+    /// For multi-range (V2) blocks, all ranges are included.
+    async fn retrieve_url(&self) -> Result<(String, Vec<HttpRange>)>;
 
-    // Asks for a refresh of the URL; triggered on 403 errors.
+    /// Asks for a refresh of the URL; triggered on 403 errors.
     async fn refresh_url(&self) -> Result<()>;
 }
 
@@ -30,11 +32,13 @@ pub trait Client: Send + Sync {
         file_hash: &MerkleHash,
     ) -> Result<Option<(MDBFileInfo, Option<MerkleHash>)>>;
 
+    /// Returns reconstruction info always in V2 format.
+    /// Implementations may try V2 first and fall back to V1 + convert.
     async fn get_reconstruction(
         &self,
         file_id: &MerkleHash,
         bytes_range: Option<FileRange>,
-    ) -> Result<Option<QueryReconstructionResponse>>;
+    ) -> Result<Option<QueryReconstructionResponseV2>>;
 
     async fn batch_get_reconstruction(&self, file_ids: &[MerkleHash]) -> Result<BatchQueryReconstructionResponse>;
 

xet_client/src/cas_client/mod.rs

@@ -16,6 +16,7 @@ mod error;
 pub mod exports;
 pub mod http_client;
 mod interface;
+pub mod multipart;
 pub mod progress_tracked_streams;
 pub mod remote_client;
 pub mod retry_wrapper;

xet_client/src/cas_client/multipart.rs

@@ -0,0 +1,186 @@
+use bytes::Bytes;
+
+use crate::cas_client::error::{CasClientError, Result};
+use crate::cas_types::HttpRange;
+
+/// A single part from a multipart/byteranges HTTP response.
+pub struct MultipartPart {
+    pub range: HttpRange,
+    pub data: Bytes,
+}
+
+/// Parse a `multipart/byteranges` HTTP response body (RFC 7233 §4.1).
+///
+/// Extracts the boundary from `content_type`, splits the body by boundary markers,
+/// parses `Content-Range` headers from each part, and returns parts sorted by byte range start.
+pub fn parse_multipart_byteranges(content_type: &str, body: Bytes) -> Result<Vec<MultipartPart>> {
+    let boundary = extract_boundary(content_type)?;
+
+    let delimiter = format!("\r\n--{boundary}");
+    let body_slice = body.as_ref();
+
+    let mut parts = Vec::new();
+
+    let first_delim = format!("--{boundary}");
+    let Some(start) = find_subsequence(body_slice, first_delim.as_bytes()) else {
+        return Err(CasClientError::Other("No boundary found in multipart body".to_string()));
+    };
+
+    let mut remaining = &body_slice[start + first_delim.len()..];
+
+    loop {
+        if remaining.starts_with(b"\r\n") {
+            remaining = &remaining[2..];
+        } else {
+            break;
+        }
+
+        let next_boundary = find_subsequence(remaining, delimiter.as_bytes());
+        let part_data = match next_boundary {
+            Some(pos) => &remaining[..pos],
+            None => remaining,
+        };
+
+        let Some(header_end) = find_subsequence(part_data, b"\r\n\r\n") else {
+            return Err(CasClientError::Other("Malformed multipart part: missing header/data separator".to_string()));
+        };
+
+        let headers = &part_data[..header_end];
+        let data_start = header_end + 4;
+        let data = &part_data[data_start..];
+
+        let range = parse_content_range(headers)?;
+        // Compute the absolute byte offset into the original `body` so we can
+        // use Bytes::slice for zero-copy extraction of this part's data.
+        let offset =
+            body.len() - body_slice.len() + (remaining.as_ptr() as usize - body_slice.as_ptr() as usize) + data_start;
+        parts.push(MultipartPart {
+            range,
+            data: body.slice(offset..offset + data.len()),
+        });
+
+        match next_boundary {
+            Some(pos) => {
+                remaining = &remaining[pos + delimiter.len()..];
+            },
+            None => break,
+        }
+    }
+
+    parts.sort_by_key(|p| p.range.start);
+
+    Ok(parts)
+}
+
+fn extract_boundary(content_type: &str) -> Result<String> {
+    for part in content_type.split(';') {
+        let part = part.trim();
+        if let Some(value) = part.strip_prefix("boundary=") {
+            let boundary = value.trim_matches('"');
+            return Ok(boundary.to_string());
+        }
+    }
+    Err(CasClientError::Other(format!("No boundary found in Content-Type: {content_type}")))
+}
+
+fn parse_content_range(headers: &[u8]) -> Result<HttpRange> {
+    let headers_str = std::str::from_utf8(headers)
+        .map_err(|e| CasClientError::Other(format!("Invalid UTF-8 in part headers: {e}")))?;
+
+    for line in headers_str.split("\r\n") {
+        let line_lower = line.to_ascii_lowercase();
+        if let Some(value) = line_lower.strip_prefix("content-range:") {
+            // Digits, dashes, and slashes are case-invariant, so we can parse
+            // directly from the lowercased value.
+            if let Some(range_spec) = value.trim().strip_prefix("bytes ") {
+                let original_value = range_spec.trim();
+                let slash_pos = original_value
+                    .find('/')
+                    .ok_or_else(|| CasClientError::Other(format!("Invalid Content-Range: {line}")))?;
+                let range_part = &original_value[..slash_pos];
+                let dash_pos = range_part
+                    .find('-')
+                    .ok_or_else(|| CasClientError::Other(format!("Invalid Content-Range: {line}")))?;
+                let start: u64 = range_part[..dash_pos]
+                    .parse()
+                    .map_err(|e| CasClientError::Other(format!("Invalid Content-Range start: {e}")))?;
+                let end: u64 = range_part[dash_pos + 1..]
+                    .parse()
+                    .map_err(|e| CasClientError::Other(format!("Invalid Content-Range end: {e}")))?;
+                // RFC 7233 Content-Range uses an inclusive end, which matches HttpRange.
+                return Ok(HttpRange::new(start, end));
+            }
+        }
+    }
+
+    Err(CasClientError::Other("No Content-Range header found in multipart part".to_string()))
+}
+
+fn find_subsequence(haystack: &[u8], needle: &[u8]) -> Option<usize> {
+    haystack.windows(needle.len()).position(|window| window == needle)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_extract_boundary() {
+        assert_eq!(extract_boundary("multipart/byteranges; boundary=something").unwrap(), "something");
+        assert_eq!(extract_boundary("multipart/byteranges; boundary=\"quoted\"").unwrap(), "quoted");
+    }
+
+    #[test]
+    fn test_extract_boundary_missing() {
+        assert!(extract_boundary("text/plain").is_err());
+    }
+
+    #[test]
+    fn test_parse_single_part() {
+        let boundary = "abc123";
+        let body = format!(
+            "--{boundary}\r\nContent-Type: application/octet-stream\r\nContent-Range: bytes 0-99/1000\r\n\r\nHello World\r\n--{boundary}--\r\n"
+        );
+        let content_type = format!("multipart/byteranges; boundary={boundary}");
+
+        let parts = parse_multipart_byteranges(&content_type, Bytes::from(body)).unwrap();
+        assert_eq!(parts.len(), 1);
+        assert_eq!(parts[0].range.start, 0);
+        assert_eq!(parts[0].range.end, 99);
+        assert_eq!(&parts[0].data[..], b"Hello World");
+    }
+
+    #[test]
+    fn test_parse_multiple_parts() {
+        let boundary = "sep";
+        let body = format!(
+            "--{boundary}\r\nContent-Range: bytes 100-199/1000\r\n\r\nPart2Data\r\n--{boundary}\r\nContent-Range: bytes 0-49/1000\r\n\r\nPart1Data\r\n--{boundary}--\r\n"
+        );
+        let content_type = format!("multipart/byteranges; boundary={boundary}");
+
+        let parts = parse_multipart_byteranges(&content_type, Bytes::from(body)).unwrap();
+        assert_eq!(parts.len(), 2);
+        assert_eq!(parts[0].range.start, 0);
+        assert_eq!(parts[0].range.end, 49);
+        assert_eq!(&parts[0].data[..], b"Part1Data");
+        assert_eq!(parts[1].range.start, 100);
+        assert_eq!(parts[1].range.end, 199);
+        assert_eq!(&parts[1].data[..], b"Part2Data");
+    }
+
+    #[test]
+    fn test_parse_empty_body_no_boundary() {
+        let content_type = "multipart/byteranges; boundary=xyz";
+        let result = parse_multipart_byteranges(content_type, Bytes::new());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_parse_part_missing_header_separator() {
+        let boundary = "xyz";
+        let body = format!("--{boundary}\r\nContent-Range: bytes 0-9/100\r\nMISSING_SEPARATOR\r\n--{boundary}--\r\n");
+        let content_type = format!("multipart/byteranges; boundary={boundary}");
+        let result = parse_multipart_byteranges(&content_type, Bytes::from(body));
+        assert!(result.is_err());
+    }
+}

xet_client/src/cas_client/remote_client.rs

@@ -1,5 +1,5 @@
 use std::sync::Arc;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicU32, AtomicU64, Ordering};
 
 use bytes::Bytes;
 use futures::TryStreamExt;
@@ -24,8 +24,8 @@ use super::progress_tracked_streams::{
 use super::retry_wrapper::{RetryWrapper, RetryableReqwestError};
 use super::{Client, INFORMATION_LOG_LEVEL};
 use crate::cas_types::{
-    BatchQueryReconstructionResponse, FileRange, HttpRange, Key, QueryReconstructionResponse, UploadShardResponse,
-    UploadShardResponseType, UploadXorbResponse,
+    BatchQueryReconstructionResponse, FileRange, HttpRange, Key, QueryReconstructionResponse,
+    QueryReconstructionResponseV2, UploadShardResponse, UploadShardResponseType, UploadXorbResponse,
 };
 
 pub const CAS_ENDPOINT: &str = "http://localhost:8080";
@@ -48,6 +48,8 @@ pub struct RemoteClient {
     shard_upload_http_client: Arc<ClientWithMiddleware>,
     upload_concurrency_controller: Arc<AdaptiveConcurrencyController>,
     download_concurrency_controller: Arc<AdaptiveConcurrencyController>,
+    /// Caches the discovered reconstruction API version (0 = not yet probed, 1 = V1, 2 = V2).
+    detected_reconstruction_api_version: AtomicU32,
 }
 
 impl RemoteClient {
@@ -85,6 +87,7 @@ impl RemoteClient {
             ),
             upload_concurrency_controller: AdaptiveConcurrencyController::new_upload("upload"),
             download_concurrency_controller: AdaptiveConcurrencyController::new_download("download"),
+            detected_reconstruction_api_version: AtomicU32::new(0),
         })
     }
 
@@ -168,6 +171,126 @@ impl RemoteClient {
     }
 }
 
+impl RemoteClient {
+    async fn get_reconstruction_impl<T>(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+        api_version: &str,
+    ) -> Result<Option<T>>
+    where
+        T: serde::de::DeserializeOwned + 'static,
+    {
+        let call_id = FN_CALL_ID.fetch_add(1, Ordering::Relaxed);
+        let url = Url::parse(&format!("{}/{api_version}/reconstructions/{}", self.endpoint, file_id.hex()))?;
+        let api_tag = match api_version {
+            "v1" => "cas::get_reconstruction_v1",
+            "v2" => "cas::get_reconstruction_v2",
+            _ => {
+                return Err(CasClientError::internal(format!("unsupported reconstruction API version: {api_version}")));
+            },
+        };
+
+        event!(
+            INFORMATION_LOG_LEVEL,
+            call_id,
+            %file_id,
+            ?bytes_range,
+            api_version,
+            "Starting get_reconstruction API call",
+        );
+
+        let client = self.authenticated_http_client.clone();
+
+        let result: Result<T> = RetryWrapper::new(api_tag)
+            .run_and_extract_json(move || {
+                let mut request = client.get(url.clone()).with_extension(Api(api_tag));
+                if let Some(range) = bytes_range {
+                    request = request.header(RANGE, HttpRange::from(range).range_header())
+                }
+                request.send()
+            })
+            .await;
+
+        match result {
+            Ok(response) => {
+                event!(
+                    INFORMATION_LOG_LEVEL,
+                    call_id,
+                    %file_id,
+                    ?bytes_range,
+                    api_version,
+                    "Completed get_reconstruction API call"
+                );
+                Ok(Some(response))
+            },
+            Err(CasClientError::ReqwestError(ref e, _)) if e.status() == Some(StatusCode::RANGE_NOT_SATISFIABLE) => {
+                Ok(None)
+            },
+            Err(e) => Err(e),
+        }
+    }
+
+    /// V1 reconstruction: returns per-range presigned URLs.
+    pub async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponse>> {
+        self.get_reconstruction_impl(file_id, bytes_range, "v1").await
+    }
+
+    /// V2 reconstruction: returns per-xorb multi-range fetch descriptors.
+    pub async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        self.get_reconstruction_impl(file_id, bytes_range, "v2").await
+    }
+
+    pub(crate) async fn get_reconstruction_with_version_override(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+        forced_version: Option<u32>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        // Prefer V2; fall back to V1 on 404/501; persist detected version to
+        // avoid repeated fallback attempts.
+        let version = match forced_version {
+            Some(v) => v,
+            None => {
+                let detected = self.detected_reconstruction_api_version.load(Ordering::Relaxed);
+                if detected != 0 { detected } else { 2 }
+            },
+        };
+
+        match version {
+            2 => match self.get_reconstruction_v2(file_id, bytes_range).await {
+                Ok(result) => {
+                    if forced_version.is_none() {
+                        self.detected_reconstruction_api_version.store(2, Ordering::Relaxed);
+                    }
+                    Ok(result)
+                },
+                Err(e)
+                    if forced_version.is_none()
+                        && matches!(e.status(), Some(StatusCode::NOT_FOUND) | Some(StatusCode::NOT_IMPLEMENTED)) =>
+                {
+                    info!(status = ?e.status(), "V2 reconstruction not available, falling back to V1");
+                    let result = self.get_reconstruction_v1(file_id, bytes_range).await?.map(Into::into);
+                    // Store after success to make sure we don't mess up on e.g. network failure.
+                    self.detected_reconstruction_api_version.store(1, Ordering::Relaxed);
+                    Ok(result)
+                },
+                Err(e) => Err(e),
+            },
+            1 => Ok(self.get_reconstruction_v1(file_id, bytes_range).await?.map(Into::into)),
+            other => Err(CasClientError::internal(format!("unsupported reconstruction API version: {other}"))),
+        }
+    }
+}
+
 #[cfg_attr(not(target_family = "wasm"), async_trait::async_trait)]
 #[cfg_attr(target_family = "wasm", async_trait::async_trait(?Send))]
 impl Client for RemoteClient {
@@ -175,49 +298,10 @@ impl Client for RemoteClient {
         &self,
         file_id: &MerkleHash,
         bytes_range: Option<FileRange>,
-    ) -> Result<Option<QueryReconstructionResponse>> {
-        let call_id = FN_CALL_ID.fetch_add(1, Ordering::Relaxed);
-        let url = Url::parse(&format!("{}/v1/reconstructions/{}", self.endpoint, file_id.hex()))?;
-        event!(
-            INFORMATION_LOG_LEVEL,
-            call_id,
-            %file_id,
-            ?bytes_range,
-            "Starting get_reconstruction API call",
-        );
-
-        let api_tag = "cas::get_reconstruction";
-        let client = self.authenticated_http_client.clone();
-
-        let result: Result<QueryReconstructionResponse> = RetryWrapper::new(api_tag)
-            .run_and_extract_json(move || {
-                let mut request = client.get(url.clone()).with_extension(Api(api_tag));
-                if let Some(range) = bytes_range {
-                    // convert exclusive-end to inclusive-end range
-                    request = request.header(RANGE, HttpRange::from(range).range_header())
-                }
-
-                request.send()
-            })
-            .await;
-
-        match result {
-            Ok(query_reconstruction_response) => {
-                event!(
-                    INFORMATION_LOG_LEVEL,
-                    call_id,
-                    %file_id,
-                    ?bytes_range,
-                    "Completed get_reconstruction API call"
-                );
-                Ok(Some(query_reconstruction_response))
-            },
-            Err(CasClientError::ReqwestError(ref e, _)) if e.status() == Some(StatusCode::RANGE_NOT_SATISFIABLE) => {
-                // bytes_range not satisfiable
-                Ok(None)
-            },
-            Err(e) => Err(e),
-        }
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        let forced_version = xet_config().client.reconstruction_api_version;
+        self.get_reconstruction_with_version_override(file_id, bytes_range, forced_version)
+            .await
     }
 
     async fn batch_get_reconstruction(&self, file_ids: &[MerkleHash]) -> Result<BatchQueryReconstructionResponse> {
@@ -270,8 +354,8 @@ impl Client for RemoteClient {
         let http_client = self.http_client.clone();
         let url_info = Arc::new(url_info);
 
-        let (_, url_range) = url_info.retrieve_url().await?;
-        let total_download_bytes = url_range.length();
+        let (_, url_ranges) = url_info.retrieve_url().await?;
+        let total_download_bytes: u64 = url_ranges.iter().map(|r| r.length()).sum();
 
         let mut transfer_reporter = StreamProgressReporter::new(total_download_bytes)
             .with_adaptive_concurrency_reporter(download_permit.get_partial_completion_reporting_function());
@@ -288,16 +372,28 @@ impl Client for RemoteClient {
                     let url_info = url_info.clone();
 
                     async move {
-                        let (url_string, url_range) = url_info
+                        let (url_string, url_ranges) = url_info
                             .retrieve_url()
                             .await
                             .map_err(|e| reqwest_middleware::Error::Middleware(e.into()))?;
                         let url =
                             Url::parse(&url_string).map_err(|e| reqwest_middleware::Error::Middleware(e.into()))?;
 
+                        // RFC 7233 §2.1: single-range uses "bytes=S-E", multi-range uses "bytes=S1-E1,S2-E2,..."
+                        let range_header_value = if url_ranges.len() == 1 {
+                            url_ranges[0].range_header()
+                        } else {
+                            let joined = url_ranges
+                                .iter()
+                                .map(|r| format!("{}-{}", r.start, r.end))
+                                .collect::<Vec<_>>()
+                                .join(",");
+                            format!("bytes={joined}")
+                        };
+
                         let response = http_client
                             .get(url)
-                            .header(RANGE, url_range.range_header())
+                            .header(RANGE, range_header_value)
                             .with_extension(Api(api_tag))
                             .send()
                             .await?;
@@ -315,6 +411,57 @@ impl Client for RemoteClient {
                 move |resp: Response| {
                     let transfer_reporter = transfer_reporter.clone();
                     async move {
+                        let content_type = resp
+                            .headers()
+                            .get("content-type")
+                            .and_then(|v| v.to_str().ok())
+                            .unwrap_or("")
+                            .to_string();
+
+                        let is_multipart = content_type.contains("multipart/byteranges");
+
+                        if is_multipart {
+                            let body = resp
+                                .bytes()
+                                .await
+                                .map_err(|e| RetryableReqwestError::RetryableError(CasClientError::from(e)))?;
+
+                            let multipart_parts = crate::cas_client::multipart::parse_multipart_byteranges(&content_type, body)
+                                .map_err(RetryableReqwestError::FatalError)?;
+
+                            let mut all_decompressed = Vec::with_capacity(uncompressed_size_if_known.unwrap_or(0));
+                            let mut all_chunk_indices = Vec::<u32>::new();
+                            let mut total_compressed_bytes = 0u64;
+
+                            for part in multipart_parts {
+                                total_compressed_bytes += part.data.len() as u64;
+
+                                let (data, chunk_indices) =
+                                    xet_core_structures::xorb_object::deserialize_chunks(&mut std::io::Cursor::new(part.data.as_ref()))
+                                        .map_err(|e| {
+                                            RetryableReqwestError::RetryableError(CasClientError::FormatError(e))
+                                        })?;
+
+                                xet_core_structures::xorb_object::append_chunk_segment(
+                                    &mut all_decompressed,
+                                    &mut all_chunk_indices,
+                                    &data,
+                                    &chunk_indices,
+                                );
+
+                                transfer_reporter.report_progress(total_compressed_bytes as usize);
+                            }
+
+                            if let Some(expected) = uncompressed_size_if_known
+                                && expected != all_decompressed.len()
+                            {
+                                return Err(RetryableReqwestError::RetryableError(CasClientError::Other(format!(
+                                    "get_file_term_data: expected {expected} uncompressed bytes, got {}",
+                                    all_decompressed.len()
+                                ))));
+                            }
+                            Ok((Bytes::from(all_decompressed), all_chunk_indices))
+                        } else {
                             let incoming_stream = DownloadProgressStream::wrap_stream(
                                 resp.bytes_stream().map_err(std::io::Error::other),
                                 transfer_reporter,
@@ -345,6 +492,7 @@ impl Client for RemoteClient {
                                 Err(e) => Err(RetryableReqwestError::RetryableError(CasClientError::FormatError(e))),
                             }
                         }
+                    }
                 },
             )
             .await?;

xet_client/src/cas_client/retry_wrapper.rs

@@ -157,10 +157,13 @@ impl RetryWrapper {
                 }
             },
             (Err(e), Some(Retryable::Transient)) => {
-                // Intercept the too many requests condition in the case of no retrying on 429.
                 if e.status() == Some(StatusCode::TOO_MANY_REQUESTS) && self.no_retry_on_429 {
                     let cas_err = process_error("Too Many Requests (retry on 429 disabled)", e, false);
                     Err(RetryableReqwestError::FatalError(cas_err))
+                } else if e.status() == Some(StatusCode::NOT_IMPLEMENTED) {
+                    // 501 is permanent -- the server won't implement this on retry.
+                    let cas_err = process_error("Not Implemented", e, true);
+                    Err(RetryableReqwestError::FatalError(cas_err))
                 } else {
                     let cas_err = process_error("Retryable Error", e, true);
                     Err(RetryableReqwestError::RetryableError(cas_err))

xet_client/src/cas_client/simulation/client_unit_testing.rs

@@ -36,6 +36,11 @@ where
     test_get_file_data_with_ranges(factory().await).await;
     test_get_file_size(factory().await).await;
     test_global_dedup(factory().await).await;
+    test_v2_reconstruction_basic(factory().await).await;
+    test_v2_reconstruction_ranges(factory().await).await;
+    test_v2_reconstruction_matches_v1(factory().await).await;
+    test_v2_max_ranges_per_fetch(factory().await).await;
+    test_v2_url_encoding(factory().await).await;
 }
 
 /// Tests that adjacent chunk ranges from the same xorb are merged into a single fetch_info.
@@ -43,7 +48,7 @@ pub async fn test_reconstruction_merges_adjacent_ranges(client: Arc<dyn DirectAc
     let term_spec = &[(1, (0, 2)), (1, (2, 4))];
     let file = client.upload_random_file(term_spec, 2048).await.unwrap();
 
-    let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
     assert_eq!(reconstruction.terms.len(), 2);
     assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -59,7 +64,7 @@ pub async fn test_reconstruction_with_multiple_xorbs(client: Arc<dyn DirectAcces
     let term_spec = &[(1, (0, 3)), (2, (0, 2)), (1, (3, 5))];
     let file = client.upload_random_file(term_spec, 2048).await.unwrap();
 
-    let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
     assert_eq!(reconstruction.terms.len(), 3);
     assert_eq!(reconstruction.fetch_info.len(), 2);
 }
@@ -73,7 +78,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (0, 3)), (1, (1, 4))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 2);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -89,7 +94,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (0, 5)), (1, (1, 3))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 2);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -105,7 +110,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (0, 2)), (1, (1, 4)), (1, (3, 6))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 3);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -121,7 +126,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (0, 2)), (1, (4, 6))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 2);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -139,7 +144,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (0, 3)), (1, (3, 5))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 2);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -155,7 +160,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (2, 5)), (1, (2, 5)), (1, (2, 5))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 3);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -171,7 +176,7 @@ pub async fn test_reconstruction_overlapping_range_merging(client: Arc<dyn Direc
         let term_spec = &[(1, (0, 3)), (1, (2, 4)), (1, (6, 8)), (1, (7, 10))];
         let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 4);
         assert_eq!(reconstruction.fetch_info.len(), 1);
 
@@ -191,12 +196,12 @@ pub async fn test_range_requests(client: Arc<dyn DirectAccessClient>) {
     let file = client.upload_random_file(term_spec, 2048).await.unwrap();
 
     // Calculate total file size from terms
-    let reconstruction_full = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction_full = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
     let total_file_size: u64 = reconstruction_full.terms.iter().map(|t| t.unpacked_length as u64).sum();
 
     // Partial out-of-range truncates
     let response = client
-        .get_reconstruction(&file.file_hash, Some(FileRange::new(total_file_size / 2, total_file_size + 1000)))
+        .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(total_file_size / 2, total_file_size + 1000)))
         .await
         .unwrap()
         .unwrap();
@@ -205,19 +210,19 @@ pub async fn test_range_requests(client: Arc<dyn DirectAccessClient>) {
 
     // Entire range out of bounds returns Ok(None) (like RemoteClient's 416 handling)
     let result = client
-        .get_reconstruction(&file.file_hash, Some(FileRange::new(total_file_size + 100, total_file_size + 1000)))
+        .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(total_file_size + 100, total_file_size + 1000)))
         .await;
     assert!(result.unwrap().is_none());
 
     // Start equals file size returns Ok(None)
     let result = client
-        .get_reconstruction(&file.file_hash, Some(FileRange::new(total_file_size, total_file_size + 100)))
+        .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(total_file_size, total_file_size + 100)))
         .await;
     assert!(result.unwrap().is_none());
 
     // Valid range within bounds succeeds
     let response = client
-        .get_reconstruction(&file.file_hash, Some(FileRange::new(0, total_file_size / 2)))
+        .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(0, total_file_size / 2)))
         .await
         .unwrap()
         .unwrap();
@@ -226,7 +231,7 @@ pub async fn test_range_requests(client: Arc<dyn DirectAccessClient>) {
 
     // End exactly at file size succeeds
     let response = client
-        .get_reconstruction(&file.file_hash, Some(FileRange::new(0, total_file_size)))
+        .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(0, total_file_size)))
         .await
         .unwrap()
         .unwrap();
@@ -239,7 +244,7 @@ pub async fn test_upload_configurations(client: Arc<dyn DirectAccessClient>) {
     // Test 1: Single segment with 3 chunks
     {
         let file = client.upload_random_file(&[(1, (0, 3))], 2048).await.unwrap();
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 1);
     }
 
@@ -248,7 +253,7 @@ pub async fn test_upload_configurations(client: Arc<dyn DirectAccessClient>) {
         let term_spec = &[(1, (0, 2)), (1, (2, 4)), (1, (4, 6))];
         let file = client.upload_random_file(term_spec, 2048).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 3);
         assert_eq!(reconstruction.fetch_info.len(), 1);
     }
@@ -258,7 +263,7 @@ pub async fn test_upload_configurations(client: Arc<dyn DirectAccessClient>) {
         let term_spec = &[(1, (0, 3)), (2, (0, 2)), (3, (0, 4))];
         let file = client.upload_random_file(term_spec, 2048).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 3);
         assert_eq!(reconstruction.fetch_info.len(), 3);
     }
@@ -268,7 +273,7 @@ pub async fn test_upload_configurations(client: Arc<dyn DirectAccessClient>) {
         let term_spec = &[(1, (0, 3)), (1, (1, 4)), (1, (2, 5))];
         let file = client.upload_random_file(term_spec, 2048).await.unwrap();
 
-        let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+        let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
         assert_eq!(reconstruction.terms.len(), 3);
         assert_eq!(reconstruction.fetch_info.len(), 1);
     }
@@ -280,7 +285,7 @@ pub async fn test_chunk_boundary_shrinking(client: Arc<dyn DirectAccessClient>)
     let term_spec = &[(1, (0, 5))];
     let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-    let reconstruction_full = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction_full = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
     let total_file_size: u64 = reconstruction_full.terms.iter().map(|t| t.unpacked_length as u64).sum();
     assert_eq!(total_file_size, (5 * chunk_size) as u64);
 
@@ -289,7 +294,7 @@ pub async fn test_chunk_boundary_shrinking(client: Arc<dyn DirectAccessClient>)
         let start = chunk_size as u64 + 500;
         let end = total_file_size;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -305,7 +310,7 @@ pub async fn test_chunk_boundary_shrinking(client: Arc<dyn DirectAccessClient>)
         let start = (chunk_size * 2) as u64;
         let end = total_file_size;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -321,7 +326,7 @@ pub async fn test_chunk_boundary_shrinking(client: Arc<dyn DirectAccessClient>)
         let start = 0u64;
         let end = (chunk_size * 2) as u64 + 500;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -337,7 +342,7 @@ pub async fn test_chunk_boundary_shrinking(client: Arc<dyn DirectAccessClient>)
         let start = (chunk_size * 2) as u64 + 100;
         let end = (chunk_size * 2) as u64 + 500;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -353,7 +358,7 @@ pub async fn test_chunk_boundary_shrinking(client: Arc<dyn DirectAccessClient>)
         let start = chunk_size as u64 - 100;
         let end = chunk_size as u64 + 100;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -371,7 +376,7 @@ pub async fn test_chunk_boundary_multiple_segments(client: Arc<dyn DirectAccessC
     let term_spec = &[(1, (0, 4)), (2, (0, 4))];
     let file = client.upload_random_file(term_spec, chunk_size).await.unwrap();
 
-    let reconstruction_full = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction_full = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
     let total_file_size: u64 = reconstruction_full.terms.iter().map(|t| t.unpacked_length as u64).sum();
     assert_eq!(total_file_size, (8 * chunk_size) as u64);
 
@@ -380,7 +385,7 @@ pub async fn test_chunk_boundary_multiple_segments(client: Arc<dyn DirectAccessC
         let start = chunk_size as u64 + 500;
         let end = total_file_size;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -398,7 +403,7 @@ pub async fn test_chunk_boundary_multiple_segments(client: Arc<dyn DirectAccessC
         let start = chunk_size as u64;
         let end = (chunk_size * 3) as u64;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -415,7 +420,7 @@ pub async fn test_chunk_boundary_multiple_segments(client: Arc<dyn DirectAccessC
         let start = xorb1_size + chunk_size as u64;
         let end = xorb1_size + (chunk_size * 3) as u64;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -432,7 +437,7 @@ pub async fn test_chunk_boundary_multiple_segments(client: Arc<dyn DirectAccessC
         let start = (chunk_size * 2) as u64;
         let end = xorb1_size + (chunk_size * 2) as u64 + 500;
         let response = client
-            .get_reconstruction(&file.file_hash, Some(FileRange::new(start, end)))
+            .get_reconstruction_v1(&file.file_hash, Some(FileRange::new(start, end)))
             .await
             .unwrap()
             .unwrap();
@@ -712,7 +717,7 @@ async fn test_url_expiration_within_window(client: Arc<dyn DirectAccessClient>)
 
     // Upload a file and get reconstruction info (which creates URLs with current timestamp)
     let file = client.upload_random_file(&[(1, (0, 3))], 2048).await.unwrap();
-    let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
 
     // Get the fetch_info for the first term's xorb
     let xorb_hash = file.terms[0].xorb_hash;
@@ -738,7 +743,7 @@ async fn test_url_expiration_after_window(client: Arc<dyn DirectAccessClient>) {
 
     // Upload a file and get reconstruction info (which creates URLs with current timestamp)
     let file = client.upload_random_file(&[(1, (0, 3))], 2048).await.unwrap();
-    let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
 
     // Get the fetch_info for the first term's xorb
     let xorb_hash = file.terms[0].xorb_hash;
@@ -764,7 +769,7 @@ async fn test_url_expiration_default_infinite(client: Arc<dyn DirectAccessClient
 
     // Upload a file and get reconstruction info
     let file = client.upload_random_file(&[(1, (0, 3))], 2048).await.unwrap();
-    let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
 
     // Get the fetch_info for the first term's xorb
     let xorb_hash = file.terms[0].xorb_hash;
@@ -790,7 +795,7 @@ async fn test_url_expiration_exact_boundary(client: Arc<dyn DirectAccessClient>)
 
     // Upload a file and get reconstruction info
     let file = client.upload_random_file(&[(1, (0, 3))], 2048).await.unwrap();
-    let reconstruction = client.get_reconstruction(&file.file_hash, None).await.unwrap().unwrap();
+    let reconstruction = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
 
     // Get the fetch_info for the first term's xorb
     let xorb_hash = file.terms[0].xorb_hash;
@@ -916,3 +921,190 @@ async fn test_api_delay_can_be_disabled(client: Arc<dyn DirectAccessClient>) {
         "Delay should not be applied after disabling: elapsed={elapsed:?}"
     );
 }
+
+// ===== V2 Reconstruction Tests =====
+
+/// Tests basic V2 reconstruction response structure.
+async fn test_v2_reconstruction_basic(client: Arc<dyn DirectAccessClient>) {
+    let term_spec = &[(1, (0, 5))];
+    let file = client.upload_random_file(term_spec, 2048).await.unwrap();
+
+    let response = client.get_reconstruction_v2(&file.file_hash, None).await.unwrap().unwrap();
+
+    assert!(!response.terms.is_empty());
+    assert!(!response.xorbs.is_empty());
+    assert_eq!(response.offset_into_first_range, 0);
+
+    for term in &response.terms {
+        let xorb_descriptor = response.xorbs.get(&term.hash).expect("xorb descriptor missing for term");
+        assert!(!xorb_descriptor.is_empty());
+        for fetch in xorb_descriptor {
+            assert!(!fetch.url.is_empty());
+            assert!(!fetch.ranges.is_empty());
+            for range in &fetch.ranges {
+                assert!(range.bytes.start < range.bytes.end);
+                assert!(range.chunks.start < range.chunks.end);
+            }
+        }
+    }
+}
+
+/// Tests V2 reconstruction with byte range queries.
+async fn test_v2_reconstruction_ranges(client: Arc<dyn DirectAccessClient>) {
+    let term_spec = &[(1, (0, 3)), (2, (0, 3)), (1, (3, 6))];
+    let file = client.upload_random_file(term_spec, 2048).await.unwrap();
+
+    let file_size = file.data.len() as u64;
+
+    // Partial range
+    let range = FileRange::new(file_size / 4, file_size * 3 / 4);
+    let response = client
+        .get_reconstruction_v2(&file.file_hash, Some(range))
+        .await
+        .unwrap()
+        .unwrap();
+
+    assert!(!response.terms.is_empty());
+    assert!(!response.xorbs.is_empty());
+
+    // Out-of-range query returns None
+    let out_of_range = FileRange::new(file_size + 100, file_size + 200);
+    let none_result = client.get_reconstruction_v2(&file.file_hash, Some(out_of_range)).await.unwrap();
+    assert!(none_result.is_none());
+}
+
+/// Tests that V2 reconstruction terms match V1 terms and offsets.
+async fn test_v2_reconstruction_matches_v1(client: Arc<dyn DirectAccessClient>) {
+    let term_spec = &[(1, (0, 3)), (2, (0, 2)), (1, (3, 5))];
+    let file = client.upload_random_file(term_spec, 2048).await.unwrap();
+
+    let v1 = client.get_reconstruction_v1(&file.file_hash, None).await.unwrap().unwrap();
+    let v2 = client.get_reconstruction_v2(&file.file_hash, None).await.unwrap().unwrap();
+
+    assert_eq!(v1.offset_into_first_range, v2.offset_into_first_range);
+    assert_eq!(v1.terms.len(), v2.terms.len());
+    for (t1, t2) in v1.terms.iter().zip(v2.terms.iter()) {
+        assert_eq!(t1.hash, t2.hash);
+        assert_eq!(t1.range, t2.range);
+        assert_eq!(t1.unpacked_length, t2.unpacked_length);
+    }
+
+    // Both should have the same xorb hashes
+    let mut v1_xorb_hashes: Vec<_> = v1.fetch_info.keys().map(|h| h.to_string()).collect();
+    let mut v2_xorb_hashes: Vec<_> = v2.xorbs.keys().map(|h| h.to_string()).collect();
+    v1_xorb_hashes.sort();
+    v2_xorb_hashes.sort();
+    assert_eq!(v1_xorb_hashes, v2_xorb_hashes);
+
+    // Check range with partial file
+    let file_size = file.data.len() as u64;
+    let range = FileRange::new(file_size / 4, file_size * 3 / 4);
+    let v1r = client
+        .get_reconstruction_v1(&file.file_hash, Some(range))
+        .await
+        .unwrap()
+        .unwrap();
+    let v2r = client
+        .get_reconstruction_v2(&file.file_hash, Some(range))
+        .await
+        .unwrap()
+        .unwrap();
+    assert_eq!(v1r.offset_into_first_range, v2r.offset_into_first_range);
+    assert_eq!(v1r.terms.len(), v2r.terms.len());
+}
+
+/// Tests that max_ranges_per_fetch correctly splits multi-range fetch entries.
+async fn test_v2_max_ranges_per_fetch(client: Arc<dyn DirectAccessClient>) {
+    // Use a file with many non-contiguous segments from the same xorb,
+    // interleaved with another xorb to prevent merging.
+    let term_spec = &[
+        (1, (0, 2)),
+        (2, (0, 1)),
+        (1, (2, 4)),
+        (2, (1, 2)),
+        (1, (4, 6)),
+        (2, (2, 3)),
+        (1, (6, 8)),
+    ];
+    let file = client.upload_random_file(term_spec, 512).await.unwrap();
+
+    // Without limit, xorb 1 should have all its ranges in a single fetch
+    let response_unlimited = client.get_reconstruction_v2(&file.file_hash, None).await.unwrap().unwrap();
+
+    // Find xorb 1's descriptor
+    let xorb1_hash = &file.terms[0].xorb_hash;
+    let hex_hash: crate::cas_types::HexMerkleHash = (*xorb1_hash).into();
+    let desc_unlimited = response_unlimited.xorbs.get(&hex_hash).unwrap();
+
+    // Now set max_ranges_per_fetch to 2
+    client.set_max_ranges_per_fetch(2);
+
+    let response_limited = client.get_reconstruction_v2(&file.file_hash, None).await.unwrap().unwrap();
+
+    let desc_limited = response_limited.xorbs.get(&hex_hash).unwrap();
+
+    // With a limit of 2, the number of fetch entries should be >= the unlimited count
+    assert!(
+        desc_limited.len() >= desc_unlimited.len(),
+        "Limited ({}) should have at least as many fetch entries as unlimited ({})",
+        desc_limited.len(),
+        desc_unlimited.len()
+    );
+
+    // Each fetch entry should have at most 2 ranges
+    for fetch in desc_limited {
+        assert!(fetch.ranges.len() <= 2, "Expected at most 2 ranges per fetch, got {}", fetch.ranges.len());
+    }
+
+    // Total ranges across all fetches should equal the unlimited total
+    let total_unlimited: usize = desc_unlimited.iter().map(|f| f.ranges.len()).sum();
+    let total_limited: usize = desc_limited.iter().map(|f| f.ranges.len()).sum();
+    assert_eq!(total_unlimited, total_limited, "Total ranges should be preserved");
+
+    // Reset for other tests
+    client.set_max_ranges_per_fetch(usize::MAX);
+}
+
+/// Tests that V2 URLs are valid base64 and decode correctly.
+/// When going through a server, URLs are HTTP; when direct, they're base64.
+async fn test_v2_url_encoding(client: Arc<dyn DirectAccessClient>) {
+    use base64::Engine;
+    use base64::engine::general_purpose::URL_SAFE_NO_PAD;
+
+    let term_spec = &[(1, (0, 3))];
+    let file = client.upload_random_file(term_spec, 2048).await.unwrap();
+
+    let response = client.get_reconstruction_v2(&file.file_hash, None).await.unwrap().unwrap();
+
+    for fetch_entries in response.xorbs.values() {
+        for fetch in fetch_entries {
+            assert!(!fetch.url.is_empty(), "URL should not be empty");
+
+            if fetch.url.starts_with("http://") || fetch.url.starts_with("https://") {
+                // Server-transformed URL: should point to fetch_term
+                assert!(fetch.url.contains("/fetch_term"), "HTTP URL should contain /fetch_term: {}", fetch.url);
+            } else {
+                // Direct client URL: should be valid base64
+                let decoded = URL_SAFE_NO_PAD.decode(&fetch.url);
+                assert!(decoded.is_ok(), "URL should be valid base64: {}", fetch.url);
+
+                let payload = String::from_utf8(decoded.unwrap()).unwrap();
+                let parts: Vec<&str> = payload.splitn(3, ':').collect();
+                assert_eq!(parts.len(), 3, "Payload should have 3 colon-separated parts");
+
+                let hash = xet_core_structures::merklehash::MerkleHash::from_hex(parts[0]);
+                assert!(hash.is_ok(), "Hash part should be valid hex");
+
+                let ts: std::result::Result<u64, _> = parts[1].parse();
+                assert!(ts.is_ok(), "Timestamp should be a valid u64");
+
+                for range_str in parts[2].split(',').filter(|s| !s.is_empty()) {
+                    let range_parts: Vec<&str> = range_str.split('-').collect();
+                    assert_eq!(range_parts.len(), 2, "Each range should be start-end");
+                    assert!(range_parts[0].parse::<u64>().is_ok());
+                    assert!(range_parts[1].parse::<u64>().is_ok());
+                }
+            }
+        }
+    }
+}

xet_client/src/cas_client/simulation/direct_access_client.rs

@@ -14,7 +14,9 @@ use xet_core_structures::xorb_object::XorbObject;
 
 use super::super::error::Result;
 use super::super::interface::Client;
-use crate::cas_types::{FileRange, XorbReconstructionFetchInfo};
+use crate::cas_types::{
+    FileRange, QueryReconstructionResponse, QueryReconstructionResponseV2, XorbReconstructionFetchInfo,
+};
 
 /// A Client with direct access to XORB and file storage.
 ///
@@ -40,6 +42,39 @@ pub trait DirectAccessClient: Client + Send + Sync {
     /// Pass `None` to disable the delay.
     fn set_api_delay_range(&self, delay_range: Option<Range<Duration>>);
 
+    /// Sets the maximum number of byte ranges per `XorbMultiRangeFetch` entry
+    /// in V2 reconstruction responses.
+    ///
+    /// Default is `usize::MAX` (all ranges in one fetch). When set to N,
+    /// ranges for each xorb are grouped into entries of at most N ranges.
+    /// This simulates the CloudFront URL length limit that forces splitting.
+    fn set_max_ranges_per_fetch(&self, max_ranges: usize);
+
+    /// Disables V2 reconstruction responses with the given HTTP status code.
+    /// When disabled, the V2 endpoint returns this status, forcing clients to
+    /// fall back to V1. Pass 0 to re-enable.
+    fn disable_v2_reconstruction(&self, status_code: u16);
+
+    /// Returns the HTTP status code the V2 endpoint should return when disabled,
+    /// or 0 if V2 is enabled.
+    fn v2_disabled_status_code(&self) -> u16 {
+        0
+    }
+
+    /// V1 reconstruction: returns per-range presigned URLs.
+    async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponse>>;
+
+    /// V2 reconstruction: returns per-xorb multi-range fetch descriptors.
+    async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>>;
+
     /// Applies the configured API delay if set.
     ///
     /// This method sleeps for a random duration within the configured delay range.

xet_client/src/cas_client/simulation/local_client.rs

@@ -5,14 +5,12 @@ use std::mem::size_of;
 use std::ops::Range;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicU16, AtomicU64, AtomicUsize, Ordering};
 
 use anyhow::anyhow;
 use async_trait::async_trait;
 use bytes::Bytes;
 use heed::types::*;
-use lazy_static::lazy_static;
-use more_asserts::*;
 use rand::Rng;
 use tempfile::TempDir;
 use tokio::time::{Duration, Instant};
@@ -30,25 +28,16 @@ use xet_core_structures::xorb_object::{SerializedXorbObject, XorbObject};
 use xet_runtime::file_utils::SafeFileCreator;
 
 use super::direct_access_client::DirectAccessClient;
+use super::xorb_utils::{self, REFERENCE_INSTANT};
 use crate::cas_client::Client;
 use crate::cas_client::adaptive_concurrency::AdaptiveConcurrencyController;
 use crate::cas_client::error::{CasClientError, Result};
 use crate::cas_client::progress_tracked_streams::ProgressCallback;
 use crate::cas_types::{
-    BatchQueryReconstructionResponse, ChunkRange, FileRange, HexMerkleHash, HttpRange, QueryReconstructionResponse,
-    XorbReconstructionFetchInfo, XorbReconstructionTerm,
+    BatchQueryReconstructionResponse, FileRange, HexMerkleHash, HttpRange, QueryReconstructionResponse,
+    QueryReconstructionResponseV2, XorbMultiRangeFetch, XorbRangeDescriptor, XorbReconstructionFetchInfo,
 };
 
-lazy_static! {
-    /// Reference instant for URL timestamps. Initialized far in the past to allow
-    /// testing timestamps that are earlier in the current process lifetime.
-    static ref REFERENCE_INSTANT: Instant = {
-        let now = Instant::now();
-        now.checked_sub(Duration::from_secs(365 * 24 * 60 * 60))
-            .unwrap_or(now)
-    };
-}
-
 pub struct LocalClient {
     // Note: Field order matters for Drop! heed::Env must be dropped before _tmp_dir
     // because heed holds file handles that need to be closed before the directory is deleted.
@@ -62,6 +51,10 @@ pub struct LocalClient {
     url_expiration_ms: AtomicU64,
     /// API delay range in milliseconds as (min_ms, max_ms). (0, 0) means disabled.
     random_ms_delay_window: (AtomicU64, AtomicU64),
+    /// Max ranges per XorbMultiRangeFetch entry. usize::MAX means no splitting.
+    max_ranges_per_fetch: AtomicUsize,
+    /// HTTP status code to return when V2 is disabled (0 = enabled).
+    v2_disabled_status: AtomicU16,
     _tmp_dir: Option<TempDir>, // Must be last - dropped after heed env is closed
 }
 
@@ -157,6 +150,8 @@ impl LocalClient {
             upload_concurrency_controller: AdaptiveConcurrencyController::new_upload("local_uploads"),
             url_expiration_ms: AtomicU64::new(u64::MAX),
             random_ms_delay_window: (AtomicU64::new(0), AtomicU64::new(0)),
+            max_ranges_per_fetch: AtomicUsize::new(usize::MAX),
+            v2_disabled_status: AtomicU16::new(0),
             _tmp_dir: tmp_dir, // Must be last - dropped after heed env is closed
         })
     }
@@ -347,6 +342,34 @@ impl DirectAccessClient for LocalClient {
         self.url_expiration_ms.store(expiration.as_millis() as u64, Ordering::Relaxed);
     }
 
+    fn set_max_ranges_per_fetch(&self, max_ranges: usize) {
+        self.max_ranges_per_fetch.store(max_ranges, Ordering::Relaxed);
+    }
+
+    fn disable_v2_reconstruction(&self, status_code: u16) {
+        self.v2_disabled_status.store(status_code, Ordering::Relaxed);
+    }
+
+    fn v2_disabled_status_code(&self) -> u16 {
+        self.v2_disabled_status.load(Ordering::Relaxed)
+    }
+
+    async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponse>> {
+        LocalClient::get_reconstruction_v1(self, file_id, bytes_range).await
+    }
+
+    async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        LocalClient::get_reconstruction_v2(self, file_id, bytes_range).await
+    }
+
     fn set_api_delay_range(&self, delay_range: Option<Range<Duration>>) {
         match delay_range {
             Some(range) => {
@@ -626,7 +649,126 @@ impl DirectAccessClient for LocalClient {
     }
 }
 
-/// LocalClient is responsible for writing/reading Xorbs on the local disk.
+impl LocalClient {
+    async fn compute_reconstruction_ranges(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<xorb_utils::ReconstructionRangesResult> {
+        let Some((file_info, _)) = self.shard_manager.get_file_reconstruction_info(file_id).await? else {
+            return Ok(None);
+        };
+
+        xorb_utils::compute_reconstruction_ranges(&file_info, bytes_range, &mut |hash| self.xorb_footer_sync(hash))
+    }
+
+    fn xorb_footer_sync(&self, hash: &MerkleHash) -> Result<XorbObject> {
+        let file_path = self.get_path_for_entry(hash);
+        let mut file = File::open(&file_path).map_err(|_| {
+            error!("Unable to find file in local CAS {:?}", file_path);
+            CasClientError::XORBNotFound(*hash)
+        })?;
+        XorbObject::deserialize(&mut file).map_err(Into::into)
+    }
+
+    /// V1 reconstruction: returns per-range presigned URLs.
+    pub async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponse>> {
+        self.apply_api_delay().await;
+
+        let result = self.compute_reconstruction_ranges(file_id, bytes_range).await?;
+        let Some((offset_into_first_range, terms, merged_ranges)) = result else {
+            return Ok(None);
+        };
+
+        if terms.is_empty() {
+            return Ok(Some(QueryReconstructionResponse {
+                offset_into_first_range,
+                terms,
+                fetch_info: HashMap::new(),
+            }));
+        }
+
+        let timestamp = Instant::now();
+        let mut fetch_info: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>> = HashMap::new();
+        for (hash, ranges) in merged_ranges {
+            let file_path = self.get_path_for_entry(&hash);
+            let entries = ranges
+                .into_iter()
+                .map(|r| XorbReconstructionFetchInfo {
+                    range: r.chunk_range,
+                    url: generate_fetch_url(&file_path, &r.byte_range, timestamp),
+                    url_range: HttpRange::from(r.byte_range),
+                })
+                .collect();
+            fetch_info.insert(hash.into(), entries);
+        }
+
+        Ok(Some(QueryReconstructionResponse {
+            offset_into_first_range,
+            terms,
+            fetch_info,
+        }))
+    }
+
+    /// V2 reconstruction: returns per-xorb multi-range fetch descriptors.
+    pub async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        self.apply_api_delay().await;
+
+        let result = self.compute_reconstruction_ranges(file_id, bytes_range).await?;
+        let Some((offset_into_first_range, terms, merged_ranges)) = result else {
+            return Ok(None);
+        };
+
+        if terms.is_empty() {
+            return Ok(Some(QueryReconstructionResponseV2 {
+                offset_into_first_range,
+                terms,
+                xorbs: HashMap::new(),
+            }));
+        }
+
+        let timestamp = Instant::now();
+        let max_ranges = self.max_ranges_per_fetch.load(Ordering::Relaxed);
+
+        let mut xorbs: HashMap<HexMerkleHash, Vec<XorbMultiRangeFetch>> = HashMap::new();
+        for (hash, ranges) in merged_ranges {
+            let mut fetch_entries = Vec::new();
+
+            for chunk in ranges.chunks(max_ranges) {
+                let range_descriptors: Vec<XorbRangeDescriptor> = chunk
+                    .iter()
+                    .map(|r| XorbRangeDescriptor {
+                        chunks: r.chunk_range,
+                        bytes: HttpRange::from(r.byte_range),
+                    })
+                    .collect();
+
+                let url = generate_v2_fetch_url(&hash, &range_descriptors, timestamp);
+                fetch_entries.push(XorbMultiRangeFetch {
+                    url,
+                    ranges: range_descriptors,
+                });
+            }
+
+            xorbs.insert(hash.into(), fetch_entries);
+        }
+
+        Ok(Some(QueryReconstructionResponseV2 {
+            offset_into_first_range,
+            terms,
+            xorbs,
+        }))
+    }
+}
+
 #[async_trait]
 impl Client for LocalClient {
     async fn get_file_reconstruction_info(
@@ -784,196 +926,8 @@ impl Client for LocalClient {
         &self,
         file_id: &MerkleHash,
         bytes_range: Option<FileRange>,
-    ) -> Result<Option<QueryReconstructionResponse>> {
-        self.apply_api_delay().await;
-        let Some((file_info, _)) = self.shard_manager.get_file_reconstruction_info(file_id).await? else {
-            return Ok(None);
-        };
-
-        // Calculate total file size from segments
-        let total_file_size: u64 = file_info.file_size();
-        // Handle range validation and truncation
-        let file_range = if let Some(range) = bytes_range {
-            // If the entire range is out of bounds, return None (like RemoteClient does for 416)
-            if range.start >= total_file_size {
-                // For empty files (size 0), only the first query (start == 0) should return the empty reconstruction
-                // All subsequent queries should return None to prevent infinite remainder loops
-                if total_file_size == 0 && range.start == 0 {
-                    // Empty file - return valid but empty reconstruction
-                    return Ok(Some(QueryReconstructionResponse {
-                        offset_into_first_range: 0,
-                        terms: vec![],
-                        fetch_info: HashMap::new(),
-                    }));
-                }
-                return Ok(None);
-            }
-            // Truncate end if it extends beyond file size
-            FileRange::new(range.start, range.end.min(total_file_size))
-        } else {
-            // No range specified - handle empty files
-            if total_file_size == 0 {
-                return Ok(Some(QueryReconstructionResponse {
-                    offset_into_first_range: 0,
-                    terms: vec![],
-                    fetch_info: HashMap::new(),
-                }));
-            }
-            FileRange::full()
-        };
-
-        // First skip file segments until we find the first one that starts before the file range start
-        let mut s_idx = 0;
-        let mut cumulative_bytes = 0u64;
-        let mut first_chunk_byte_start;
-
-        loop {
-            if s_idx >= file_info.segments.len() {
-                // We have here that the requested file range is out of bounds,
-                // so return a range error.
-                return Err(CasClientError::InvalidRange);
-            }
-
-            let n = file_info.segments[s_idx].unpacked_segment_bytes as u64;
-            if cumulative_bytes + n > file_range.start {
-                assert_ge!(file_range.start, cumulative_bytes);
-                first_chunk_byte_start = cumulative_bytes;
-                break;
-            } else {
-                cumulative_bytes += n;
-                s_idx += 1;
-            }
-        }
-
-        // Now, prepare the response by iterating over the segments and
-        // adding the terms and fetch info to the response.
-        let mut terms = Vec::new();
-
-        #[derive(Clone)]
-        struct FetchInfoIntermediate {
-            chunk_range: ChunkRange,
-            byte_range: FileRange,
-        }
-
-        let mut fetch_info_map: HashMap<MerkleHash, Vec<FetchInfoIntermediate>> = HashMap::new();
-
-        while s_idx < file_info.segments.len() && cumulative_bytes < file_range.end {
-            let mut segment = file_info.segments[s_idx].clone();
-            let mut chunk_range = ChunkRange::new(segment.chunk_index_start, segment.chunk_index_end);
-
-            // Now get the URL for this segment, which involves reading the actual byte range there.
-            let xorb_footer = self.xorb_footer(&segment.xorb_hash).await?;
-
-            // Do we need to prune the first segment on chunk boundaries to align with the range given?
-            if cumulative_bytes < file_range.start {
-                while chunk_range.start < chunk_range.end {
-                    let next_chunk_size = xorb_footer.uncompressed_chunk_length(chunk_range.start)? as u64;
-
-                    if cumulative_bytes + next_chunk_size <= file_range.start {
-                        cumulative_bytes += next_chunk_size;
-                        first_chunk_byte_start += next_chunk_size;
-                        segment.unpacked_segment_bytes -= next_chunk_size as u32;
-
-                        chunk_range.start += 1;
-
-                        // Should find it somewhere in here.
-                        debug_assert_lt!(chunk_range.start, chunk_range.end);
-                    } else {
-                        break;
-                    }
-                }
-            }
-
-            // Do we need to prune the last segment on chunk boundaries to align with the range given?
-            if cumulative_bytes + segment.unpacked_segment_bytes as u64 > file_range.end {
-                while chunk_range.end > chunk_range.start {
-                    let last_chunk_size = xorb_footer.uncompressed_chunk_length(chunk_range.end - 1)?;
-
-                    if cumulative_bytes + (segment.unpacked_segment_bytes - last_chunk_size) as u64 >= file_range.end {
-                        // We can cut the last chunk off and still contain the requested range.
-                        chunk_range.end -= 1;
-                        segment.unpacked_segment_bytes -= last_chunk_size;
-                        debug_assert_lt!(chunk_range.start, chunk_range.end);
-                        debug_assert_gt!(segment.unpacked_segment_bytes, 0);
-                    } else {
-                        break;
-                    }
-                }
-            }
-
-            let (byte_start, byte_end) = xorb_footer.get_byte_offset(chunk_range.start, chunk_range.end)?;
-            let byte_range = FileRange::new(byte_start as u64, byte_end as u64);
-
-            let xorb_reconstruction_term = XorbReconstructionTerm {
-                hash: segment.xorb_hash.into(),
-                unpacked_length: segment.unpacked_segment_bytes,
-                range: chunk_range,
-            };
-
-            terms.push(xorb_reconstruction_term);
-
-            let fetch_info_intemediate = FetchInfoIntermediate {
-                chunk_range,
-                byte_range,
-            };
-
-            fetch_info_map
-                .entry(segment.xorb_hash)
-                .or_default()
-                .push(fetch_info_intemediate);
-
-            cumulative_bytes += segment.unpacked_segment_bytes as u64;
-            s_idx += 1;
-        }
-
-        assert!(!terms.is_empty());
-
-        let timestamp = Instant::now();
-
-        // Sort and merge adjacent/overlapping ranges in each fetch_info Vec
-        let mut merged_fetch_info_map: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>> = HashMap::new();
-        for (hash, mut fi_vec) in fetch_info_map {
-            // Sort by url_range.start
-            fi_vec.sort_by_key(|fi| fi.chunk_range.start);
-            let file_path = self.get_path_for_entry(&hash);
-
-            // Merge adjacent or overlapping ranges
-            let mut merged: Vec<XorbReconstructionFetchInfo> = Vec::new();
-            let mut idx = 0;
-
-            while idx < fi_vec.len() {
-                // Go through and merge adjascent or overlapping ranges,
-                // then form the full XorbReconstructionFetchInfo structs.
-                let mut new_fi = fi_vec[idx].clone();
-
-                while idx + 1 < fi_vec.len() {
-                    let next_fi = &fi_vec[idx + 1];
-                    if next_fi.chunk_range.start <= new_fi.chunk_range.end {
-                        new_fi.chunk_range.end = next_fi.chunk_range.end.max(new_fi.chunk_range.end);
-                        new_fi.byte_range.end = next_fi.byte_range.end.max(new_fi.byte_range.end);
-                        idx += 1;
-                    } else {
-                        break;
-                    }
-                }
-
-                merged.push(XorbReconstructionFetchInfo {
-                    range: new_fi.chunk_range,
-                    url: generate_fetch_url(&file_path, &new_fi.byte_range, timestamp),
-                    url_range: HttpRange::from(new_fi.byte_range),
-                });
-
-                idx += 1;
-            }
-
-            merged_fetch_info_map.insert(hash.into(), merged);
-        }
-
-        Ok(Some(QueryReconstructionResponse {
-            offset_into_first_range: file_range.start - first_chunk_byte_start,
-            terms,
-            fetch_info: merged_fetch_info_map,
-        }))
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        self.get_reconstruction_v2(file_id, bytes_range).await
     }
 
     async fn batch_get_reconstruction(&self, file_ids: &[MerkleHash]) -> Result<BatchQueryReconstructionResponse> {
@@ -982,7 +936,7 @@ impl Client for LocalClient {
         let mut fetch_info_map: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>> = HashMap::new();
 
         for file_id in file_ids {
-            if let Some(response) = self.get_reconstruction(file_id, None).await? {
+            if let Some(response) = self.get_reconstruction_v1(file_id, None).await? {
                 let hex_hash: HexMerkleHash = (*file_id).into();
                 files.insert(hex_hash, response.terms);
 
@@ -1013,8 +967,14 @@ impl Client for LocalClient {
         // Retry loop: try to fetch, and if URL expired, refresh and retry once.
         for attempt in 0..2 {
             self.apply_api_delay().await;
-            let (url, range) = url_info.retrieve_url().await?;
-            let (file_path, _url_byte_range, url_timestamp) = parse_fetch_url(&url)?;
+            let (url, http_ranges) = url_info.retrieve_url().await?;
+
+            let (file_path, url_timestamp) = if let Ok((path, _, ts)) = parse_fetch_url(&url) {
+                (path, ts)
+            } else {
+                let (hash, ts, _) = xorb_utils::parse_v2_fetch_url(&url)?;
+                (self.get_path_for_entry(&hash), ts)
+            };
 
             // Check if URL has expired
             let expiration_ms = self.url_expiration_ms.load(Ordering::Relaxed);
@@ -1028,34 +988,46 @@ impl Client for LocalClient {
                 return Err(CasClientError::PresignedUrlExpirationError);
             }
 
-            // Read the byte range from the file and deserialize
+            // Read each byte range from the serialized file and deserialize the chunks.
             let mut file = File::open(&file_path).map_err(|_| CasClientError::XORBNotFound(MerkleHash::default()))?;
-            let start = range.start;
-            let end = range.end + 1; // HttpRange is inclusive end
-            file.seek(SeekFrom::Start(start))?;
-            let len = (end - start) as usize;
+
+            let mut all_decompressed = Vec::new();
+            let mut all_chunk_indices = Vec::<u32>::new();
+            let mut total_transfer = 0u64;
+
+            for http_range in &http_ranges {
+                let len = http_range.length() as usize;
+                total_transfer += http_range.length();
+
+                file.seek(SeekFrom::Start(http_range.start))?;
                 let mut data = vec![0u8; len];
                 std::io::Read::read_exact(&mut file, &mut data)?;
 
-            // Deserialize the chunks from the raw XORB data
-            let (decompressed_data, chunk_byte_indices) =
+                let (decompressed, chunk_indices) =
                     xet_core_structures::xorb_object::deserialize_chunks(&mut Cursor::new(&data))?;
 
-            if let Some(expected) = uncompressed_size_if_known {
-                debug_assert_eq!(
-                    decompressed_data.len(),
-                    expected,
-                    "get_file_term_data: expected {} bytes, got {}",
-                    expected,
-                    decompressed_data.len()
+                xet_core_structures::xorb_object::append_chunk_segment(
+                    &mut all_decompressed,
+                    &mut all_chunk_indices,
+                    &decompressed,
+                    &chunk_indices,
                 );
             }
 
-            let transfer_len = len as u64;
-            if let Some(ref cb) = progress_callback {
-                cb(transfer_len, transfer_len, transfer_len);
+            if let Some(expected) = uncompressed_size_if_known {
+                debug_assert_eq!(
+                    all_decompressed.len(),
+                    expected,
+                    "get_file_term_data: expected {} bytes, got {}",
+                    expected,
+                    all_decompressed.len()
+                );
             }
-            return Ok((Bytes::from(decompressed_data), chunk_byte_indices));
+
+            if let Some(ref cb) = progress_callback {
+                cb(total_transfer, total_transfer, total_transfer);
+            }
+            return Ok((Bytes::from(all_decompressed), all_chunk_indices));
         }
 
         // Should not reach here, but return error if we do.
@@ -1093,6 +1065,10 @@ fn parse_fetch_url(url: &str) -> Result<(PathBuf, FileRange, Instant)> {
 
     Ok((file_path, byte_range, timestamp))
 }
+
+fn generate_v2_fetch_url(hash: &MerkleHash, ranges: &[XorbRangeDescriptor], timestamp: Instant) -> String {
+    xorb_utils::generate_v2_fetch_url(hash, ranges, timestamp)
+}
 #[cfg(test)]
 mod tests {
     use xet_core_structures::xorb_object::xorb_format_test_utils::{
@@ -1102,7 +1078,7 @@ mod tests {
     use super::*;
     use crate::cas_client::simulation::DeletionControlableClient;
     use crate::cas_client::simulation::client_testing_utils::ClientTestingUtils;
-    use crate::cas_types::XorbReconstructionFetchInfo;
+    use crate::cas_types::{ChunkRange, XorbReconstructionFetchInfo};
 
     /// Runs the common TestingClient trait test suite for LocalClient.
     #[tokio::test]

xet_client/src/cas_client/simulation/local_server/handlers.rs

@@ -32,8 +32,8 @@ use super::super::super::error::CasClientError;
 use super::super::super::{DeletionControlableClient, DirectAccessClient};
 use super::latency_simulation::{LatencySimulation, ServerLatencyProfile};
 use crate::cas_types::{
-    FileRange, HexKey, HexMerkleHash, UploadShardResponse, UploadShardResponseType, UploadXorbResponse,
-    XorbReconstructionFetchInfo,
+    FileRange, HexKey, HexMerkleHash, QueryReconstructionResponseV2, UploadShardResponse, UploadShardResponseType,
+    UploadXorbResponse, XorbRangeDescriptor, XorbReconstructionFetchInfo,
 };
 
 /// Server state passed to all handlers.
@@ -128,27 +128,55 @@ pub(super) fn error_to_response(e: CasClientError) -> Response {
     (status, e.to_string()).into_response()
 }
 
-/// Encodes term data (file path) into a URL-safe base64 string.
-///
-/// The term encodes the local file path that the LocalClient uses.
-/// This allows the fetch_term endpoint to retrieve the data.
-/// Encodes a fetch term for HTTP transport.
-///
-/// The encoded term contains:
-/// - xorb_hash: The XORB hash (hex encoded)
-///
-/// The byte range to fetch comes from the HTTP Range header, not encoded in the term.
+/// Encodes a V1 fetch term for HTTP transport.
+/// Contains only the xorb hash; the byte range comes from the HTTP Range header.
 fn encode_term(xorb_hash: &MerkleHash) -> String {
     URL_SAFE_NO_PAD.encode(xorb_hash.hex().as_bytes())
 }
 
-/// Decodes a fetch term back into its components.
-///
-/// Returns the xorb_hash.
-fn decode_term(term: &str) -> Result<MerkleHash, String> {
+/// Encodes a V2 fetch term with embedded byte ranges.
+/// Format: "{hash_hex}:{start1}-{end1},{start2}-{end2},..."
+/// Byte ranges use exclusive end (FileRange convention).
+fn encode_term_with_ranges(xorb_hash: &MerkleHash, ranges: &[XorbRangeDescriptor]) -> String {
+    let ranges_str: Vec<String> = ranges
+        .iter()
+        .map(|r| {
+            let file_range = FileRange::from(r.bytes);
+            format!("{}-{}", file_range.start, file_range.end)
+        })
+        .collect();
+    let payload = format!("{}:{}", xorb_hash.hex(), ranges_str.join(","));
+    URL_SAFE_NO_PAD.encode(payload.as_bytes())
+}
+
+/// Decoded fetch term: hash and optional byte ranges (exclusive end).
+struct DecodedTerm {
+    hash: MerkleHash,
+    byte_ranges: Vec<FileRange>,
+}
+
+/// Decodes a fetch term. Supports both V1 (hash only) and V2 (hash + ranges).
+fn decode_term(term: &str) -> Result<DecodedTerm, String> {
     let bytes = URL_SAFE_NO_PAD.decode(term).map_err(|e| format!("Invalid base64: {e}"))?;
-    let hash_hex = String::from_utf8(bytes).map_err(|e| format!("Invalid UTF-8: {e}"))?;
-    MerkleHash::from_hex(&hash_hex).map_err(|e| format!("Invalid hash: {e}"))
+    let payload = String::from_utf8(bytes).map_err(|e| format!("Invalid UTF-8: {e}"))?;
+
+    if let Some((hash_hex, ranges_str)) = payload.split_once(':') {
+        let hash = MerkleHash::from_hex(hash_hex).map_err(|e| format!("Invalid hash: {e}"))?;
+        let mut byte_ranges = Vec::new();
+        for r in ranges_str.split(',').filter(|s| !s.is_empty()) {
+            let (start_s, end_s) = r.split_once('-').ok_or("Invalid range syntax")?;
+            let start: u64 = start_s.parse().map_err(|e| format!("Invalid range start: {e}"))?;
+            let end: u64 = end_s.parse().map_err(|e| format!("Invalid range end: {e}"))?;
+            byte_ranges.push(FileRange::new(start, end));
+        }
+        Ok(DecodedTerm { hash, byte_ranges })
+    } else {
+        let hash = MerkleHash::from_hex(&payload).map_err(|e| format!("Invalid hash: {e}"))?;
+        Ok(DecodedTerm {
+            hash,
+            byte_ranges: vec![],
+        })
+    }
 }
 
 /// Extracts the base URL from request headers (Host header).
@@ -220,7 +248,7 @@ pub async fn get_reconstruction(
         Err((status, msg)) => return (status, msg).into_response(),
     };
 
-    match state.client.get_reconstruction(&file_id, range).await {
+    match state.client.get_reconstruction_v1(&file_id, range).await {
         Ok(Some(mut response)) => {
             transform_fetch_info_urls(&mut response.fetch_info, &base_url);
             Json(response).into_response()
@@ -230,6 +258,78 @@ pub async fn get_reconstruction(
     }
 }
 
+/// GET /v2/reconstructions/{file_id}
+///
+/// Returns V2 reconstruction information for a file, including:
+/// - List of terms (chunks) needed to reconstruct the file
+/// - Per-xorb fetch descriptors with multi-range URLs
+///
+/// Supports Range header for partial file reconstruction.
+/// URLs in the response point to the /v1/fetch_term endpoint.
+pub async fn get_reconstruction_v2(
+    State(state): State<ServerState>,
+    Path(HexMerkleHash(file_id)): Path<HexMerkleHash>,
+    headers: HeaderMap,
+) -> Response {
+    let connection_guard = state.latency_simulation.register_connection().await;
+    if let Some(simulated_error) = connection_guard.simulate_error() {
+        return simulated_error;
+    }
+
+    // Allow testing V1 fallback by simulating V2 endpoint unavailability.
+    let disabled_status = state.client.v2_disabled_status_code();
+    if disabled_status != 0 {
+        let code = StatusCode::from_u16(disabled_status).unwrap_or(StatusCode::NOT_FOUND);
+        return (code, "V2 reconstruction endpoint disabled").into_response();
+    }
+
+    let base_url = get_base_url(&headers);
+
+    let range = match parse_range_header(headers.get(RANGE)) {
+        Ok(Some(FileRangeVariant::Normal(range))) => Some(range),
+        Ok(Some(FileRangeVariant::OpenRHS(start))) => {
+            let file_size = match state.client.get_file_size(&file_id).await {
+                Ok(size) => size,
+                Err(e) => return error_to_response(e),
+            };
+            Some(FileRange::new(start, file_size))
+        },
+        Ok(Some(FileRangeVariant::Suffix(suffix))) => {
+            let file_size = match state.client.get_file_size(&file_id).await {
+                Ok(size) => size,
+                Err(e) => return error_to_response(e),
+            };
+            Some(FileRange::new(file_size.saturating_sub(suffix), file_size))
+        },
+        Ok(None) => None,
+        Err((status, msg)) => return (status, msg).into_response(),
+    };
+
+    match state.client.get_reconstruction_v2(&file_id, range).await {
+        Ok(Some(mut response)) => {
+            transform_v2_xorb_urls(&mut response, &base_url);
+            Json(response).into_response()
+        },
+        Ok(None) => (StatusCode::RANGE_NOT_SATISFIABLE, "Range not satisfiable").into_response(),
+        Err(e) => error_to_response(e),
+    }
+}
+
+/// Transforms V2 xorb URLs from client-internal format to HTTP URLs.
+///
+/// Each `XorbMultiRangeFetch` URL is replaced with an HTTP URL pointing
+/// to the /v1/fetch_term endpoint. The byte ranges from the V2 response
+/// are encoded into the term so the endpoint can serve all ranges in one request.
+fn transform_v2_xorb_urls(response: &mut QueryReconstructionResponseV2, base_url: &str) {
+    for (xorb_hash, fetch_entries) in response.xorbs.iter_mut() {
+        let xorb_hash: MerkleHash = (*xorb_hash).into();
+        for fetch in fetch_entries.iter_mut() {
+            let encoded_term = encode_term_with_ranges(&xorb_hash, &fetch.ranges);
+            fetch.url = format!("{base_url}/v1/fetch_term?term={encoded_term}");
+        }
+    }
+}
+
 /// GET /reconstructions?file_id=...&file_id=...
 ///
 /// Batch query for reconstruction information for multiple files using query parameters.
@@ -285,10 +385,12 @@ pub async fn batch_get_reconstruction(
 /// GET /v1/fetch_term?term=<base64_encoded_term>
 ///
 /// Fetches raw XORB data based on an encoded term.
-/// The term contains the xorb hash. The byte range is specified via HTTP Range header.
 ///
-/// This endpoint is called by RemoteClient when fetching reconstruction terms.
-/// It returns raw (compressed) bytes that the client will decompress.
+/// For V1 terms (hash only), the byte range comes from the HTTP Range header.
+/// For V2 terms (hash + ranges), all encoded byte ranges are fetched and
+/// concatenated in order, allowing a single request to serve multi-range blocks.
+///
+/// Returns raw (compressed) bytes that the client will decompress.
 pub async fn fetch_term(State(state): State<ServerState>, uri: axum::http::Uri, headers: HeaderMap) -> Response {
     let connection_guard = state.latency_simulation.register_connection().await;
     if let Some(simulated_error) = connection_guard.simulate_error() {
@@ -304,13 +406,69 @@ pub async fn fetch_term(State(state): State<ServerState>, uri: axum::http::Uri,
         return (StatusCode::BAD_REQUEST, "Missing 'term' query parameter").into_response();
     };
 
-    let xorb_hash = match decode_term(&term) {
-        Ok(h) => h,
+    let decoded = match decode_term(&term) {
+        Ok(d) => d,
         Err(e) => return (StatusCode::BAD_REQUEST, format!("Invalid term: {e}")).into_response(),
     };
 
-    // Get total length of the raw XORB data for Range header handling
-    let total_length = match state.client.xorb_raw_length(&xorb_hash).await {
+    if !decoded.byte_ranges.is_empty() {
+        // If the client sends a single-range HTTP Range header, serve just that range.
+        // This simulates S3/CDN behavior where the Range header controls the response
+        // regardless of what ranges are encoded in the presigned URL. This is the
+        // common path when ranges are split into single-range requests based on
+        // the multirange thresholds (V2 URLs with individual requests).
+        if let Ok(Some(FileRangeVariant::Normal(range))) = parse_range_header(headers.get(RANGE)) {
+            return match state.client.get_xorb_raw_bytes(&decoded.hash, Some(range)).await {
+                Ok(data) => (StatusCode::PARTIAL_CONTENT, data).into_response(),
+                Err(e) => error_to_response(e),
+            };
+        }
+
+        if decoded.byte_ranges.len() == 1 {
+            let range = &decoded.byte_ranges[0];
+            return match state.client.get_xorb_raw_bytes(&decoded.hash, Some(*range)).await {
+                Ok(data) => (StatusCode::PARTIAL_CONTENT, data).into_response(),
+                Err(e) => error_to_response(e),
+            };
+        }
+
+        // Multiple ranges with no Range header override: return a multipart/byteranges
+        // response (RFC 7233 Section 4.1), matching S3/CloudFront multi-range format.
+        let total_length = match state.client.xorb_raw_length(&decoded.hash).await {
+            Ok(len) => len,
+            Err(e) => return error_to_response(e),
+        };
+
+        let boundary = "xet_multipart_boundary";
+        let mut response_body = Vec::new();
+
+        for range in &decoded.byte_ranges {
+            let data = match state.client.get_xorb_raw_bytes(&decoded.hash, Some(*range)).await {
+                Ok(d) => d,
+                Err(e) => return error_to_response(e),
+            };
+            // FileRange uses exclusive end; Content-Range header uses inclusive end.
+            let inclusive_end = range.end.saturating_sub(1);
+            let part_header = format!(
+                "--{boundary}\r\nContent-Type: application/octet-stream\r\nContent-Range: bytes {}-{}/{total_length}\r\n\r\n",
+                range.start, inclusive_end
+            );
+            response_body.extend_from_slice(part_header.as_bytes());
+            response_body.extend_from_slice(&data);
+            response_body.extend_from_slice(b"\r\n");
+        }
+        response_body.extend_from_slice(format!("--{boundary}--\r\n").as_bytes());
+
+        let content_type = format!("multipart/byteranges; boundary={boundary}");
+        let mut headers = HeaderMap::new();
+        headers.insert(http::header::CONTENT_TYPE, HeaderValue::from_str(&content_type).unwrap());
+
+        return (StatusCode::PARTIAL_CONTENT, headers, Bytes::from(response_body)).into_response();
+    }
+
+    // V1 term: byte range comes from the HTTP Range header.
+    // Get total length of the raw XORB data for Range header handling.
+    let total_length = match state.client.xorb_raw_length(&decoded.hash).await {
         Ok(len) => len,
         Err(e) => return error_to_response(e),
     };
@@ -327,7 +485,7 @@ pub async fn fetch_term(State(state): State<ServerState>, uri: axum::http::Uri,
     };
 
     // Fetch raw (serialized/compressed) bytes from the XORB
-    match state.client.get_xorb_raw_bytes(&xorb_hash, byte_range).await {
+    match state.client.get_xorb_raw_bytes(&decoded.hash, byte_range).await {
         Ok(data) => (StatusCode::OK, data).into_response(),
         Err(e) => error_to_response(e),
     }
@@ -713,9 +871,33 @@ mod tests {
         let xorb_hash = MerkleHash::from_hex(&format!("{:0>64}", "abc123")).unwrap();
 
         let encoded = encode_term(&xorb_hash);
-        let decoded_hash = decode_term(&encoded).unwrap();
+        let decoded = decode_term(&encoded).unwrap();
+        assert_eq!(decoded.hash, xorb_hash);
+        assert!(decoded.byte_ranges.is_empty());
+    }
 
-        assert_eq!(decoded_hash, xorb_hash);
+    #[test]
+    fn test_encode_decode_term_with_ranges() {
+        use crate::cas_types::{ChunkRange, HttpRange, XorbRangeDescriptor};
+
+        let xorb_hash = MerkleHash::from_hex(&format!("{:0>64}", "abc123")).unwrap();
+        let ranges = vec![
+            XorbRangeDescriptor {
+                chunks: ChunkRange::new(0, 3),
+                bytes: HttpRange::new(0, 1023),
+            },
+            XorbRangeDescriptor {
+                chunks: ChunkRange::new(5, 8),
+                bytes: HttpRange::new(2048, 4095),
+            },
+        ];
+
+        let encoded = encode_term_with_ranges(&xorb_hash, &ranges);
+        let decoded = decode_term(&encoded).unwrap();
+        assert_eq!(decoded.hash, xorb_hash);
+        assert_eq!(decoded.byte_ranges.len(), 2);
+        assert_eq!(decoded.byte_ranges[0], FileRange::new(0, 1024));
+        assert_eq!(decoded.byte_ranges[1], FileRange::new(2048, 4096));
     }
 
     #[test]

xet_client/src/cas_client/simulation/local_server/server.rs

@@ -177,6 +177,7 @@ impl LocalServer {
                     .route("/get_xorb/{prefix}/{hash}/", get(handlers::get_file_term_data))
                     .route("/fetch_term", get(handlers::fetch_term)),
             )
+            .nest("/v2", Router::new().route("/reconstructions/{file_id}", get(handlers::get_reconstruction_v2)))
             .nest(
                 "/simulation",
                 super::simulation_handlers::simulation_routes()
@@ -425,7 +426,7 @@ impl Client for LocalTestServer {
         &self,
         file_id: &xet_core_structures::merklehash::MerkleHash,
         bytes_range: Option<crate::cas_types::FileRange>,
-    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponseV2>> {
         self.remote_client.get_reconstruction(file_id, bytes_range).await
     }
 
@@ -492,6 +493,34 @@ impl DirectAccessClient for LocalTestServer {
         self.client.set_fetch_term_url_expiration(expiration);
     }
 
+    fn set_max_ranges_per_fetch(&self, max_ranges: usize) {
+        self.client.set_max_ranges_per_fetch(max_ranges);
+    }
+
+    fn disable_v2_reconstruction(&self, status_code: u16) {
+        self.client.disable_v2_reconstruction(status_code);
+    }
+
+    fn v2_disabled_status_code(&self) -> u16 {
+        self.client.v2_disabled_status_code()
+    }
+
+    async fn get_reconstruction_v1(
+        &self,
+        file_id: &xet_core_structures::merklehash::MerkleHash,
+        bytes_range: Option<crate::cas_types::FileRange>,
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+        self.remote_client.get_reconstruction_v1(file_id, bytes_range).await
+    }
+
+    async fn get_reconstruction_v2(
+        &self,
+        file_id: &xet_core_structures::merklehash::MerkleHash,
+        bytes_range: Option<crate::cas_types::FileRange>,
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponseV2>> {
+        self.remote_client.get_reconstruction_v2(file_id, bytes_range).await
+    }
+
     fn set_api_delay_range(&self, delay_range: Option<std::ops::Range<std::time::Duration>>) {
         self.client.set_api_delay_range(delay_range);
     }
@@ -588,7 +617,7 @@ mod tests {
     use crate::cas_client::simulation::client_testing_utils::ClientTestingUtils;
     use crate::cas_client::simulation::local_server::SimulationControlClient;
     use crate::cas_client::simulation::{DeletionControlableClient, DirectAccessClient};
-    use crate::cas_types::FileRange;
+    use crate::cas_types::{FileRange, QueryReconstructionResponseV2};
 
     const CHUNK_SIZE: usize = 123;
 
@@ -604,16 +633,16 @@ mod tests {
         let local_data = server.client().get_file_data(&file.file_hash, None).await.unwrap();
         assert_eq!(file.data, local_data);
 
-        // Full file reconstruction - compare remote and local
+        // Full file reconstruction - compare remote and local (V1)
         let remote_recon = server
             .remote_client()
-            .get_reconstruction(&file.file_hash, None)
+            .get_reconstruction_v1(&file.file_hash, None)
             .await
             .unwrap()
             .unwrap();
         let local_recon = server
             .client()
-            .get_reconstruction(&file.file_hash, None)
+            .get_reconstruction_v1(&file.file_hash, None)
             .await
             .unwrap()
             .unwrap();
@@ -629,7 +658,7 @@ mod tests {
         let range = FileRange::new(file_size / 4, file_size * 3 / 4);
         let range_recon = server
             .remote_client()
-            .get_reconstruction(&file.file_hash, Some(range))
+            .get_reconstruction_v1(&file.file_hash, Some(range))
             .await
             .unwrap();
         assert!(range_recon.is_some());
@@ -639,7 +668,7 @@ mod tests {
         let multi_file = server.client().upload_random_file(term_spec, CHUNK_SIZE).await.unwrap();
         let multi_recon = server
             .remote_client()
-            .get_reconstruction(&multi_file.file_hash, None)
+            .get_reconstruction_v1(&multi_file.file_hash, None)
             .await
             .unwrap()
             .unwrap();
@@ -750,7 +779,7 @@ mod tests {
         // Verify single XORB URLs are HTTP
         let recon1 = server
             .remote_client()
-            .get_reconstruction(&file1.file_hash, None)
+            .get_reconstruction_v1(&file1.file_hash, None)
             .await
             .unwrap()
             .unwrap();
@@ -770,7 +799,7 @@ mod tests {
         // Verify multi-XORB file has HTTP URLs for all XORBs
         let multi_recon = server
             .remote_client()
-            .get_reconstruction(&multi_file.file_hash, None)
+            .get_reconstruction_v1(&multi_file.file_hash, None)
             .await
             .unwrap()
             .unwrap();
@@ -786,7 +815,7 @@ mod tests {
         let range = FileRange::new(file_size / 4, file_size * 3 / 4);
         let range_recon = server
             .remote_client()
-            .get_reconstruction(&multi_file.file_hash, Some(range))
+            .get_reconstruction_v1(&multi_file.file_hash, Some(range))
             .await
             .unwrap()
             .unwrap();
@@ -817,7 +846,7 @@ mod tests {
         // Get reconstruction via remote client
         let recon = server
             .remote_client()
-            .get_reconstruction(&file.file_hash, None)
+            .get_reconstruction_v1(&file.file_hash, None)
             .await
             .unwrap()
             .unwrap();
@@ -841,7 +870,7 @@ mod tests {
         // Get reconstruction
         let recon = server
             .remote_client()
-            .get_reconstruction(&file.file_hash, None)
+            .get_reconstruction_v1(&file.file_hash, None)
             .await
             .unwrap()
             .unwrap();
@@ -906,6 +935,241 @@ mod tests {
         }
     }
 
+    /// Tests V2 reconstruction endpoint returns valid responses through the server.
+    async fn check_v2_reconstruction(server: &LocalTestServer) {
+        let file = server.client().upload_random_file(&[(1, (0, 5))], CHUNK_SIZE).await.unwrap();
+
+        // Query V2 endpoint via remote client
+        let v2 = server
+            .remote_client()
+            .get_reconstruction_v2(&file.file_hash, None)
+            .await
+            .unwrap()
+            .unwrap();
+
+        assert!(!v2.terms.is_empty());
+        assert!(!v2.xorbs.is_empty());
+        assert_eq!(v2.offset_into_first_range, 0);
+
+        // V2 URLs should be HTTP URLs pointing to /v1/fetch_term
+        for fetch_entries in v2.xorbs.values() {
+            for fetch in fetch_entries {
+                assert!(fetch.url.starts_with("http://"), "V2 URL should be HTTP, got: {}", fetch.url);
+                assert!(
+                    fetch.url.contains("/v1/fetch_term?term="),
+                    "V2 URL should point to fetch_term endpoint, got: {}",
+                    fetch.url
+                );
+            }
+        }
+
+        // V2 terms should match V1 terms
+        let v1 = server
+            .remote_client()
+            .get_reconstruction_v1(&file.file_hash, None)
+            .await
+            .unwrap()
+            .unwrap();
+
+        assert_eq!(v1.terms.len(), v2.terms.len());
+        assert_eq!(v1.offset_into_first_range, v2.offset_into_first_range);
+        for (t1, t2) in v1.terms.iter().zip(v2.terms.iter()) {
+            assert_eq!(t1.hash, t2.hash);
+            assert_eq!(t1.range, t2.range);
+        }
+    }
+
+    /// Tests V2 fetch URLs are fetchable via the /v1/fetch_term endpoint.
+    async fn check_v2_url_transformation(server: &LocalTestServer) {
+        let http_client = reqwest::Client::new();
+
+        let file = server
+            .client()
+            .upload_random_file(&[(1, (0, 3)), (2, (0, 2))], CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        let v2 = server
+            .remote_client()
+            .get_reconstruction_v2(&file.file_hash, None)
+            .await
+            .unwrap()
+            .unwrap();
+
+        for fetch_entries in v2.xorbs.values() {
+            for fetch in fetch_entries {
+                let response = http_client.get(&fetch.url).send().await.unwrap();
+                assert!(
+                    response.status().is_success(),
+                    "V2 fetch URL should be fetchable: {} (status: {})",
+                    fetch.url,
+                    response.status()
+                );
+                let data = response.bytes().await.unwrap();
+                assert!(!data.is_empty(), "Fetched data should not be empty");
+            }
+        }
+    }
+
+    /// Tests V2 with range requests through the server.
+    async fn check_v2_range_reconstruction(server: &LocalTestServer) {
+        let term_spec = &[(1, (0, 3)), (2, (0, 2)), (1, (3, 5))];
+        let file = server.client().upload_random_file(term_spec, CHUNK_SIZE).await.unwrap();
+        let file_size = file.data.len() as u64;
+
+        let range = FileRange::new(file_size / 4, file_size * 3 / 4);
+        let v2 = server
+            .remote_client()
+            .get_reconstruction_v2(&file.file_hash, Some(range))
+            .await
+            .unwrap()
+            .unwrap();
+
+        assert!(!v2.terms.is_empty());
+        for fetch_entries in v2.xorbs.values() {
+            for fetch in fetch_entries {
+                assert!(fetch.url.starts_with("http://"));
+            }
+        }
+
+        // Validate open-ended and suffix range variants through the V2 HTTP endpoint.
+        let v2_url = format!("{}/v2/reconstructions/{}", server.endpoint(), file.file_hash.hex());
+        let http_client = reqwest::Client::new();
+
+        let open_rhs: QueryReconstructionResponseV2 = http_client
+            .get(&v2_url)
+            .header(reqwest::header::RANGE, "bytes=100-")
+            .send()
+            .await
+            .unwrap()
+            .error_for_status()
+            .unwrap()
+            .json()
+            .await
+            .unwrap();
+        assert!(!open_rhs.terms.is_empty());
+
+        let suffix: QueryReconstructionResponseV2 = http_client
+            .get(&v2_url)
+            .header(reqwest::header::RANGE, "bytes=-128")
+            .send()
+            .await
+            .unwrap()
+            .error_for_status()
+            .unwrap()
+            .json()
+            .await
+            .unwrap();
+        assert!(!suffix.terms.is_empty());
+    }
+
+    /// Tests V2 max_ranges_per_fetch through the server.
+    async fn check_v2_max_ranges(server: &LocalTestServer) {
+        let term_spec = &[(1, (0, 2)), (2, (0, 1)), (1, (2, 4)), (2, (1, 2)), (1, (4, 6))];
+        let file = server.client().upload_random_file(term_spec, 512).await.unwrap();
+
+        // Set max_ranges_per_fetch to 1
+        server.set_max_ranges_per_fetch(1);
+
+        let v2 = server
+            .client()
+            .get_reconstruction_v2(&file.file_hash, None)
+            .await
+            .unwrap()
+            .unwrap();
+
+        let xorb1_hash: crate::cas_types::HexMerkleHash = file.terms[0].xorb_hash.into();
+        if let Some(desc) = v2.xorbs.get(&xorb1_hash) {
+            for fetch in desc {
+                assert!(fetch.ranges.len() <= 1, "Each fetch should have at most 1 range, got {}", fetch.ranges.len());
+            }
+        }
+
+        // Reset
+        server.set_max_ranges_per_fetch(usize::MAX);
+    }
+
+    /// Verifies that disabling V2 with various status codes causes the V2 endpoint
+    /// to return that code, and that get_reconstruction falls back to V1.
+    async fn check_v2_disabled_fallback(server: &LocalTestServer) {
+        let file = server
+            .remote_client()
+            .upload_random_file(&[(1, (0, 3)), (2, (0, 2))], CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        // V2 should work before disabling.
+        let v2_result = server.remote_client().get_reconstruction_v2(&file.file_hash, None).await;
+        assert!(v2_result.is_ok());
+
+        // Test 501 (Not Implemented) fallback first, before the RemoteClient
+        // caches a V1 preference from a 404 fallback.
+        server.disable_v2_reconstruction(501);
+
+        let v2_result = server.remote_client().get_reconstruction_v2(&file.file_hash, None).await;
+        assert!(v2_result.is_err(), "V2 should return error when disabled with 501");
+
+        // Forced V2 should surface the endpoint error directly with no fallback.
+        let forced_v2 = server
+            .remote_client()
+            .get_reconstruction_with_version_override(&file.file_hash, None, Some(2))
+            .await;
+        assert!(forced_v2.is_err());
+        assert_eq!(forced_v2.unwrap_err().status(), Some(reqwest::StatusCode::NOT_IMPLEMENTED));
+
+        // Forced V1 should continue to succeed when V2 is disabled.
+        let forced_v1 = server
+            .remote_client()
+            .get_reconstruction_with_version_override(&file.file_hash, None, Some(1))
+            .await
+            .unwrap()
+            .unwrap();
+        assert_eq!(forced_v1.terms.len(), 2);
+
+        let result = server
+            .remote_client()
+            .get_reconstruction(&file.file_hash, None)
+            .await
+            .unwrap()
+            .unwrap();
+        assert_eq!(result.terms.len(), 2);
+
+        // Re-enable V2, then test 404 fallback.
+        server.disable_v2_reconstruction(0);
+
+        // Reset the RemoteClient's cached version by making a successful V2 call.
+        let v2_result = server.remote_client().get_reconstruction_v2(&file.file_hash, None).await;
+        assert!(v2_result.is_ok(), "V2 should work again after re-enabling");
+
+        server.disable_v2_reconstruction(404);
+
+        let v2_result = server.remote_client().get_reconstruction_v2(&file.file_hash, None).await;
+        assert!(v2_result.is_err(), "V2 should return error when disabled with 404");
+
+        let forced_v2 = server
+            .remote_client()
+            .get_reconstruction_with_version_override(&file.file_hash, None, Some(2))
+            .await;
+        assert!(forced_v2.is_err());
+        assert_eq!(forced_v2.unwrap_err().status(), Some(reqwest::StatusCode::NOT_FOUND));
+
+        let forced_v1 = server
+            .remote_client()
+            .get_reconstruction_with_version_override(&file.file_hash, None, Some(1))
+            .await
+            .unwrap()
+            .unwrap();
+        assert_eq!(forced_v1.terms.len(), 2);
+
+        let result = server
+            .remote_client()
+            .get_reconstruction(&file.file_hash, None)
+            .await
+            .unwrap()
+            .unwrap();
+        assert_eq!(result.terms.len(), 2);
+    }
+
     /// Runs all server checks for a given test server instance.
     async fn run_all_server_checks(server: &LocalTestServer) {
         check_basic_correctness(server).await;
@@ -915,6 +1179,11 @@ mod tests {
         check_downloaded_terms_match_expected_data(server).await;
         check_complete_file_reconstruction(server).await;
         check_chunk_hashes_correctness(server).await;
+        check_v2_reconstruction(server).await;
+        check_v2_url_transformation(server).await;
+        check_v2_range_reconstruction(server).await;
+        check_v2_max_ranges(server).await;
+        check_v2_disabled_fallback(server).await;
     }
 
     async fn all_file_hashes(client: &LocalClient) -> HashSet<MerkleHash> {

xet_client/src/cas_client/simulation/local_server/simulation_control_client.rs

@@ -17,7 +17,7 @@ use crate::cas_client::RemoteClient;
 use crate::cas_client::error::{CasClientError, Result};
 use crate::cas_client::interface::Client;
 use crate::cas_client::simulation::{DeletionControlableClient, DirectAccessClient};
-use crate::cas_types::{FileRange, HexMerkleHash, XorbReconstructionFetchInfo};
+use crate::cas_types::{FileRange, HexMerkleHash, QueryReconstructionResponseV2, XorbReconstructionFetchInfo};
 
 /// A client that connects to a `LocalTestServer` via HTTP and provides access
 /// to both `DirectAccessClient` and `DeletionControlableClient` operations
@@ -91,7 +91,7 @@ impl Client for SimulationControlClient {
         &self,
         file_id: &MerkleHash,
         bytes_range: Option<FileRange>,
-    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
         self.remote_client.get_reconstruction(file_id, bytes_range).await
     }
 
@@ -172,6 +172,30 @@ impl DirectAccessClient for SimulationControlClient {
         // No-op: delays are applied server-side via set_api_delay_range
     }
 
+    fn set_max_ranges_per_fetch(&self, _max_ranges: usize) {
+        // No-op: SimulationControlClient configures server via HTTP; endpoint not yet implemented.
+    }
+
+    fn disable_v2_reconstruction(&self, _status_code: u16) {
+        // No-op: SimulationControlClient configures server via HTTP; endpoint not yet implemented.
+    }
+
+    async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+        self.remote_client.get_reconstruction_v1(file_id, bytes_range).await
+    }
+
+    async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        self.remote_client.get_reconstruction_v2(file_id, bytes_range).await
+    }
+
     /// Sets the API delay range via the `/simulation/config/api_delay` endpoint.
     fn set_api_delay_range(&self, delay_range: Option<Range<Duration>>) {
         let url = self.sim_url("/config/api_delay");

xet_client/src/cas_client/simulation/memory_client.rs

@@ -2,11 +2,10 @@ use std::collections::HashMap;
 use std::io::{BufReader, Cursor};
 use std::ops::Range;
 use std::sync::Arc;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicU16, AtomicU64, AtomicUsize, Ordering};
 
 use async_trait::async_trait;
 use bytes::Bytes;
-use more_asserts::{assert_ge, assert_gt, debug_assert_lt};
 use rand::Rng;
 use tokio::sync::RwLock;
 use tokio::time::{Duration, Instant};
@@ -26,21 +25,12 @@ use super::super::progress_tracked_streams::ProgressCallback;
 use super::client_testing_utils::{FileTermReference, RandomFileContents};
 use super::direct_access_client::DirectAccessClient;
 use super::random_xorb::RandomXorb;
+use super::xorb_utils::{self, REFERENCE_INSTANT};
 use crate::cas_types::{
-    BatchQueryReconstructionResponse, ChunkRange, FileRange, HexMerkleHash, HttpRange, QueryReconstructionResponse,
-    XorbReconstructionFetchInfo, XorbReconstructionTerm,
+    BatchQueryReconstructionResponse, FileRange, HexMerkleHash, HttpRange, QueryReconstructionResponse,
+    QueryReconstructionResponseV2, XorbMultiRangeFetch, XorbRangeDescriptor, XorbReconstructionFetchInfo,
 };
 
-lazy_static::lazy_static! {
-    /// Reference instant for URL timestamps. Initialized far in the past to allow
-    /// testing timestamps that are earlier in the current process lifetime.
-    static ref REFERENCE_INSTANT: Instant = {
-        let now = Instant::now();
-        now.checked_sub(Duration::from_secs(365 * 24 * 60 * 60))
-            .unwrap_or(now)
-    };
-}
-
 /// Stored XORB data: the serialized data and the deserialized XorbObject (header/footer).
 struct MaterializedXorb {
     serialized_data: Bytes,
@@ -69,6 +59,10 @@ pub struct MemoryClient {
     url_expiration_ms: AtomicU64,
     /// API delay range in milliseconds as (min_ms, max_ms). (0, 0) means disabled.
     random_ms_delay_window: (AtomicU64, AtomicU64),
+    /// Max ranges per XorbMultiRangeFetch entry. usize::MAX means no splitting.
+    max_ranges_per_fetch: AtomicUsize,
+    /// HTTP status code to return when V2 is disabled (0 = enabled).
+    v2_disabled_status: AtomicU16,
 }
 
 impl MemoryClient {
@@ -81,6 +75,8 @@ impl MemoryClient {
             upload_concurrency_controller: AdaptiveConcurrencyController::new_upload("memory_uploads"),
             url_expiration_ms: AtomicU64::new(u64::MAX),
             random_ms_delay_window: (AtomicU64::new(0), AtomicU64::new(0)),
+            max_ranges_per_fetch: AtomicUsize::new(usize::MAX),
+            v2_disabled_status: AtomicU16::new(0),
         })
     }
 
@@ -225,6 +221,8 @@ impl Default for MemoryClient {
             upload_concurrency_controller: AdaptiveConcurrencyController::new_upload("memory_uploads"),
             url_expiration_ms: AtomicU64::new(u64::MAX),
             random_ms_delay_window: (AtomicU64::new(0), AtomicU64::new(0)),
+            max_ranges_per_fetch: AtomicUsize::new(usize::MAX),
+            v2_disabled_status: AtomicU16::new(0),
         }
     }
 }
@@ -236,6 +234,34 @@ impl DirectAccessClient for MemoryClient {
         self.url_expiration_ms.store(expiration.as_millis() as u64, Ordering::Relaxed);
     }
 
+    fn set_max_ranges_per_fetch(&self, max_ranges: usize) {
+        self.max_ranges_per_fetch.store(max_ranges, Ordering::Relaxed);
+    }
+
+    fn disable_v2_reconstruction(&self, status_code: u16) {
+        self.v2_disabled_status.store(status_code, Ordering::Relaxed);
+    }
+
+    fn v2_disabled_status_code(&self) -> u16 {
+        self.v2_disabled_status.load(Ordering::Relaxed)
+    }
+
+    async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponse>> {
+        MemoryClient::get_reconstruction_v1(self, file_id, bytes_range).await
+    }
+
+    async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        MemoryClient::get_reconstruction_v2(self, file_id, bytes_range).await
+    }
+
     fn set_api_delay_range(&self, delay_range: Option<Range<Duration>>) {
         match delay_range {
             Some(range) => {
@@ -514,6 +540,130 @@ impl DirectAccessClient for MemoryClient {
     }
 }
 
+impl MemoryClient {
+    async fn compute_reconstruction_ranges(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<xorb_utils::ReconstructionRangesResult> {
+        let file_info = {
+            let shard = self.shard.read().await;
+            match shard.get_file_reconstruction_info(file_id) {
+                Some(fi) => fi,
+                None => return Ok(None),
+            }
+        };
+
+        let xorbs = self.xorbs.read().await;
+        xorb_utils::compute_reconstruction_ranges(&file_info, bytes_range, &mut |hash| {
+            let storage = xorbs.get(hash).ok_or_else(|| {
+                error!("Unable to find xorb in memory CAS {:?}", hash);
+                CasClientError::XORBNotFound(*hash)
+            })?;
+            Ok(match storage {
+                XorbStorage::Materialized(entry) => entry.xorb_object.clone(),
+                XorbStorage::Random(xorb) => xorb.get_xorb_object(),
+            })
+        })
+    }
+
+    /// V1 reconstruction: returns per-range presigned URLs.
+    pub async fn get_reconstruction_v1(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponse>> {
+        self.apply_api_delay().await;
+
+        let result = self.compute_reconstruction_ranges(file_id, bytes_range).await?;
+        let Some((offset_into_first_range, terms, merged_ranges)) = result else {
+            return Ok(None);
+        };
+
+        if terms.is_empty() {
+            return Ok(Some(QueryReconstructionResponse {
+                offset_into_first_range,
+                terms,
+                fetch_info: HashMap::new(),
+            }));
+        }
+
+        let timestamp = Instant::now();
+        let mut fetch_info: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>> = HashMap::new();
+        for (hash, ranges) in merged_ranges {
+            let entries = ranges
+                .into_iter()
+                .map(|r| XorbReconstructionFetchInfo {
+                    range: r.chunk_range,
+                    url: generate_fetch_url(&hash, &r.byte_range, timestamp),
+                    url_range: HttpRange::from(r.byte_range),
+                })
+                .collect();
+            fetch_info.insert(hash.into(), entries);
+        }
+
+        Ok(Some(QueryReconstructionResponse {
+            offset_into_first_range,
+            terms,
+            fetch_info,
+        }))
+    }
+
+    /// V2 reconstruction: returns per-xorb multi-range fetch descriptors.
+    pub async fn get_reconstruction_v2(
+        &self,
+        file_id: &MerkleHash,
+        bytes_range: Option<FileRange>,
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        self.apply_api_delay().await;
+
+        let result = self.compute_reconstruction_ranges(file_id, bytes_range).await?;
+        let Some((offset_into_first_range, terms, merged_ranges)) = result else {
+            return Ok(None);
+        };
+
+        if terms.is_empty() {
+            return Ok(Some(QueryReconstructionResponseV2 {
+                offset_into_first_range,
+                terms,
+                xorbs: HashMap::new(),
+            }));
+        }
+
+        let timestamp = Instant::now();
+        let max_ranges = self.max_ranges_per_fetch.load(Ordering::Relaxed);
+
+        let mut xorbs: HashMap<HexMerkleHash, Vec<XorbMultiRangeFetch>> = HashMap::new();
+        for (hash, ranges) in merged_ranges {
+            let mut fetch_entries = Vec::new();
+
+            for chunk in ranges.chunks(max_ranges) {
+                let range_descriptors: Vec<XorbRangeDescriptor> = chunk
+                    .iter()
+                    .map(|r| XorbRangeDescriptor {
+                        chunks: r.chunk_range,
+                        bytes: HttpRange::from(r.byte_range),
+                    })
+                    .collect();
+
+                let url = generate_v2_fetch_url(&hash, &range_descriptors, timestamp);
+                fetch_entries.push(XorbMultiRangeFetch {
+                    url,
+                    ranges: range_descriptors,
+                });
+            }
+
+            xorbs.insert(hash.into(), fetch_entries);
+        }
+
+        Ok(Some(QueryReconstructionResponseV2 {
+            offset_into_first_range,
+            terms,
+            xorbs,
+        }))
+    }
+}
+
 #[cfg_attr(not(target_family = "wasm"), async_trait)]
 #[cfg_attr(target_family = "wasm", async_trait(?Send))]
 impl Client for MemoryClient {
@@ -651,194 +801,8 @@ impl Client for MemoryClient {
         &self,
         file_id: &MerkleHash,
         bytes_range: Option<FileRange>,
-    ) -> Result<Option<QueryReconstructionResponse>> {
-        self.apply_api_delay().await;
-        let file_info = {
-            let shard = self.shard.read().await;
-            match shard.get_file_reconstruction_info(file_id) {
-                Some(fi) => fi,
-                None => return Ok(None),
-            }
-        };
-
-        let total_file_size: u64 = file_info.file_size();
-
-        // Handle range validation and truncation
-        let file_range = if let Some(range) = bytes_range {
-            // If the entire range is out of bounds, return None (like RemoteClient does for 416)
-            if range.start >= total_file_size {
-                // For empty files (size 0), only the first query (start == 0) should return the empty reconstruction
-                // All subsequent queries should return None to prevent infinite remainder loops
-                if total_file_size == 0 && range.start == 0 {
-                    // Empty file - return valid but empty reconstruction
-                    return Ok(Some(QueryReconstructionResponse {
-                        offset_into_first_range: 0,
-                        terms: vec![],
-                        fetch_info: HashMap::new(),
-                    }));
-                }
-                return Ok(None);
-            }
-            FileRange::new(range.start, range.end.min(total_file_size))
-        } else {
-            // No range specified - handle empty files
-            if total_file_size == 0 {
-                return Ok(Some(QueryReconstructionResponse {
-                    offset_into_first_range: 0,
-                    terms: vec![],
-                    fetch_info: HashMap::new(),
-                }));
-            }
-            FileRange::full()
-        };
-
-        // Find the first segment that contains bytes in our range
-        let mut s_idx = 0;
-        let mut cumulative_bytes = 0u64;
-        let mut first_chunk_byte_start;
-
-        loop {
-            if s_idx >= file_info.segments.len() {
-                return Err(CasClientError::InvalidRange);
-            }
-
-            let n = file_info.segments[s_idx].unpacked_segment_bytes as u64;
-            if cumulative_bytes + n > file_range.start {
-                assert_ge!(file_range.start, cumulative_bytes);
-                first_chunk_byte_start = cumulative_bytes;
-                break;
-            } else {
-                cumulative_bytes += n;
-                s_idx += 1;
-            }
-        }
-
-        let mut terms = Vec::new();
-
-        #[derive(Clone)]
-        struct FetchInfoIntermediate {
-            chunk_range: ChunkRange,
-            byte_range: FileRange,
-        }
-
-        let mut fetch_info_map: MerkleHashMap<Vec<FetchInfoIntermediate>> = MerkleHashMap::new();
-
-        let xorbs = self.xorbs.read().await;
-
-        while s_idx < file_info.segments.len() && cumulative_bytes < file_range.end {
-            let mut segment = file_info.segments[s_idx].clone();
-            let mut chunk_range = ChunkRange::new(segment.chunk_index_start, segment.chunk_index_end);
-
-            let storage = xorbs.get(&segment.xorb_hash).ok_or_else(|| {
-                error!("Unable to find xorb in memory CAS {:?}", segment.xorb_hash);
-                CasClientError::XORBNotFound(segment.xorb_hash)
-            })?;
-            let xorb_footer = match storage {
-                XorbStorage::Materialized(entry) => entry.xorb_object.clone(),
-                XorbStorage::Random(xorb) => xorb.get_xorb_object(),
-            };
-
-            // Prune first segment on chunk boundaries
-            if cumulative_bytes < file_range.start {
-                while chunk_range.start < chunk_range.end {
-                    let next_chunk_size = xorb_footer.uncompressed_chunk_length(chunk_range.start)? as u64;
-
-                    if cumulative_bytes + next_chunk_size <= file_range.start {
-                        cumulative_bytes += next_chunk_size;
-                        first_chunk_byte_start += next_chunk_size;
-                        segment.unpacked_segment_bytes -= next_chunk_size as u32;
-                        chunk_range.start += 1;
-                        debug_assert_lt!(chunk_range.start, chunk_range.end);
-                    } else {
-                        break;
-                    }
-                }
-            }
-
-            // Prune last segment on chunk boundaries
-            if cumulative_bytes + segment.unpacked_segment_bytes as u64 > file_range.end {
-                while chunk_range.end > chunk_range.start {
-                    let last_chunk_size = xorb_footer.uncompressed_chunk_length(chunk_range.end - 1)?;
-
-                    if cumulative_bytes + (segment.unpacked_segment_bytes - last_chunk_size) as u64 >= file_range.end {
-                        chunk_range.end -= 1;
-                        segment.unpacked_segment_bytes -= last_chunk_size;
-                        debug_assert_lt!(chunk_range.start, chunk_range.end);
-                        assert_gt!(segment.unpacked_segment_bytes, 0);
-                    } else {
-                        break;
-                    }
-                }
-            }
-
-            let (byte_start, byte_end) = xorb_footer.get_byte_offset(chunk_range.start, chunk_range.end)?;
-            let byte_range = FileRange::new(byte_start as u64, byte_end as u64);
-
-            let xorb_reconstruction_term = XorbReconstructionTerm {
-                hash: segment.xorb_hash.into(),
-                unpacked_length: segment.unpacked_segment_bytes,
-                range: chunk_range,
-            };
-
-            terms.push(xorb_reconstruction_term);
-
-            let fetch_info_intermediate = FetchInfoIntermediate {
-                chunk_range,
-                byte_range,
-            };
-
-            fetch_info_map
-                .entry(segment.xorb_hash)
-                .or_default()
-                .push(fetch_info_intermediate);
-
-            cumulative_bytes += segment.unpacked_segment_bytes as u64;
-            s_idx += 1;
-        }
-
-        assert!(!terms.is_empty());
-
-        let timestamp = Instant::now();
-
-        // Sort and merge adjacent/overlapping ranges in each fetch_info Vec
-        let mut merged_fetch_info_map: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>> = HashMap::new();
-        for (hash, mut fi_vec) in fetch_info_map {
-            fi_vec.sort_by_key(|fi| fi.chunk_range.start);
-
-            let mut merged: Vec<XorbReconstructionFetchInfo> = Vec::new();
-            let mut idx = 0;
-
-            while idx < fi_vec.len() {
-                let mut new_fi = fi_vec[idx].clone();
-
-                while idx + 1 < fi_vec.len() {
-                    let next_fi = &fi_vec[idx + 1];
-                    if next_fi.chunk_range.start <= new_fi.chunk_range.end {
-                        new_fi.chunk_range.end = next_fi.chunk_range.end.max(new_fi.chunk_range.end);
-                        new_fi.byte_range.end = next_fi.byte_range.end.max(new_fi.byte_range.end);
-                        idx += 1;
-                    } else {
-                        break;
-                    }
-                }
-
-                merged.push(XorbReconstructionFetchInfo {
-                    range: new_fi.chunk_range,
-                    url: generate_fetch_url(&hash, &new_fi.byte_range, timestamp),
-                    url_range: HttpRange::from(new_fi.byte_range),
-                });
-
-                idx += 1;
-            }
-
-            merged_fetch_info_map.insert(hash.into(), merged);
-        }
-
-        Ok(Some(QueryReconstructionResponse {
-            offset_into_first_range: file_range.start - first_chunk_byte_start,
-            terms,
-            fetch_info: merged_fetch_info_map,
-        }))
+    ) -> Result<Option<QueryReconstructionResponseV2>> {
+        self.get_reconstruction_v2(file_id, bytes_range).await
     }
 
     async fn batch_get_reconstruction(&self, file_ids: &[MerkleHash]) -> Result<BatchQueryReconstructionResponse> {
@@ -847,7 +811,7 @@ impl Client for MemoryClient {
         let mut fetch_info_map: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>> = HashMap::new();
 
         for file_id in file_ids {
-            if let Some(response) = self.get_reconstruction(file_id, None).await? {
+            if let Some(response) = self.get_reconstruction_v1(file_id, None).await? {
                 let hex_hash: HexMerkleHash = (*file_id).into();
                 files.insert(hex_hash, response.terms);
 
@@ -876,8 +840,8 @@ impl Client for MemoryClient {
         uncompressed_size_if_known: Option<usize>,
     ) -> Result<(Bytes, Vec<u32>)> {
         self.apply_api_delay().await;
-        let (url, range) = url_info.retrieve_url().await?;
-        let (xorb_hash, _url_byte_range, url_timestamp) = parse_fetch_url(&url)?;
+        let (url, http_ranges) = url_info.retrieve_url().await?;
+        let (xorb_hash, url_timestamp) = parse_any_fetch_url(&url)?;
 
         // Check if URL has expired
         let expiration_ms = self.url_expiration_ms.load(Ordering::Relaxed);
@@ -889,12 +853,17 @@ impl Client for MemoryClient {
         let xorbs = self.xorbs.read().await;
         let storage = xorbs.get(&xorb_hash).ok_or(CasClientError::XORBNotFound(xorb_hash))?;
 
-        // Extract the byte range from the serialized data and deserialize
-        let start = range.start as usize;
-        let end = range.end as usize + 1; // HttpRange is inclusive end
-        let transfer_len = (end - start) as u64;
+        // Extract each byte range from the serialized data and deserialize
+        let mut all_decompressed = Vec::new();
+        let mut all_chunk_indices = Vec::<u32>::new();
+        let mut total_transfer = 0u64;
 
-        let (decompressed_data, chunk_byte_indices) = match storage {
+        for http_range in &http_ranges {
+            let start = http_range.start as usize;
+            let end = http_range.end as usize + 1;
+            total_transfer += http_range.length();
+
+            let (data, chunk_indices) = match storage {
                 XorbStorage::Materialized(entry) => {
                     let range_data = &entry.serialized_data[start..end];
                     xet_core_structures::xorb_object::deserialize_chunks(&mut Cursor::new(range_data))?
@@ -905,20 +874,28 @@ impl Client for MemoryClient {
                 },
             };
 
+            xet_core_structures::xorb_object::append_chunk_segment(
+                &mut all_decompressed,
+                &mut all_chunk_indices,
+                &data,
+                &chunk_indices,
+            );
+        }
+
         if let Some(expected) = uncompressed_size_if_known {
             debug_assert_eq!(
-                decompressed_data.len(),
+                all_decompressed.len(),
                 expected,
                 "get_file_term_data: expected {} bytes, got {}",
                 expected,
-                decompressed_data.len()
+                all_decompressed.len()
             );
         }
 
         if let Some(ref cb) = progress_callback {
-            cb(transfer_len, transfer_len, transfer_len);
+            cb(total_transfer, total_transfer, total_transfer);
         }
-        Ok((Bytes::from(decompressed_data), chunk_byte_indices))
+        Ok((Bytes::from(all_decompressed), all_chunk_indices))
     }
 }
 
@@ -946,6 +923,19 @@ fn parse_fetch_url(url: &str) -> Result<(MerkleHash, FileRange, Instant)> {
     Ok((hash, byte_range, timestamp))
 }
 
+fn generate_v2_fetch_url(hash: &MerkleHash, ranges: &[XorbRangeDescriptor], timestamp: Instant) -> String {
+    xorb_utils::generate_v2_fetch_url(hash, ranges, timestamp)
+}
+
+/// Parse either a V1 or V2 fetch URL, returning (hash, timestamp).
+fn parse_any_fetch_url(url: &str) -> Result<(MerkleHash, Instant)> {
+    if let Ok((hash, _, ts)) = parse_fetch_url(url) {
+        return Ok((hash, ts));
+    }
+    let (hash, ts, _) = xorb_utils::parse_v2_fetch_url(url)?;
+    Ok((hash, ts))
+}
+
 #[cfg(all(test, not(target_family = "wasm")))]
 mod tests {
     use super::super::client_testing_utils::ClientTestingUtils;
@@ -1062,7 +1052,7 @@ mod tests {
         assert_eq!(range_data.as_ref(), &file2.data[start as usize..end as usize]);
 
         // Reconstruction workflow
-        let recon = client.get_reconstruction(&file2.file_hash, None).await.unwrap().unwrap();
+        let recon = client.get_reconstruction_v1(&file2.file_hash, None).await.unwrap().unwrap();
         for term in &recon.terms {
             let xorb_hash: MerkleHash = term.hash.into();
             for fetch_info in recon.fetch_info.get(&term.hash).unwrap() {

xet_client/src/cas_client/simulation/mod.rs

@@ -34,6 +34,7 @@ mod simulation_server;
 #[cfg(unix)]
 #[cfg(not(target_family = "wasm"))]
 pub mod socket_proxy;
+pub(crate) mod xorb_utils;
 
 pub use client_testing_utils::{ClientTestingUtils, RandomFileContents};
 #[cfg(not(target_family = "wasm"))]

xet_client/src/cas_client/simulation/simulation_client.rs

@@ -132,7 +132,7 @@ impl Client for RemoteSimulationClient {
         &self,
         file_id: &xet_core_structures::merklehash::MerkleHash,
         bytes_range: Option<crate::cas_types::FileRange>,
-    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponseV2>> {
         self.inner.get_reconstruction(file_id, bytes_range).await
     }
 

xet_client/src/cas_client/simulation/simulation_server.rs

@@ -440,7 +440,7 @@ impl Client for LocalTestServer {
         &self,
         file_id: &xet_core_structures::merklehash::MerkleHash,
         bytes_range: Option<crate::cas_types::FileRange>,
-    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponseV2>> {
         self.remote_simulation_client.get_reconstruction(file_id, bytes_range).await
     }
 
@@ -512,6 +512,30 @@ impl DirectAccessClient for LocalTestServer {
         self.client.set_api_delay_range(delay_range);
     }
 
+    fn set_max_ranges_per_fetch(&self, max_ranges: usize) {
+        self.client.set_max_ranges_per_fetch(max_ranges);
+    }
+
+    fn disable_v2_reconstruction(&self, status_code: u16) {
+        self.client.disable_v2_reconstruction(status_code);
+    }
+
+    async fn get_reconstruction_v1(
+        &self,
+        file_id: &xet_core_structures::merklehash::MerkleHash,
+        bytes_range: Option<crate::cas_types::FileRange>,
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponse>> {
+        self.client.get_reconstruction_v1(file_id, bytes_range).await
+    }
+
+    async fn get_reconstruction_v2(
+        &self,
+        file_id: &xet_core_structures::merklehash::MerkleHash,
+        bytes_range: Option<crate::cas_types::FileRange>,
+    ) -> Result<Option<crate::cas_types::QueryReconstructionResponseV2>> {
+        self.client.get_reconstruction_v2(file_id, bytes_range).await
+    }
+
     async fn apply_api_delay(&self) {
         self.client.apply_api_delay().await;
     }
@@ -690,31 +714,22 @@ mod tests {
 
         // Fetch term endpoint - verify URLs are HTTP and data can be fetched
         let http_client = reqwest::Client::new();
-        for fetch_infos in remote_recon.fetch_info.values() {
-            for fi in fetch_infos {
-                assert!(fi.url.starts_with("http://"));
-                assert!(fi.url.contains("/fetch_term?term="));
-                let response = http_client.get(&fi.url).send().await.unwrap();
+        for multi_range_fetches in remote_recon.xorbs.values() {
+            for mrf in multi_range_fetches {
+                assert!(mrf.url.starts_with("http://"));
+                assert!(mrf.url.contains("/fetch_term?term="));
+                let response = http_client.get(&mrf.url).send().await.unwrap();
                 assert!(response.status().is_success());
                 assert!(!response.bytes().await.unwrap().is_empty());
             }
         }
 
-        // Fetch term with range request
-        let first_fi = &remote_recon.fetch_info.values().next().unwrap()[0];
-        let full_data = http_client.get(&first_fi.url).send().await.unwrap().bytes().await.unwrap();
-        if full_data.len() > 100 {
-            let range_resp = http_client
-                .get(&first_fi.url)
-                .header(reqwest::header::RANGE, "bytes=0-99")
-                .send()
-                .await
-                .unwrap();
-            assert!(range_resp.status().is_success());
-            let range_data = range_resp.bytes().await.unwrap();
-            assert_eq!(range_data.len(), 100);
-            assert_eq!(&range_data[..], &full_data[..100]);
-        }
+        // Verify V2 fetch URLs return consistent data across multiple requests.
+        let first_mrf = &remote_recon.xorbs.values().next().unwrap()[0];
+        let data_1 = http_client.get(&first_mrf.url).send().await.unwrap().bytes().await.unwrap();
+        let data_2 = http_client.get(&first_mrf.url).send().await.unwrap().bytes().await.unwrap();
+        assert_eq!(data_1, data_2);
+        assert!(!data_1.is_empty());
     }
 
     /// Tests that invalid requests return appropriate error responses.
@@ -762,16 +777,16 @@ mod tests {
             .await
             .unwrap()
             .unwrap();
-        for (hash, fetch_infos) in &recon1.fetch_info {
-            for fi in fetch_infos {
+        for (hash, multi_range_fetches) in &recon1.xorbs {
+            for mrf in multi_range_fetches {
                 assert!(
-                    fi.url.starts_with("http://") || fi.url.starts_with("https://"),
+                    mrf.url.starts_with("http://") || mrf.url.starts_with("https://"),
                     "URL for hash {} should be HTTP, got: {}",
                     hash,
-                    fi.url
+                    mrf.url
                 );
-                assert!(fi.url.contains("/fetch_term?term="));
-                assert!(!fi.url.contains("\":"));
+                assert!(mrf.url.contains("/fetch_term?term="));
+                assert!(!mrf.url.contains("\":"));
             }
         }
 
@@ -782,10 +797,10 @@ mod tests {
             .await
             .unwrap()
             .unwrap();
-        assert!(multi_recon.fetch_info.len() >= 2);
-        for fetch_infos in multi_recon.fetch_info.values() {
-            for fi in fetch_infos {
-                assert!(fi.url.starts_with("http://"));
+        assert!(multi_recon.xorbs.len() >= 2);
+        for multi_range_fetches in multi_recon.xorbs.values() {
+            for mrf in multi_range_fetches {
+                assert!(mrf.url.starts_with("http://"));
             }
         }
 
@@ -798,18 +813,18 @@ mod tests {
             .await
             .unwrap()
             .unwrap();
-        for fetch_infos in range_recon.fetch_info.values() {
-            for fi in fetch_infos {
-                assert!(fi.url.starts_with("http://"));
-                assert!(fi.url.contains("/fetch_term?term="));
+        for multi_range_fetches in range_recon.xorbs.values() {
+            for mrf in multi_range_fetches {
+                assert!(mrf.url.starts_with("http://"));
+                assert!(mrf.url.contains("/fetch_term?term="));
             }
         }
 
         // Verify all term URLs are fetchable
         for term in &recon1.terms {
-            let fetch_infos = recon1.fetch_info.get(&term.hash).unwrap();
-            for fi in fetch_infos {
-                let response = http_client.get(&fi.url).send().await.unwrap();
+            let multi_range_fetches = recon1.xorbs.get(&term.hash).unwrap();
+            for mrf in multi_range_fetches {
+                let response = http_client.get(&mrf.url).send().await.unwrap();
                 assert!(response.status().is_success());
                 assert!(!response.bytes().await.unwrap().is_empty());
             }
@@ -860,9 +875,9 @@ mod tests {
             let expected_term = &file.terms[term_idx];
             assert_eq!(recon_term.hash.0, expected_term.xorb_hash);
 
-            // Verify fetch_info exists for each XORB
-            let fetch_infos = recon.fetch_info.get(&recon_term.hash).unwrap();
-            assert!(!fetch_infos.is_empty());
+            // Verify xorbs has entry for each term
+            let multi_range_fetches = recon.xorbs.get(&recon_term.hash).unwrap();
+            assert!(!multi_range_fetches.is_empty());
         }
 
         // Verify the complete file can be retrieved correctly via LocalClient

xet_client/src/cas_client/simulation/xorb_utils.rs

@@ -0,0 +1,499 @@
+//! Shared utilities for reconstruction range computation and V2 URL encoding.
+//!
+//! This module consolidates logic used by both `MemoryClient` and `LocalClient`
+//! for computing reconstruction ranges from file segment info, merging adjacent
+//! ranges, and encoding/decoding V2 fetch URLs.
+
+use base64::Engine;
+use base64::engine::general_purpose::URL_SAFE_NO_PAD;
+use more_asserts::{assert_ge, assert_gt, debug_assert_lt};
+use tokio::time::{Duration, Instant};
+use xet_core_structures::MerkleHashMap;
+use xet_core_structures::merklehash::MerkleHash;
+use xet_core_structures::metadata_shard::file_structs::MDBFileInfo;
+use xet_core_structures::xorb_object::XorbObject;
+
+use crate::cas_client::error::{CasClientError, Result};
+use crate::cas_types::{ChunkRange, FileRange, HttpRange, XorbRangeDescriptor, XorbReconstructionTerm};
+
+lazy_static::lazy_static! {
+    /// Reference instant for URL timestamps. Initialized far in the past to allow
+    /// testing timestamps that are earlier in the current process lifetime.
+    pub(crate) static ref REFERENCE_INSTANT: Instant = {
+        let now = Instant::now();
+        now.checked_sub(Duration::from_secs(365 * 24 * 60 * 60))
+            .unwrap_or(now)
+    };
+}
+
+/// A merged byte/chunk range for a single xorb.
+#[derive(Clone, Debug)]
+pub(crate) struct MergedRange {
+    pub chunk_range: ChunkRange,
+    pub byte_range: FileRange,
+}
+
+/// Result of `compute_reconstruction_ranges`: the offset into the first range,
+/// the list of reconstruction terms, and the merged ranges per xorb hash.
+pub(crate) type ReconstructionRangesResult =
+    Option<(u64, Vec<XorbReconstructionTerm>, MerkleHashMap<Vec<MergedRange>>)>;
+
+/// Computes reconstruction ranges from file segment info.
+///
+/// Iterates the segments in `file_info`, prunes chunk boundaries to the
+/// requested `bytes_range`, and merges adjacent/overlapping ranges per xorb.
+///
+/// `get_xorb_footer` is called for each unique xorb hash encountered to obtain
+/// the `XorbObject` metadata needed for chunk-level byte offset calculations.
+///
+/// Returns `Ok(None)` when the range is out of bounds, or
+/// `Ok(Some((offset_into_first_range, terms, merged_ranges_per_xorb)))`.
+pub(crate) fn compute_reconstruction_ranges(
+    file_info: &MDBFileInfo,
+    bytes_range: Option<FileRange>,
+    get_xorb_footer: &mut dyn FnMut(&MerkleHash) -> Result<XorbObject>,
+) -> Result<ReconstructionRangesResult> {
+    let total_file_size: u64 = file_info.file_size();
+
+    let file_range = if let Some(range) = bytes_range {
+        if range.start >= total_file_size {
+            if total_file_size == 0 && range.start == 0 {
+                return Ok(Some((0, vec![], MerkleHashMap::new())));
+            }
+            return Ok(None);
+        }
+        FileRange::new(range.start, range.end.min(total_file_size))
+    } else {
+        if total_file_size == 0 {
+            return Ok(Some((0, vec![], MerkleHashMap::new())));
+        }
+        FileRange::full()
+    };
+
+    let mut s_idx = 0;
+    let mut cumulative_bytes = 0u64;
+    let mut first_chunk_byte_start;
+
+    loop {
+        if s_idx >= file_info.segments.len() {
+            return Err(CasClientError::InvalidRange);
+        }
+
+        let n = file_info.segments[s_idx].unpacked_segment_bytes as u64;
+        if cumulative_bytes + n > file_range.start {
+            assert_ge!(file_range.start, cumulative_bytes);
+            first_chunk_byte_start = cumulative_bytes;
+            break;
+        } else {
+            cumulative_bytes += n;
+            s_idx += 1;
+        }
+    }
+
+    let mut terms = Vec::new();
+
+    #[derive(Clone)]
+    struct FetchInfoIntermediate {
+        chunk_range: ChunkRange,
+        byte_range: FileRange,
+    }
+
+    let mut fetch_info_map: MerkleHashMap<Vec<FetchInfoIntermediate>> = MerkleHashMap::new();
+
+    while s_idx < file_info.segments.len() && cumulative_bytes < file_range.end {
+        let mut segment = file_info.segments[s_idx].clone();
+        let mut chunk_range = ChunkRange::new(segment.chunk_index_start, segment.chunk_index_end);
+
+        let xorb_footer = get_xorb_footer(&segment.xorb_hash)?;
+
+        if cumulative_bytes < file_range.start {
+            while chunk_range.start < chunk_range.end {
+                let next_chunk_size = xorb_footer.uncompressed_chunk_length(chunk_range.start)? as u64;
+                if cumulative_bytes + next_chunk_size <= file_range.start {
+                    cumulative_bytes += next_chunk_size;
+                    first_chunk_byte_start += next_chunk_size;
+                    segment.unpacked_segment_bytes -= next_chunk_size as u32;
+                    chunk_range.start += 1;
+                    debug_assert_lt!(chunk_range.start, chunk_range.end);
+                } else {
+                    break;
+                }
+            }
+        }
+
+        if cumulative_bytes + segment.unpacked_segment_bytes as u64 > file_range.end {
+            while chunk_range.end > chunk_range.start {
+                let last_chunk_size = xorb_footer.uncompressed_chunk_length(chunk_range.end - 1)?;
+                if cumulative_bytes + (segment.unpacked_segment_bytes - last_chunk_size) as u64 >= file_range.end {
+                    chunk_range.end -= 1;
+                    segment.unpacked_segment_bytes -= last_chunk_size;
+                    debug_assert_lt!(chunk_range.start, chunk_range.end);
+                    assert_gt!(segment.unpacked_segment_bytes, 0);
+                } else {
+                    break;
+                }
+            }
+        }
+
+        let (byte_start, byte_end) = xorb_footer.get_byte_offset(chunk_range.start, chunk_range.end)?;
+        let byte_range = FileRange::new(byte_start as u64, byte_end as u64);
+
+        terms.push(XorbReconstructionTerm {
+            hash: segment.xorb_hash.into(),
+            unpacked_length: segment.unpacked_segment_bytes,
+            range: chunk_range,
+        });
+
+        fetch_info_map
+            .entry(segment.xorb_hash)
+            .or_default()
+            .push(FetchInfoIntermediate {
+                chunk_range,
+                byte_range,
+            });
+
+        cumulative_bytes += segment.unpacked_segment_bytes as u64;
+        s_idx += 1;
+    }
+
+    debug_assert!(!terms.is_empty());
+
+    let mut merged: MerkleHashMap<Vec<MergedRange>> = MerkleHashMap::new();
+    for (hash, mut fi_vec) in fetch_info_map {
+        fi_vec.sort_by_key(|fi| fi.chunk_range.start);
+
+        let mut result: Vec<MergedRange> = Vec::new();
+        let mut idx = 0;
+
+        while idx < fi_vec.len() {
+            let mut cur = fi_vec[idx].clone();
+
+            while idx + 1 < fi_vec.len() {
+                let next = &fi_vec[idx + 1];
+                if next.chunk_range.start <= cur.chunk_range.end {
+                    cur.chunk_range.end = cur.chunk_range.end.max(next.chunk_range.end);
+                    cur.byte_range.end = cur.byte_range.end.max(next.byte_range.end);
+                    idx += 1;
+                } else {
+                    break;
+                }
+            }
+
+            result.push(MergedRange {
+                chunk_range: cur.chunk_range,
+                byte_range: cur.byte_range,
+            });
+            idx += 1;
+        }
+
+        merged.insert(hash, result);
+    }
+
+    Ok(Some((file_range.start - first_chunk_byte_start, terms, merged)))
+}
+
+/// Generates a V2 fetch URL: base64("{hash_hex}:{timestamp_ms}:{r1_start}-{r1_end},...")
+pub(crate) fn generate_v2_fetch_url(hash: &MerkleHash, ranges: &[XorbRangeDescriptor], timestamp: Instant) -> String {
+    let timestamp_ms = timestamp.saturating_duration_since(*REFERENCE_INSTANT).as_millis() as u64;
+    let ranges_str: Vec<String> = ranges.iter().map(|r| format!("{}-{}", r.bytes.start, r.bytes.end)).collect();
+    let payload = format!("{}:{}:{}", hash.hex(), timestamp_ms, ranges_str.join(","));
+    URL_SAFE_NO_PAD.encode(payload.as_bytes())
+}
+
+/// Parses a V2 fetch URL back into (hash, timestamp, byte ranges).
+pub(crate) fn parse_v2_fetch_url(url: &str) -> Result<(MerkleHash, Instant, Vec<HttpRange>)> {
+    let bytes = URL_SAFE_NO_PAD.decode(url).map_err(|_| CasClientError::InvalidArguments)?;
+    let payload = String::from_utf8(bytes).map_err(|_| CasClientError::InvalidArguments)?;
+
+    let mut parts = payload.splitn(3, ':');
+    let hash_hex = parts.next().ok_or(CasClientError::InvalidArguments)?;
+    let ts_str = parts.next().ok_or(CasClientError::InvalidArguments)?;
+    let ranges_str = parts.next().ok_or(CasClientError::InvalidArguments)?;
+
+    let hash = MerkleHash::from_hex(hash_hex).map_err(|_| CasClientError::InvalidArguments)?;
+    let timestamp_ms: u64 = ts_str.parse().map_err(|_| CasClientError::InvalidArguments)?;
+    let timestamp = *REFERENCE_INSTANT + Duration::from_millis(timestamp_ms);
+
+    let mut ranges = Vec::new();
+    for r in ranges_str.split(',').filter(|s| !s.is_empty()) {
+        let mut parts = r.splitn(2, '-');
+        let start: u64 = parts
+            .next()
+            .ok_or(CasClientError::InvalidArguments)?
+            .parse()
+            .map_err(|_| CasClientError::InvalidArguments)?;
+        let end: u64 = parts
+            .next()
+            .ok_or(CasClientError::InvalidArguments)?
+            .parse()
+            .map_err(|_| CasClientError::InvalidArguments)?;
+        ranges.push(HttpRange::new(start, end));
+    }
+
+    Ok((hash, timestamp, ranges))
+}
+
+#[cfg(test)]
+mod tests {
+    use xet_core_structures::metadata_shard::file_structs::{
+        FileDataSequenceEntry, FileDataSequenceHeader, MDBFileInfo,
+    };
+
+    use super::super::random_xorb::RandomXorb;
+    use super::*;
+
+    fn make_range_descriptor(chunk_start: u32, chunk_end: u32, byte_start: u64, byte_end: u64) -> XorbRangeDescriptor {
+        XorbRangeDescriptor {
+            chunks: ChunkRange::new(chunk_start, chunk_end),
+            bytes: HttpRange::new(byte_start, byte_end),
+        }
+    }
+
+    fn build_xorb(chunk_sizes: &[usize]) -> (MerkleHash, XorbObject) {
+        let seed_and_sizes: Vec<(u64, u32)> =
+            chunk_sizes.iter().enumerate().map(|(i, &s)| (i as u64, s as u32)).collect();
+        let xorb = RandomXorb::new(&seed_and_sizes);
+        let xorb_object = xorb.get_xorb_object();
+        let hash = xorb.xorb_hash();
+        (hash, xorb_object)
+    }
+
+    fn make_segment(
+        xorb_hash: MerkleHash,
+        chunk_start: u32,
+        chunk_end: u32,
+        unpacked_bytes: u32,
+    ) -> FileDataSequenceEntry {
+        FileDataSequenceEntry {
+            xorb_hash,
+            xorb_flags: 0,
+            chunk_index_start: chunk_start,
+            chunk_index_end: chunk_end,
+            unpacked_segment_bytes: unpacked_bytes,
+        }
+    }
+
+    fn make_file_info(segments: Vec<FileDataSequenceEntry>) -> MDBFileInfo {
+        MDBFileInfo {
+            metadata: FileDataSequenceHeader {
+                file_hash: MerkleHash::default(),
+                ..Default::default()
+            },
+            segments,
+            verification: vec![],
+            metadata_ext: None,
+        }
+    }
+
+    #[test]
+    fn test_v2_url_roundtrip() {
+        let hash = MerkleHash::from_hex("a32d3a2a2e83e4d41b04899f13a8e891f4dd3f2ed940f96f91da7bf55b7ee299").unwrap();
+        let ranges = vec![
+            make_range_descriptor(0, 3, 0, 1024),
+            make_range_descriptor(5, 8, 2048, 4096),
+        ];
+        let timestamp = Instant::now();
+
+        let url = generate_v2_fetch_url(&hash, &ranges, timestamp);
+        let (parsed_hash, parsed_ts, parsed_ranges) = parse_v2_fetch_url(&url).unwrap();
+
+        assert_eq!(hash, parsed_hash);
+        assert_eq!(parsed_ranges.len(), 2);
+        assert_eq!(parsed_ranges[0].start, 0);
+        assert_eq!(parsed_ranges[0].end, 1024);
+        assert_eq!(parsed_ranges[1].start, 2048);
+        assert_eq!(parsed_ranges[1].end, 4096);
+
+        let diff = if parsed_ts > timestamp {
+            parsed_ts - timestamp
+        } else {
+            timestamp - parsed_ts
+        };
+        assert!(diff < Duration::from_millis(2));
+    }
+
+    #[test]
+    fn test_v2_url_single_range() {
+        let hash = MerkleHash::default();
+        let ranges = vec![make_range_descriptor(0, 1, 100, 200)];
+        let timestamp = Instant::now();
+
+        let url = generate_v2_fetch_url(&hash, &ranges, timestamp);
+        let (_, _, parsed_ranges) = parse_v2_fetch_url(&url).unwrap();
+
+        assert_eq!(parsed_ranges.len(), 1);
+        assert_eq!(parsed_ranges[0].start, 100);
+        assert_eq!(parsed_ranges[0].end, 200);
+    }
+
+    #[test]
+    fn test_v2_url_invalid_base64() {
+        assert!(parse_v2_fetch_url("not-valid!!!").is_err());
+    }
+
+    #[test]
+    fn test_v2_url_invalid_payload() {
+        let url = URL_SAFE_NO_PAD.encode(b"bad");
+        assert!(parse_v2_fetch_url(&url).is_err());
+    }
+
+    #[test]
+    fn test_compute_ranges_single_segment() {
+        let (xorb_hash, xorb_object) = build_xorb(&[100, 200, 300]);
+        let file_info = make_file_info(vec![make_segment(xorb_hash, 0, 3, 600)]);
+
+        let result = compute_reconstruction_ranges(&file_info, None, &mut |_| Ok(xorb_object.clone())).unwrap();
+        let (offset, terms, merged) = result.unwrap();
+
+        assert_eq!(offset, 0);
+        assert_eq!(terms.len(), 1);
+        assert_eq!(terms[0].unpacked_length, 600);
+        assert_eq!(terms[0].range.start, 0);
+        assert_eq!(terms[0].range.end, 3);
+
+        let xorb_ranges = merged.get(&xorb_hash).unwrap();
+        assert_eq!(xorb_ranges.len(), 1);
+        assert_eq!(xorb_ranges[0].chunk_range.start, 0);
+        assert_eq!(xorb_ranges[0].chunk_range.end, 3);
+    }
+
+    #[test]
+    fn test_compute_ranges_partial_range() {
+        let (xorb_hash, xorb_object) = build_xorb(&[100, 200, 300]);
+        let file_info = make_file_info(vec![make_segment(xorb_hash, 0, 3, 600)]);
+
+        let range = FileRange::new(100, 300);
+        let result = compute_reconstruction_ranges(&file_info, Some(range), &mut |_| Ok(xorb_object.clone())).unwrap();
+        let (offset, terms, merged) = result.unwrap();
+
+        assert_eq!(offset, 0, "range starts exactly at chunk boundary");
+        assert_eq!(terms.len(), 1);
+        assert_eq!(terms[0].range.start, 1);
+        assert_eq!(terms[0].range.end, 2);
+        assert_eq!(terms[0].unpacked_length, 200);
+
+        let xorb_ranges = merged.get(&xorb_hash).unwrap();
+        assert_eq!(xorb_ranges.len(), 1);
+        assert_eq!(xorb_ranges[0].chunk_range.start, 1);
+        assert_eq!(xorb_ranges[0].chunk_range.end, 2);
+    }
+
+    #[test]
+    fn test_compute_ranges_out_of_bounds() {
+        let file_info = make_file_info(vec![make_segment(MerkleHash::default(), 0, 1, 100)]);
+
+        let range = FileRange::new(200, 300);
+        let result = compute_reconstruction_ranges(&file_info, Some(range), &mut |_| {
+            panic!("should not be called for out-of-range")
+        })
+        .unwrap();
+        assert!(result.is_none());
+    }
+
+    #[test]
+    fn test_compute_ranges_empty_file() {
+        let file_info = make_file_info(vec![]);
+
+        let result =
+            compute_reconstruction_ranges(&file_info, None, &mut |_| panic!("should not be called for empty file"))
+                .unwrap();
+        let (offset, terms, merged) = result.unwrap();
+        assert_eq!(offset, 0);
+        assert!(terms.is_empty());
+        assert!(merged.is_empty());
+
+        let result = compute_reconstruction_ranges(&file_info, Some(FileRange::new(0, 100)), &mut |_| {
+            panic!("should not be called for empty file")
+        })
+        .unwrap();
+        let (offset, terms, _) = result.unwrap();
+        assert_eq!(offset, 0);
+        assert!(terms.is_empty());
+
+        let result = compute_reconstruction_ranges(&file_info, Some(FileRange::new(1, 100)), &mut |_| {
+            panic!("should not be called for empty file")
+        })
+        .unwrap();
+        assert!(result.is_none());
+    }
+
+    #[test]
+    fn test_compute_ranges_merges_adjacent() {
+        let (xorb_hash, xorb_object) = build_xorb(&[100, 100, 100, 100]);
+        let file_info = make_file_info(vec![make_segment(xorb_hash, 0, 2, 200), make_segment(xorb_hash, 2, 4, 200)]);
+
+        let result = compute_reconstruction_ranges(&file_info, None, &mut |_| Ok(xorb_object.clone())).unwrap();
+        let (offset, terms, merged) = result.unwrap();
+
+        assert_eq!(offset, 0);
+        assert_eq!(terms.len(), 2);
+
+        let xorb_ranges = merged.get(&xorb_hash).unwrap();
+        assert_eq!(xorb_ranges.len(), 1);
+        assert_eq!(xorb_ranges[0].chunk_range.start, 0);
+        assert_eq!(xorb_ranges[0].chunk_range.end, 4);
+    }
+
+    #[test]
+    fn test_compute_ranges_multi_xorb_non_contiguous() {
+        let (hash_a, obj_a) = build_xorb(&[100, 100, 100, 100]);
+        let (hash_b, obj_b) = build_xorb(&[150, 150]);
+
+        let file_info = make_file_info(vec![
+            make_segment(hash_a, 0, 2, 200),
+            make_segment(hash_b, 0, 2, 300),
+            make_segment(hash_a, 2, 4, 200),
+        ]);
+
+        let result = compute_reconstruction_ranges(&file_info, None, &mut |hash| {
+            if *hash == hash_a {
+                Ok(obj_a.clone())
+            } else if *hash == hash_b {
+                Ok(obj_b.clone())
+            } else {
+                Err(CasClientError::XORBNotFound(*hash))
+            }
+        })
+        .unwrap();
+
+        let (offset, terms, merged) = result.unwrap();
+        assert_eq!(offset, 0);
+        assert_eq!(terms.len(), 3);
+
+        let a_ranges = merged.get(&hash_a).unwrap();
+        assert_eq!(a_ranges.len(), 1);
+        assert_eq!(a_ranges[0].chunk_range.start, 0);
+        assert_eq!(a_ranges[0].chunk_range.end, 4);
+
+        let b_ranges = merged.get(&hash_b).unwrap();
+        assert_eq!(b_ranges.len(), 1);
+        assert_eq!(b_ranges[0].chunk_range.start, 0);
+        assert_eq!(b_ranges[0].chunk_range.end, 2);
+    }
+
+    #[test]
+    fn test_compute_ranges_truncates_to_file_size() {
+        let (xorb_hash, xorb_object) = build_xorb(&[500]);
+        let file_info = make_file_info(vec![make_segment(xorb_hash, 0, 1, 500)]);
+
+        let range = FileRange::new(0, 10000);
+        let result = compute_reconstruction_ranges(&file_info, Some(range), &mut |_| Ok(xorb_object.clone())).unwrap();
+        let (offset, terms, _) = result.unwrap();
+        assert_eq!(offset, 0);
+        assert_eq!(terms.len(), 1);
+        assert_eq!(terms[0].unpacked_length, 500);
+    }
+
+    #[test]
+    fn test_compute_ranges_offset_into_first_range() {
+        let (xorb_hash, xorb_object) = build_xorb(&[100, 200, 300]);
+        let file_info = make_file_info(vec![make_segment(xorb_hash, 0, 3, 600)]);
+
+        let range = FileRange::new(150, 600);
+        let result = compute_reconstruction_ranges(&file_info, Some(range), &mut |_| Ok(xorb_object.clone())).unwrap();
+        let (offset, terms, _) = result.unwrap();
+
+        assert_eq!(offset, 50);
+        assert_eq!(terms[0].range.start, 1);
+    }
+}

xet_client/src/cas_types/mod.rs

@@ -217,6 +217,66 @@ pub struct QueryReconstructionResponse {
     pub fetch_info: HashMap<HexMerkleHash, Vec<XorbReconstructionFetchInfo>>,
 }
 
+/// V2 reconstruction response - optimized for multi-range fetching.
+/// May provide fewer signed URLs per xorb by combining multiple byte ranges
+/// into a single URL where possible.
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub struct QueryReconstructionResponseV2 {
+    pub offset_into_first_range: u64,
+    pub terms: Vec<XorbReconstructionTerm>,
+    /// Map from xorb hash -> list of multi-range fetch entries.
+    /// Typically 1 entry per xorb. Multiple entries when the URL length limit
+    /// (~8 KiB, roughly ~500 ranges) forces a split.
+    pub xorbs: HashMap<HexMerkleHash, Vec<XorbMultiRangeFetch>>,
+}
+
+/// A signed multi-range fetch: one URL covering a subset of ranges for a xorb.
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub struct XorbMultiRangeFetch {
+    /// Signed URL with all byte ranges encoded. Client must send exactly the
+    /// signed range value as the Range header.
+    pub url: String,
+    /// Byte ranges covered by this URL, sorted by chunk start.
+    pub ranges: Vec<XorbRangeDescriptor>,
+}
+
+/// A single byte range within a xorb, mapping chunk indices to physical bytes.
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub struct XorbRangeDescriptor {
+    /// Chunk index range [start, end) within the xorb.
+    pub chunks: ChunkRange,
+    /// Physical byte range [start, end] (inclusive end) for the HTTP Range header.
+    pub bytes: HttpRange,
+}
+
+impl From<QueryReconstructionResponse> for QueryReconstructionResponseV2 {
+    fn from(v1: QueryReconstructionResponse) -> Self {
+        let xorbs = v1
+            .fetch_info
+            .into_iter()
+            .map(|(hash, fetch_infos)| {
+                let fetch = fetch_infos
+                    .into_iter()
+                    .map(|info| XorbMultiRangeFetch {
+                        url: info.url,
+                        ranges: vec![XorbRangeDescriptor {
+                            chunks: info.range,
+                            bytes: info.url_range,
+                        }],
+                    })
+                    .collect();
+                (hash, fetch)
+            })
+            .collect();
+
+        QueryReconstructionResponseV2 {
+            offset_into_first_range: v1.offset_into_first_range,
+            terms: v1.terms,
+            xorbs,
+        }
+    }
+}
+
 // Request json body type representation for the POST /reconstructions endpoint
 // to get the reconstruction for multiple files at a time.
 // listing of non-duplicate (enforced by HashSet) keys (file ids) to get reconstructions for

xet_client/tests/test_shard_upload_timeout.rs

@@ -0,0 +1,40 @@
+//! Integration tests for the shard upload no-read-timeout client (XET-885).
+//!
+//! Verifies that shard uploads succeed even when the server takes a long time to process,
+//! since the shard upload client has no read_timeout.
+
+use std::time::Duration;
+
+use xet_client::cas_client::simulation::ClientTestingUtils;
+use xet_client::cas_client::{DirectAccessClient, LocalTestServerBuilder};
+use xet_runtime::test_set_config;
+
+test_set_config! {
+    client {
+        retry_max_attempts = 1usize;
+        retry_base_delay = Duration::from_millis(10);
+    }
+}
+
+const CHUNK_SIZE: usize = 123;
+
+#[tokio::test]
+async fn test_shard_upload_succeeds_with_no_server_delay() {
+    let server = LocalTestServerBuilder::new().start().await;
+
+    let result = server.remote_client().upload_random_file(&[(1, (0, 5))], CHUNK_SIZE).await;
+
+    assert!(result.is_ok(), "Shard upload should succeed with no server delay: {result:?}");
+}
+
+#[tokio::test]
+async fn test_shard_upload_succeeds_with_slow_server() {
+    let server = LocalTestServerBuilder::new().start().await;
+
+    // Server takes 3s to respond — shard upload client has no read_timeout so this should succeed
+    server.set_api_delay_range(Some(Duration::from_secs(3)..Duration::from_secs(3)));
+
+    let result = server.remote_client().upload_random_file(&[(1, (0, 5))], CHUNK_SIZE).await;
+
+    assert!(result.is_ok(), "Shard upload should succeed even with slow server (no read_timeout): {result:?}");
+}

xet_core_structures/src/xorb_object/xorb_chunk_format.rs

@@ -192,6 +192,27 @@ pub fn deserialize_chunks<R: Read>(reader: &mut R) -> Result<(Vec<u8>, Vec<u32>)
     Ok((buf, chunk_byte_indices))
 }
 
+/// Appends a deserialized chunk segment to existing accumulated buffers.
+///
+/// `deserialize_chunks` returns `chunk_byte_indices` starting with a leading `0`.
+/// When concatenating multiple segments, this function deduplicates that leading
+/// zero for subsequent segments and rebases all indices to account for data already
+/// accumulated.
+pub fn append_chunk_segment(
+    all_data: &mut Vec<u8>,
+    all_chunk_indices: &mut Vec<u32>,
+    segment_data: &[u8],
+    segment_indices: &[u32],
+) {
+    let base_offset = all_data.len() as u32;
+    if all_chunk_indices.is_empty() {
+        all_chunk_indices.extend_from_slice(segment_indices);
+    } else {
+        all_chunk_indices.extend(segment_indices.iter().skip(1).map(|&o| o + base_offset));
+    }
+    all_data.extend_from_slice(segment_data);
+}
+
 /// Reads the next chunk header, returning `None` on clean EOF.
 ///
 /// Uses a single `read()` call to detect EOF (returns 0), then completes
@@ -338,6 +359,37 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_append_chunk_segment() {
+        let mut all_data = Vec::new();
+        let mut all_indices = Vec::<u32>::new();
+
+        // First segment: simulates deserialize_chunks output [0, 10, 25]
+        append_chunk_segment(&mut all_data, &mut all_indices, &[0u8; 25], &[0, 10, 25]);
+        assert_eq!(all_data.len(), 25);
+        assert_eq!(all_indices, vec![0, 10, 25]);
+
+        // Second segment: [0, 8, 20] — leading 0 should be skipped, offsets rebased by 25
+        append_chunk_segment(&mut all_data, &mut all_indices, &[1u8; 20], &[0, 8, 20]);
+        assert_eq!(all_data.len(), 45);
+        assert_eq!(all_indices, vec![0, 10, 25, 33, 45]);
+
+        // Third segment: single chunk [0, 5] — leading 0 skipped, rebased by 45
+        append_chunk_segment(&mut all_data, &mut all_indices, &[2u8; 5], &[0, 5]);
+        assert_eq!(all_data.len(), 50);
+        assert_eq!(all_indices, vec![0, 10, 25, 33, 45, 50]);
+    }
+
+    #[test]
+    fn test_append_chunk_segment_single() {
+        let mut all_data = Vec::new();
+        let mut all_indices = Vec::<u32>::new();
+
+        append_chunk_segment(&mut all_data, &mut all_indices, &[0u8; 10], &[0, 10]);
+        assert_eq!(all_data.len(), 10);
+        assert_eq!(all_indices, vec![0, 10]);
+    }
+
     #[test]
     fn test_truncated_stream_returns_error() {
         let (_, xorb_data, _, _) = build_xorb_object(3, ChunkSize::Fixed(1024), CompressionScheme::None);

xet_data/src/file_reconstruction/file_reconstructor.rs

@@ -375,6 +375,7 @@ mod tests {
     use ulid::Ulid;
     use xet_client::cas_client::{ClientTestingUtils, DirectAccessClient, LocalClient, RandomFileContents};
     use xet_client::cas_types::FileRange;
+    use xet_runtime::core::XetRuntime;
 
     use super::*;
     use crate::progress_tracking::NoOpProgressUpdater;
@@ -405,6 +406,7 @@ mod tests {
         file_hash: MerkleHash,
         byte_range: Option<FileRange>,
         config: &ReconstructionConfig,
+        semaphore: Option<Arc<AdjustableSemaphore>>,
     ) -> Result<Vec<u8>> {
         let buffer = Arc::new(std::sync::Mutex::new(Cursor::new(Vec::new())));
         let writer = StaticCursorWriter(buffer.clone());
@@ -415,6 +417,9 @@ mod tests {
         if let Some(range) = byte_range {
             reconstructor = reconstructor.with_byte_range(range);
         }
+        if let Some(sem) = semaphore {
+            reconstructor = reconstructor.with_buffer_semaphore(sem);
+        }
 
         reconstructor.reconstruct_to_writer(writer).await?;
 
@@ -528,7 +533,7 @@ mod tests {
             config.use_vectored_write = use_vectored;
 
             // Test 1: reconstruct_to_writer
-            let vec_result = reconstruct_to_vec(client, h, None, &config).await.unwrap();
+            let vec_result = reconstruct_to_vec(client, h, None, &config, None).await.unwrap();
             assert_eq!(vec_result, *expected, "vec failed (vectored={use_vectored})");
 
             // Test 2: reconstruct_to_file
@@ -560,7 +565,7 @@ mod tests {
             config.use_vectored_write = use_vectored;
 
             // Test 1: reconstruct_to_writer
-            let vec_result = reconstruct_to_vec(client, file_contents.file_hash, Some(range), &config)
+            let vec_result = reconstruct_to_vec(client, file_contents.file_hash, Some(range), &config, None)
                 .await
                 .expect("reconstruct_to_vec should succeed");
             assert_eq!(vec_result, expected, "vec failed (vectored={use_vectored})");
@@ -911,7 +916,11 @@ mod tests {
     #[tokio::test]
     async fn test_non_contiguous_chunks() {
         let (client, file_contents) = setup_test_file(&[(1, (0, 2)), (1, (4, 6))]).await;
-        reconstruct_and_verify_full(&client, &file_contents, test_config()).await;
+        let config = test_config();
+        let result = reconstruct_to_vec(&client, file_contents.file_hash, None, &config, None)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data);
     }
 
     // ==================== Default Config Tests ====================
@@ -1157,7 +1166,7 @@ mod tests {
             let mut config = test_config();
             config.download_buffer_perfile_size = xet_runtime::utils::ByteSize::from("8kb");
 
-            let reconstructed = reconstruct_to_vec(&client, file_contents.file_hash, None, &config)
+            let reconstructed = reconstruct_to_vec(&client, file_contents.file_hash, None, &config, None)
                 .await
                 .unwrap();
             assert_eq!(reconstructed, file_contents.data);
@@ -1287,6 +1296,348 @@ mod tests {
         assert_eq!(&result[start as usize..end as usize], &file_contents.data[start as usize..end as usize]);
     }
 
+    // ==================== V1 Fallback Tests ====================
+    //
+    // These tests use LocalTestServer with V2 disabled to verify that
+    // reconstruction works correctly when the client falls back from V2 to V1.
+
+    /// Helper to reconstruct through a LocalTestServer (RemoteClient HTTP path).
+    async fn reconstruct_via_server(
+        server: &xet_client::cas_client::LocalTestServer,
+        file_hash: MerkleHash,
+        byte_range: Option<FileRange>,
+        config: &ReconstructionConfig,
+    ) -> Result<Vec<u8>> {
+        let buffer = Arc::new(std::sync::Mutex::new(Cursor::new(Vec::new())));
+        let writer = StaticCursorWriter(buffer.clone());
+
+        let client: Arc<dyn Client> = server.remote_client().clone();
+        let mut reconstructor = FileReconstructor::new(&client, file_hash).with_config(config);
+
+        if let Some(range) = byte_range {
+            reconstructor = reconstructor.with_byte_range(range);
+        }
+
+        reconstructor.reconstruct_to_writer(writer).await?;
+
+        let data = buffer.lock().unwrap().get_ref().clone();
+        Ok(data)
+    }
+
+    #[tokio::test]
+    async fn test_v1_fallback_full_reconstruction() {
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(&[(1, (0, 3)), (2, (0, 2))], TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        // Disable V2 so the remote client falls back to V1 + conversion.
+        server.disable_v2_reconstruction(404);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, None, &config)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    #[tokio::test]
+    async fn test_v1_fallback_partial_range() {
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(&[(1, (0, 5)), (2, (0, 3))], TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        server.disable_v2_reconstruction(404);
+
+        let file_len = file_contents.data.len() as u64;
+        let range = FileRange::new(file_len / 4, file_len * 3 / 4);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, Some(range), &config)
+            .await
+            .unwrap();
+        assert_eq!(result, &file_contents.data[range.start as usize..range.end as usize]);
+    }
+
+    #[tokio::test]
+    async fn test_v1_fallback_non_contiguous_chunks() {
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(&[(1, (0, 2)), (1, (4, 6))], TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        server.disable_v2_reconstruction(404);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, None, &config)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    #[tokio::test]
+    async fn test_v1_fallback_multiple_xorbs() {
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(&[(1, (0, 2)), (2, (0, 3)), (3, (0, 2)), (1, (2, 4))], TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        server.disable_v2_reconstruction(404);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, None, &config)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    /// V1 fallback with three disjoint ranges from the same xorb.
+    #[tokio::test]
+    async fn test_v1_fallback_triple_disjoint_ranges() {
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))], TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        server.disable_v2_reconstruction(404);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, None, &config)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    // ==================== Max Ranges Tests ====================
+    //
+    // These tests use LocalTestServer with max_ranges_per_fetch=2 to verify that
+    // multi-range fetch splitting works correctly through the full HTTP path.
+
+    /// Helper to set up a server with max_ranges_per_fetch and reconstruct.
+    async fn reconstruct_via_server_with_max_ranges(
+        term_spec: &[(u64, (u64, u64))],
+        max_ranges: usize,
+        byte_range: Option<FileRange>,
+    ) -> (Vec<u8>, RandomFileContents) {
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(term_spec, TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        server.set_max_ranges_per_fetch(max_ranges);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, byte_range, &config)
+            .await
+            .unwrap();
+        (result, file_contents)
+    }
+
+    #[tokio::test]
+    async fn test_max_ranges_simple() {
+        let (result, file_contents) =
+            reconstruct_via_server_with_max_ranges(&[(1, (0, 3)), (2, (0, 2))], 2, None).await;
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    /// A single xorb with two disjoint ranges, split at max_ranges=1.
+    /// Each range becomes its own fetch entry.
+    #[tokio::test]
+    async fn test_max_ranges_1_disjoint() {
+        let (result, file_contents) =
+            reconstruct_via_server_with_max_ranges(&[(1, (0, 2)), (1, (4, 6))], 1, None).await;
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    /// Three disjoint ranges from the same xorb with max_ranges=2.
+    /// First two ranges are grouped, third gets its own fetch entry.
+    #[tokio::test]
+    async fn test_max_ranges_2_triple_disjoint() {
+        let (result, file_contents) =
+            reconstruct_via_server_with_max_ranges(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))], 2, None).await;
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    /// Multiple xorbs, each with disjoint ranges, with max_ranges=2.
+    /// Tests that splitting is applied per-xorb correctly.
+    #[tokio::test]
+    async fn test_max_ranges_2_multi_xorb_disjoint() {
+        let term_spec = &[
+            (1, (0, 2)),
+            (2, (0, 2)),
+            (1, (4, 6)),
+            (2, (4, 6)),
+            (1, (8, 10)),
+            (2, (8, 10)),
+        ];
+        let (result, file_contents) = reconstruct_via_server_with_max_ranges(term_spec, 2, None).await;
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    /// Complex interleaved pattern with max_ranges=2 and a partial byte range.
+    #[tokio::test]
+    async fn test_max_ranges_2_partial_range() {
+        let term_spec = &[
+            (1, (0, 3)),
+            (2, (0, 2)),
+            (1, (3, 5)),
+            (3, (1, 4)),
+            (2, (4, 6)),
+            (1, (0, 2)),
+        ];
+        let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+        let file_contents = server
+            .remote_client()
+            .upload_random_file(term_spec, TEST_CHUNK_SIZE)
+            .await
+            .unwrap();
+
+        server.set_max_ranges_per_fetch(2);
+
+        let file_len = file_contents.data.len() as u64;
+        let range = FileRange::new(file_len / 4, file_len * 3 / 4);
+
+        let config = test_config();
+        let result = reconstruct_via_server(&server, file_contents.file_hash, Some(range), &config)
+            .await
+            .unwrap();
+        assert_eq!(result, &file_contents.data[range.start as usize..range.end as usize]);
+    }
+
+    // ==================== Multi-Disjoint Range Tests (LocalClient) ====================
+    //
+    // These tests exercise complex disjoint range patterns through the LocalClient path
+    // (no HTTP server), ensuring the reconstruction logic handles V2 multi-range
+    // XorbBlocks correctly.
+
+    /// Single xorb with three disjoint chunk ranges.
+    #[tokio::test]
+    async fn test_triple_disjoint_ranges_full() {
+        let (client, file_contents) = setup_test_file(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))]).await;
+        reconstruct_and_verify_full(&client, &file_contents, test_config()).await;
+    }
+
+    /// Single xorb with three disjoint chunk ranges, partial byte range.
+    #[tokio::test]
+    async fn test_triple_disjoint_ranges_partial() {
+        let (client, file_contents) = setup_test_file(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))]).await;
+        let file_len = file_contents.data.len() as u64;
+        let range = FileRange::new(file_len / 4, file_len * 3 / 4);
+        reconstruct_and_verify_range(&client, &file_contents, range, test_config()).await;
+    }
+
+    /// Multiple xorbs, each with multiple disjoint ranges, interleaved.
+    #[tokio::test]
+    async fn test_multi_xorb_interleaved_disjoint() {
+        let term_spec = &[
+            (1, (0, 2)),
+            (2, (0, 2)),
+            (1, (4, 6)),
+            (2, (4, 6)),
+            (1, (8, 10)),
+            (2, (8, 10)),
+        ];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        reconstruct_and_verify_full(&client, &file_contents, test_config()).await;
+    }
+
+    /// Multiple xorbs with interleaved disjoint ranges, partial byte range.
+    #[tokio::test]
+    async fn test_multi_xorb_interleaved_disjoint_partial() {
+        let term_spec = &[
+            (1, (0, 2)),
+            (2, (0, 2)),
+            (1, (4, 6)),
+            (2, (4, 6)),
+            (1, (8, 10)),
+            (2, (8, 10)),
+        ];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        let file_len = file_contents.data.len() as u64;
+        let range = FileRange::new(file_len / 3, file_len * 2 / 3);
+        reconstruct_and_verify_range(&client, &file_contents, range, test_config()).await;
+    }
+
+    /// Single xorb with four disjoint ranges (many gaps).
+    #[tokio::test]
+    async fn test_four_disjoint_ranges() {
+        let term_spec = &[(1, (0, 2)), (1, (4, 6)), (1, (8, 10)), (1, (12, 14))];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        reconstruct_and_verify_full(&client, &file_contents, test_config()).await;
+    }
+
+    /// Mix of contiguous and disjoint ranges from the same xorb.
+    #[tokio::test]
+    async fn test_mixed_contiguous_and_disjoint() {
+        let term_spec = &[
+            (1, (0, 3)),  // contiguous block
+            (1, (3, 5)),  // continues contiguously
+            (1, (8, 10)), // gap, then disjoint
+        ];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        reconstruct_and_verify_full(&client, &file_contents, test_config()).await;
+    }
+
+    /// Disjoint ranges across three xorbs with a complex access pattern.
+    #[tokio::test]
+    async fn test_complex_three_xorb_disjoint() {
+        let term_spec = &[
+            (1, (0, 2)),
+            (2, (0, 3)),
+            (3, (2, 5)),
+            (1, (5, 8)),
+            (2, (6, 8)),
+            (3, (0, 2)),
+        ];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        reconstruct_and_verify_full(&client, &file_contents, test_config()).await;
+    }
+
+    /// LocalClient with max_ranges_per_fetch=2 (tests V2 response splitting without HTTP).
+    #[tokio::test]
+    async fn test_local_client_max_ranges_2_disjoint() {
+        let client = LocalClient::temporary().await.unwrap();
+        client.set_max_ranges_per_fetch(2);
+
+        let term_spec = &[(1, (0, 2)), (1, (4, 6)), (1, (8, 10)), (1, (12, 14))];
+        let file_contents = client.upload_random_file(term_spec, TEST_CHUNK_SIZE).await.unwrap();
+
+        let config = test_config();
+        let result = reconstruct_to_vec(&client, file_contents.file_hash, None, &config, None)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
+    /// LocalClient with max_ranges_per_fetch=1 (every range gets its own fetch entry).
+    #[tokio::test]
+    async fn test_local_client_max_ranges_1_multi_xorb() {
+        let client = LocalClient::temporary().await.unwrap();
+        client.set_max_ranges_per_fetch(1);
+
+        let term_spec = &[(1, (0, 2)), (2, (0, 2)), (1, (4, 6)), (2, (4, 6))];
+        let file_contents = client.upload_random_file(term_spec, TEST_CHUNK_SIZE).await.unwrap();
+
+        let config = test_config();
+        let result = reconstruct_to_vec(&client, file_contents.file_hash, None, &config, None)
+            .await
+            .unwrap();
+        assert_eq!(result, file_contents.data.as_ref());
+    }
+
     // ==================== Cancellation Flag Tests ====================
 
     #[tokio::test]
@@ -1385,4 +1736,132 @@ mod tests {
         assert_eq!(bytes_written, file_contents.data.len() as u64);
         assert_eq!(buffer.lock().unwrap().get_ref().clone(), file_contents.data);
     }
+
+    // ==================== Multirange Fetching Tests ====================
+    //
+    // These tests verify that reconstruction works correctly with both values
+    // of `enable_multirange_fetching`. When true, V2 multi-range fetch entries
+    // are used as-is (multirange HTTP requests). When false (default), each
+    // range is split into its own XorbBlock and fetched via a separate
+    // single-range request in parallel.
+    //
+    // Uses XetRuntime::new_with_config() to override the config per-test,
+    // following the pattern from test_dynamic_buffer_scaling_noop_increment_preserves_total_permits.
+
+    fn with_multirange_config(enable: bool) -> Arc<XetRuntime> {
+        let mut config = xet_runtime::config::XetConfig::new();
+        config.client.enable_multirange_fetching = enable;
+        XetRuntime::new_with_config(config).unwrap()
+    }
+
+    /// Exercises multiple disjoint-range scenarios through LocalClient with both
+    /// enable_multirange_fetching=true and =false.
+    #[test]
+    fn test_multirange_local_client() {
+        for enable in [false, true] {
+            let rt = with_multirange_config(enable);
+            rt.external_run_async_task(async move {
+                let scenarios: Vec<Vec<(u64, (u64, u64))>> = vec![
+                    vec![(1, (0, 2)), (1, (4, 6)), (1, (8, 10))],
+                    vec![
+                        (1, (0, 2)),
+                        (2, (0, 2)),
+                        (1, (4, 6)),
+                        (2, (4, 6)),
+                        (1, (8, 10)),
+                        (2, (8, 10)),
+                    ],
+                    vec![
+                        (1, (0, 2)),
+                        (2, (0, 3)),
+                        (3, (2, 5)),
+                        (1, (5, 8)),
+                        (2, (6, 8)),
+                        (3, (0, 2)),
+                    ],
+                ];
+                let config = test_config();
+                for term_spec in &scenarios {
+                    let (client, fc) = setup_test_file(term_spec).await;
+                    reconstruct_and_verify_full(&client, &fc, config.clone()).await;
+
+                    let file_len = fc.data.len() as u64;
+                    let range = FileRange::new(file_len / 4, file_len * 3 / 4);
+                    reconstruct_and_verify_range(&client, &fc, range, config.clone()).await;
+                }
+            })
+            .unwrap();
+        }
+    }
+
+    /// LocalClient with max_ranges_per_fetch constraint, both enable settings.
+    #[test]
+    fn test_multirange_max_ranges() {
+        for enable in [false, true] {
+            let rt = with_multirange_config(enable);
+            rt.external_run_async_task(async {
+                let client = LocalClient::temporary().await.unwrap();
+                client.set_max_ranges_per_fetch(2);
+
+                let term_spec = &[(1, (0, 2)), (1, (4, 6)), (1, (8, 10)), (1, (12, 14))];
+                let fc = client.upload_random_file(term_spec, TEST_CHUNK_SIZE).await.unwrap();
+
+                let config = test_config();
+                let result = reconstruct_to_vec(&client, fc.file_hash, None, &config, None).await.unwrap();
+                assert_eq!(result, fc.data.as_ref());
+            })
+            .unwrap();
+        }
+    }
+
+    /// Exercises HTTP server path with full, max-ranges-split, and partial-range
+    /// reconstruction, both enable_multirange_fetching values.
+    #[test]
+    fn test_multirange_via_server() {
+        for enable in [false, true] {
+            let rt = with_multirange_config(enable);
+            rt.external_run_async_task(async {
+                let config = test_config();
+
+                // Full reconstruction with disjoint ranges
+                let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+                let fc = server
+                    .remote_client()
+                    .upload_random_file(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))], TEST_CHUNK_SIZE)
+                    .await
+                    .unwrap();
+                let result = reconstruct_via_server(&server, fc.file_hash, None, &config).await.unwrap();
+                assert_eq!(result, fc.data.as_ref());
+
+                // Multi-xorb with max_ranges_per_fetch=2
+                let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+                let fc = server
+                    .remote_client()
+                    .upload_random_file(
+                        &[(1, (0, 2)), (2, (0, 2)), (1, (4, 6)), (2, (4, 6)), (1, (8, 10))],
+                        TEST_CHUNK_SIZE,
+                    )
+                    .await
+                    .unwrap();
+                server.set_max_ranges_per_fetch(2);
+                let result = reconstruct_via_server(&server, fc.file_hash, None, &config).await.unwrap();
+                assert_eq!(result, fc.data.as_ref());
+
+                // Partial byte range
+                let server = xet_client::cas_client::LocalTestServerBuilder::new().start().await;
+                let fc = server
+                    .remote_client()
+                    .upload_random_file(&[(1, (0, 3)), (2, (0, 2)), (1, (3, 5)), (2, (4, 6))], TEST_CHUNK_SIZE)
+                    .await
+                    .unwrap();
+                let file_len = fc.data.len() as u64;
+                let range = FileRange::new(file_len / 4, file_len * 3 / 4);
+                let result = reconstruct_via_server(&server, fc.file_hash, Some(range), &config)
+                    .await
+                    .unwrap();
+                assert_eq!(result, &fc.data[range.start as usize..range.end as usize]);
+            })
+            .unwrap();
+        }
+    }
 }

xet_data/src/file_reconstruction/reconstruction_terms/file_term.rs

@@ -7,6 +7,7 @@ use tokio::sync::OnceCell;
 use xet_client::cas_client::Client;
 use xet_client::cas_types::{ChunkRange, FileRange, HttpRange};
 use xet_core_structures::merklehash::MerkleHash;
+use xet_runtime::core::xet_config;
 use xet_runtime::utils::UniqueId;
 
 use super::super::FileReconstructionError;
@@ -19,17 +20,28 @@ use crate::progress_tracking::download_tracking::DownloadTaskUpdater;
 /// in the output file that maps to a chunk range within a xorb block.
 #[derive(Clone)]
 pub struct FileTerm {
+    // The byte range in the file of this term.
     pub byte_range: FileRange,
+
+    // Absolute chunk range within the full xorb.  Doesn't account for only a partial xorb being downloaded.
     pub xorb_chunk_range: ChunkRange,
+
+    // The index of the (chunk index, byte offset) pair in the xorb block that starts this file term.
+    pub xorb_block_start_index: usize,
+
+    // The byte offset into the first range of the xorb block should this term not start on a chunk boundary.
     pub offset_into_first_range: u64,
+
+    // The xorb block that sourced this file term.
     pub xorb_block: Arc<XorbBlock>,
+
+    // The retrieval URL information for this file term.
     pub url_info: Arc<TermBlockRetrievalURLs>,
 }
 
 impl FileTerm {
     pub fn extract_bytes(&self, xorb_block_data: &XorbBlockData) -> Bytes {
-        let local_start_chunk = (self.xorb_chunk_range.start - self.xorb_block.chunk_range.start) as usize;
-        let start_byte_offset = xorb_block_data.chunk_offsets[local_start_chunk];
+        let (_, start_byte_offset) = xorb_block_data.chunk_offsets[self.xorb_block_start_index];
         let start_byte_offset = start_byte_offset + self.offset_into_first_range as usize;
         let expected_size = (self.byte_range.end - self.byte_range.start) as usize;
         let end_byte_offset = start_byte_offset + expected_size;
@@ -67,6 +79,25 @@ impl FileTerm {
     }
 }
 
+/// Intermediate data for a single file term, collected during the first pass of
+/// `retrieve_file_term_block` before the final `FileTerm` structs are built.
+///
+/// We need this because `FileTerm` requires `Arc<XorbBlock>` and `Arc<TermBlockRetrievalURLs>`,
+/// which can't be constructed until all terms have been processed.
+struct FileTermEntry {
+    /// The byte range in the output file that this term covers.
+    byte_range: FileRange,
+    /// The chunk range within the xorb that sources this term's data.
+    xorb_chunk_range: ChunkRange,
+    /// Byte offset into the first chunk's data, non-zero only for the first term
+    /// when the query range starts mid-chunk.
+    offset_into_first_range: u64,
+    /// Index into the `xorb_blocks` / `xorb_block_retrieval_urls` vectors.
+    xorb_block_index: usize,
+    /// Flattened index into the xorb block's `chunk_offsets` for this term's start chunk.
+    xorb_block_start_index: usize,
+}
+
 /// Retrieve file terms from the client for a given file hash and byte range.
 /// Returns None if the requested byte range is past the end of the file.
 /// Returns the actual retrieved range and the number of bytes required for the
@@ -77,78 +108,111 @@ pub async fn retrieve_file_term_block(
     file_hash: MerkleHash,
     query_file_byte_range: FileRange,
 ) -> Result<Option<(FileRange, u64, Vec<FileTerm>)>> {
-    // First, get the raw reconstruction.
+    // get_reconstruction always returns V2 format (the client converts V1 internally).
     let Some(raw_reconstruction) = client.get_reconstruction(&file_hash, Some(query_file_byte_range)).await? else {
         // None means we've requested a byte range beyond the end of the file.
         return Ok(None);
     };
 
-    // Set a new url acquisition id to ensure that we don't double up the url acquisitions.
+    // Each acquisition gets a unique ID used for single-flight URL refresh dedup.
     let acquisition_id = UniqueId::new();
 
-    // Intermediate storage for file term data before we create the actual FileTerm structs.
-    // (byte_range, xorb_chunk_range, offset_into_first_range, index into xorb_blocks)
-    let mut file_term_data = Vec::<(FileRange, ChunkRange, u64, usize)>::with_capacity(raw_reconstruction.terms.len());
+    // First pass: iterate through the reconstruction terms and build up intermediate
+    // FileTermEntry data, XorbBlock objects, and retrieval URL info.  We can't construct
+    // the final FileTerm structs yet because they need Arc<XorbBlock> and Arc<TermBlockRetrievalURLs>,
+    // which require all terms to be processed first.
+    let mut file_term_data = Vec::<FileTermEntry>::with_capacity(raw_reconstruction.terms.len());
 
-    let n_xorb_terms = raw_reconstruction.fetch_info.values().map(|v| v.len()).sum();
+    // Parallel vectors indexed by xorb_block_index:
+    // - xorb_blocks: the block metadata (hash, chunk ranges, references)
+    // - xorb_block_retrieval_urls: the download URL and byte ranges for each block
+    let mut xorb_blocks: Vec<XorbBlock> = Vec::new();
+    let mut xorb_block_retrieval_urls = Vec::<(String, Vec<HttpRange>)>::new();
 
-    // Keep track of the xorb blocks we've created, keyed by (xorb_hash, first chunk index).
-    let mut xorb_blocks: Vec<XorbBlock> = Vec::with_capacity(n_xorb_terms);
+    // Dedup map: (xorb_hash, first_range_chunk_start) -> xorb_block_index.
+    // Multiple terms may reference the same xorb block; this ensures we create
+    // each block only once and share it across terms.
+    let mut xorb_index_lookup = HashMap::<(MerkleHash, u32), usize>::new();
 
-    // Keep track of the URLs for each.
-    let mut xorb_block_retrieval_urls = Vec::<(String, HttpRange)>::with_capacity(n_xorb_terms);
-
-    // Get a hash map so we can reindex the xorb terms; map of (xorb_hash, first chunk index) -> xorb block index.
-    let mut xorb_index_lookup = HashMap::<(MerkleHash, u64), usize>::with_capacity(n_xorb_terms);
-
-    // Keep track of where we are so as to map the file terms to the byte range within the file.
+    // Track the current byte offset in the output file as we process terms sequentially.
     let mut cur_file_byte_offset = query_file_byte_range.start;
 
-    // We'll create the URL info after processing all terms, once we know the actual range.
+    let enable_multirange = xet_config().client.enable_multirange_fetching;
 
-    // Iterate over the terms and build the file terms and xorb terms.
     for (local_term_index, term) in raw_reconstruction.terms.iter().enumerate() {
         let xorb_hash: MerkleHash = term.hash.into();
 
-        // Get the xorb info here.
-        let Some(xorb_info) = raw_reconstruction.fetch_info.get(&term.hash) else {
+        let Some(xorb_descriptor) = raw_reconstruction.xorbs.get(&term.hash) else {
             return Err(FileReconstructionError::CorruptedReconstruction(format!(
                 "Xorb info not found for xorb hash {xorb_hash:?}"
             )));
         };
 
-        // Get the xorb block index that this term belongs to.
+        // Find the XorbBlock for this term's chunk range. The behavior depends on the
+        // enable_multirange_fetching config:
+        //
+        // - When true: one XorbBlock per XorbMultiRangeFetch entry, preserving all ranges in a single block
+        //   (multi-range HTTP request).
+        // - When false (default): one XorbBlock per individual XorbRangeDescriptor, so each range is fetched as a
+        //   separate single-range HTTP request in parallel.
         let xorb_block_index = 'find_xorb_block: {
-            for raw_xorb_block_info in xorb_info.iter() {
-                let chunk_range = raw_xorb_block_info.range;
+            for fetch_entry in xorb_descriptor.iter() {
+                if enable_multirange {
+                    let term_contained = fetch_entry
+                        .ranges
+                        .iter()
+                        .any(|r| r.chunks.start <= term.range.start && term.range.end <= r.chunks.end);
 
-                if chunk_range.start <= term.range.start && term.range.start <= chunk_range.end {
-                    // Verify that the term range is contained within the xorb block.
-                    if term.range.end > chunk_range.end {
-                        return Err(FileReconstructionError::CorruptedReconstruction(format!(
-                            "Term range extends beyond xorb block range for xorb hash {xorb_hash:?}"
-                        )));
+                    if !term_contained {
+                        continue;
                     }
 
-                    // Reuse the previous one if it exists, otherwise insert a new one.
-                    let index = match xorb_index_lookup.entry((xorb_hash, chunk_range.start as u64)) {
+                    let first_chunk_start = fetch_entry.ranges[0].chunks.start;
+
+                    let index = match xorb_index_lookup.entry((xorb_hash, first_chunk_start)) {
                         Entry::Occupied(entry) => *entry.get(),
                         Entry::Vacant(entry) => {
                             let new_index = xorb_blocks.len();
+
+                            let chunk_ranges: Vec<ChunkRange> = fetch_entry.ranges.iter().map(|r| r.chunks).collect();
+                            let http_ranges: Vec<HttpRange> = fetch_entry.ranges.iter().map(|r| r.bytes).collect();
+
                             xorb_blocks.push(XorbBlock {
                                 xorb_hash,
-                                chunk_range,
+                                chunk_ranges,
                                 xorb_block_index: new_index,
                                 references: vec![],
                                 uncompressed_size_if_known: None,
                                 data: OnceCell::new(),
                             });
 
-                            // Store the retrieval URL and range for this xorb block.
-                            xorb_block_retrieval_urls
-                                .push((raw_xorb_block_info.url.clone(), raw_xorb_block_info.url_range));
+                            xorb_block_retrieval_urls.push((fetch_entry.url.clone(), http_ranges));
+
+                            entry.insert(new_index);
+                            new_index
+                        },
+                    };
+
+                    break 'find_xorb_block index;
+                } else {
+                    for range in &fetch_entry.ranges {
+                        if range.chunks.start <= term.range.start && term.range.end <= range.chunks.end {
+                            let index = match xorb_index_lookup.entry((xorb_hash, range.chunks.start)) {
+                                Entry::Occupied(entry) => *entry.get(),
+                                Entry::Vacant(entry) => {
+                                    let new_index = xorb_blocks.len();
+
+                                    xorb_blocks.push(XorbBlock {
+                                        xorb_hash,
+                                        chunk_ranges: vec![range.chunks],
+                                        xorb_block_index: new_index,
+                                        references: vec![],
+                                        uncompressed_size_if_known: None,
+                                        data: OnceCell::new(),
+                                    });
+
+                                    xorb_block_retrieval_urls.push((fetch_entry.url.clone(), vec![range.bytes]));
 
-                            // Store the index.
                                     entry.insert(new_index);
                                     new_index
                                 },
@@ -157,90 +221,120 @@ pub async fn retrieve_file_term_block(
                             break 'find_xorb_block index;
                         }
                     }
+                }
+            }
             return Err(FileReconstructionError::CorruptedReconstruction(format!(
-                "No xorb chunk range found for file term {local_term_index:?} in xorb info for xorb hash {xorb_hash:?}"
+                "No xorb fetch entry found for file term {local_term_index:?} in xorb info for xorb hash {xorb_hash:?}"
             )));
         };
 
-        // Do we need to adjust for an offset into the first range?
-        let offset_into_first_range = {
-            if local_term_index == 0 {
+        // Only the first term can have a non-zero offset into its first chunk,
+        // which happens when the query byte range starts mid-chunk.
+        let offset_into_first_range = if local_term_index == 0 {
             raw_reconstruction.offset_into_first_range
         } else {
             0
-            }
         };
 
-        // The effective size of this term in the file.
+        // The term's contribution to the output file is its full uncompressed size
+        // minus any offset into the first chunk.
         let term_byte_size = term.unpacked_length as u64 - offset_into_first_range;
 
-        // Update the references term on the XorbBlock to track where the xorb gets used.
+        // Record this term as a reference on its xorb block (used later to determine
+        // whether the block's total uncompressed size can be inferred).
         xorb_blocks[xorb_block_index].references.push(XorbReference {
             term_chunks: term.range,
             uncompressed_size: term.unpacked_length as usize,
         });
 
-        // Store the file term data (byte_range, xorb_chunk_range, offset_into_first_range, xorb_block_index).
-        // We'll create the FileTerm structs after we know the actual range.
-        file_term_data.push((
-            FileRange::new(cur_file_byte_offset, cur_file_byte_offset + term_byte_size),
-            term.range,
+        // Compute the flattened index into the block's chunk_offsets for this term's
+        // starting chunk. This accounts for disjoint chunk ranges in multi-range blocks.
+        //
+        // The term_contained check above guarantees term.range.start falls within one of
+        // the block's chunk_ranges, so this loop always finds a match.
+        let xorb_block_start_index = {
+            let chunk_start = term.range.start;
+            let chunk_ranges = &xorb_blocks[xorb_block_index].chunk_ranges;
+            let mut idx = 0;
+            let mut found = false;
+            for range in chunk_ranges {
+                if chunk_start >= range.start && chunk_start < range.end {
+                    idx += (chunk_start - range.start) as usize;
+                    found = true;
+                    break;
+                }
+                idx += (range.end - range.start) as usize;
+            }
+            if !found {
+                return Err(FileReconstructionError::CorruptedReconstruction(format!(
+                    "chunk_start {chunk_start} not found in chunk_ranges {chunk_ranges:?} for file term {local_term_index}"
+                )));
+            }
+            idx
+        };
+
+        file_term_data.push(FileTermEntry {
+            byte_range: FileRange::new(cur_file_byte_offset, cur_file_byte_offset + term_byte_size),
+            xorb_chunk_range: term.range,
             offset_into_first_range,
             xorb_block_index,
-        ));
+            xorb_block_start_index,
+        });
 
         cur_file_byte_offset += term_byte_size;
     }
 
-    // Sort the block references so that we can easily scan the terms to figure out how many references
-    // a particular chunk may have.
+    // Sort each block's references by chunk start so that determine_size_if_possible
+    // can use its forward-chaining DP to check coverage.
     for block in &mut xorb_blocks {
         block.references.sort_by_key(|r| r.term_chunks.start);
-        block.uncompressed_size_if_known = XorbBlock::determine_size_if_possible(block.chunk_range, &block.references);
+        block.uncompressed_size_if_known =
+            XorbBlock::determine_size_if_possible(&block.chunk_ranges, &block.references);
     }
 
-    // Now, it's possible that we have to shrink the byte range of the last term, as we may have retrieved more
-    // due to chunk offsets.
+    // The last term in the reconstruction may extend beyond the requested range
+    // (e.g. when the query ends mid-chunk). Trim it to the query boundary.
     if cur_file_byte_offset > query_file_byte_range.end {
         let last_term_shrinkage = cur_file_byte_offset - query_file_byte_range.end;
 
         debug_assert!(!file_term_data.is_empty());
 
-        if let Some(fi) = file_term_data.last_mut() {
-            fi.0.end -= last_term_shrinkage;
+        if let Some(entry) = file_term_data.last_mut() {
+            entry.byte_range.end -= last_term_shrinkage;
         }
     }
 
-    // Calculate the actual retrieved range from the file terms.
+    // The actual range covered, which may be smaller than requested if the file
+    // ends before the requested range.
     let actual_range = FileRange::new(
-        file_term_data.first().map(|(br, _, _, _)| br.start).unwrap_or(0),
-        file_term_data.last().map(|(br, _, _, _)| br.end).unwrap_or(0),
+        file_term_data.first().map(|e| e.byte_range.start).unwrap_or(0),
+        file_term_data.last().map(|e| e.byte_range.end).unwrap_or(0),
     );
 
-    // Now, calculate the total number of bytes that needs to be downloaded given dedup and compression savings.
-    let total_transfer_bytes = xorb_block_retrieval_urls
+    // Total compressed bytes that will be transferred across all xorb block downloads.
+    let total_transfer_bytes: u64 = xorb_block_retrieval_urls
         .iter()
-        .map(|(_, http_range)| {
-            let file_range = FileRange::from(*http_range);
-            file_range.end.saturating_sub(file_range.start)
-        })
+        .flat_map(|(_, ranges)| ranges)
+        .map(|r| r.length())
         .sum();
 
-    // Now create the URL info with the actual range and retrieval URLs.
+    // Wrap the retrieval URLs in a shared struct so all file terms can share them
+    // and coordinate URL refreshes through a single lock.
     let url_info =
         Arc::new(TermBlockRetrievalURLs::new(file_hash, actual_range, acquisition_id, xorb_block_retrieval_urls));
 
-    // Convert xorb_blocks to Arc<XorbBlock> for use in FileTerms.
+    // Second pass: convert the intermediate FileTermEntry data into final FileTerm
+    // structs, now that we can wrap xorb blocks in Arc and share the url_info.
     let xorb_blocks_arc: Vec<Arc<XorbBlock>> = xorb_blocks.into_iter().map(Arc::new).collect();
 
-    // Convert the intermediate data to FileTerm structs with the shared url_info.
     let file_terms: Vec<FileTerm> = file_term_data
         .into_iter()
-        .map(|(byte_range, xorb_chunk_range, offset_into_first_range, xorb_block_index)| FileTerm {
-            byte_range,
-            xorb_chunk_range,
-            offset_into_first_range,
-            xorb_block: xorb_blocks_arc[xorb_block_index].clone(),
+        .map(|entry| FileTerm {
+            byte_range: entry.byte_range,
+            xorb_chunk_range: entry.xorb_chunk_range,
+            xorb_block_start_index: entry.xorb_block_start_index,
+            offset_into_first_range: entry.offset_into_first_range,
+            xorb_block: xorb_blocks_arc[entry.xorb_block_index].clone(),
             url_info: url_info.clone(),
         })
         .collect();
@@ -252,7 +346,7 @@ pub async fn retrieve_file_term_block(
 mod tests {
     use std::sync::Arc;
 
-    use more_asserts::{assert_ge, assert_le};
+    use more_asserts::assert_le;
     use xet_client::cas_client::{ClientTestingUtils, LocalClient, RandomFileContents};
     use xet_client::cas_types::{ChunkRange, FileRange};
     use xet_runtime::utils::UniqueId;
@@ -351,10 +445,18 @@ mod tests {
             // Track xorb block index
             seen_xorb_indices.insert(file_term.xorb_block.xorb_block_index);
 
-            // Verify chunk range is within xorb block boundaries.
+            // Verify chunk range is within xorb block boundaries: the term's chunk range
+            // must be contained within at least one of the block's chunk ranges.
             let xorb_block = &file_term.xorb_block;
-            assert_ge!(file_term.xorb_chunk_range.start, xorb_block.chunk_range.start);
-            assert_le!(file_term.xorb_chunk_range.end, xorb_block.chunk_range.end);
+            let term_in_some_range = xorb_block
+                .chunk_ranges
+                .iter()
+                .any(|cr| file_term.xorb_chunk_range.start >= cr.start && file_term.xorb_chunk_range.end <= cr.end);
+            assert!(
+                term_in_some_range,
+                "term chunk range {:?} not within any block chunk range {:?}",
+                file_term.xorb_chunk_range, xorb_block.chunk_ranges
+            );
 
             // Cross-reference with known file contents.
             if expected_term_idx < file_contents.terms.len() {
@@ -365,7 +467,7 @@ mod tests {
 
                 // Verify chunk range matches (accounting for partial first term).
                 if file_term_data_offset == 0 {
-                    assert_eq!(file_term.xorb_chunk_range.start as u32, expected_term.chunk_start);
+                    assert_eq!(file_term.xorb_chunk_range.start, expected_term.chunk_start);
                 }
             }
 
@@ -549,10 +651,11 @@ mod tests {
         // Get the first file term's xorb block to test URL retrieval
         let file_term = &file_terms[0];
         let xorb_block_index = file_term.xorb_block.xorb_block_index;
-        let (unique_id, url, http_range) = file_term.url_info.get_retrieval_url(xorb_block_index).await;
+        let (unique_id, url, http_ranges) = file_term.url_info.get_retrieval_url(xorb_block_index).await;
 
         assert!(!url.is_empty());
-        assert!(http_range.start < http_range.end);
+        assert!(!http_ranges.is_empty());
+        assert!(http_ranges[0].start <= http_ranges[0].end);
         assert!(unique_id != UniqueId::null());
     }
 
@@ -591,87 +694,136 @@ mod tests {
 
     #[tokio::test]
     async fn test_range_few_bytes_before_end() {
-        // Test requesting a range that ends just a few bytes before the file end,
-        // within the same chunk as the file end.
         let (client, file_contents) = setup_test_file(&[(1, (0, 5))]).await;
         let file_len = file_contents.data.len() as u64;
 
-        // Request range ending 3 bytes before the end
         let range = FileRange::new(0, file_len - 3);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
 
-        // Request range ending 1 byte before the end
         let range = FileRange::new(0, file_len - 1);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
     }
 
     #[tokio::test]
     async fn test_range_few_bytes_after_start() {
-        // Test requesting a range that starts just a few bytes after the file start,
-        // within the same chunk as the file start.
         let (client, file_contents) = setup_test_file(&[(1, (0, 5))]).await;
         let file_len = file_contents.data.len() as u64;
 
-        // Request range starting 3 bytes after the start
         let range = FileRange::new(3, file_len);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
 
-        // Request range starting 1 byte after the start
         let range = FileRange::new(1, file_len);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
     }
 
     #[tokio::test]
     async fn test_range_few_bytes_offset_both_ends() {
-        // Test requesting a range with small offsets at both ends within the same chunk.
         let (client, file_contents) = setup_test_file(&[(1, (0, 5))]).await;
         let file_len = file_contents.data.len() as u64;
 
-        // Request range with 2 bytes trimmed from start and 2 bytes from end
         let range = FileRange::new(2, file_len - 2);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
 
-        // Request just the middle byte of a small range
         let range = FileRange::new(file_len / 2 - 1, file_len / 2 + 1);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
     }
 
     #[tokio::test]
     async fn test_range_single_byte_at_various_positions() {
-        // Test requesting single bytes at various positions in the file.
         let (client, file_contents) = setup_test_file(&[(1, (0, 5))]).await;
         let file_len = file_contents.data.len() as u64;
 
-        // First byte
         retrieve_and_verify(&client, &file_contents, Some(FileRange::new(0, 1))).await;
 
-        // Last byte
         retrieve_and_verify(&client, &file_contents, Some(FileRange::new(file_len - 1, file_len))).await;
 
-        // Middle byte
         let mid = file_len / 2;
         retrieve_and_verify(&client, &file_contents, Some(FileRange::new(mid, mid + 1))).await;
     }
 
     #[tokio::test]
     async fn test_multi_term_range_ends_mid_chunk() {
-        // Test with multiple terms where the requested range ends in the middle of the last term's chunk.
         let (client, file_contents) = setup_test_file(&[(1, (0, 3)), (2, (0, 3)), (3, (0, 3))]).await;
         let file_len = file_contents.data.len() as u64;
 
-        // End a few bytes before the file end
         let range = FileRange::new(0, file_len - 5);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
     }
 
     #[tokio::test]
     async fn test_multi_term_range_starts_mid_chunk() {
-        // Test with multiple terms where the requested range starts in the middle of the first term's chunk.
         let (client, file_contents) = setup_test_file(&[(1, (0, 3)), (2, (0, 3)), (3, (0, 3))]).await;
         let file_len = file_contents.data.len() as u64;
 
-        // Start a few bytes after the file start
         let range = FileRange::new(5, file_len);
         retrieve_and_verify(&client, &file_contents, Some(range)).await;
     }
+
+    // ==================== Multi-Disjoint Range Edge Cases ====================
+
+    /// Single xorb with three disjoint chunk ranges.
+    /// This creates one XorbBlock with chunk_ranges = [(0,2), (4,6), (8,10)].
+    #[tokio::test]
+    async fn test_triple_disjoint_same_xorb() {
+        let (client, file_contents) = setup_test_file(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))]).await;
+        retrieve_and_verify(&client, &file_contents, None).await;
+    }
+
+    /// Triple disjoint ranges with a partial byte range spanning the gap.
+    #[tokio::test]
+    async fn test_triple_disjoint_partial_range_across_gap() {
+        let (client, file_contents) = setup_test_file(&[(1, (0, 2)), (1, (4, 6)), (1, (8, 10))]).await;
+        let file_len = file_contents.data.len() as u64;
+        let range = FileRange::new(file_len / 4, file_len * 3 / 4);
+        retrieve_and_verify(&client, &file_contents, Some(range)).await;
+    }
+
+    /// Two xorbs, each with two disjoint ranges, interleaved in file order.
+    #[tokio::test]
+    async fn test_two_xorbs_interleaved_disjoint() {
+        let term_spec = &[(1, (0, 2)), (2, (0, 2)), (1, (4, 6)), (2, (4, 6))];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        retrieve_and_verify(&client, &file_contents, None).await;
+    }
+
+    /// Two xorbs interleaved with disjoint ranges, partial byte range.
+    #[tokio::test]
+    async fn test_two_xorbs_interleaved_disjoint_partial() {
+        let term_spec = &[(1, (0, 2)), (2, (0, 2)), (1, (4, 6)), (2, (4, 6))];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        let file_len = file_contents.data.len() as u64;
+        retrieve_and_verify(&client, &file_contents, Some(FileRange::new(file_len / 3, file_len * 2 / 3))).await;
+    }
+
+    /// Single xorb with four disjoint ranges, each a single chunk wide.
+    #[tokio::test]
+    async fn test_four_single_chunk_disjoint() {
+        let term_spec = &[(1, (0, 1)), (1, (3, 4)), (1, (6, 7)), (1, (9, 10))];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        retrieve_and_verify(&client, &file_contents, None).await;
+    }
+
+    /// Mix of contiguous and disjoint ranges from the same xorb.
+    /// Chunks 0-4 are contiguous, then a gap, then chunk 8-10.
+    #[tokio::test]
+    async fn test_contiguous_then_disjoint() {
+        let term_spec = &[(1, (0, 2)), (1, (2, 4)), (1, (8, 10))];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        retrieve_and_verify(&client, &file_contents, None).await;
+    }
+
+    /// Three xorbs with complex disjoint access patterns.
+    #[tokio::test]
+    async fn test_three_xorbs_complex_disjoint() {
+        let term_spec = &[
+            (1, (0, 2)),
+            (2, (0, 3)),
+            (3, (2, 5)),
+            (1, (5, 8)),
+            (2, (6, 8)),
+            (3, (0, 2)),
+        ];
+        let (client, file_contents) = setup_test_file(term_spec).await;
+        retrieve_and_verify(&client, &file_contents, None).await;
+    }
 }

xet_data/src/file_reconstruction/reconstruction_terms/retrieval_urls.rs

@@ -21,9 +21,11 @@ pub struct TermBlockRetrievalURLs {
     // which may be smaller than the originally requested range if the file ends early.
     pub byte_range: FileRange,
 
-    // The xorb retreival URLs.  These could be refreshed if need be.
+    // The xorb retrieval URLs.  These could be refreshed if need be.
     // Indexed by xorb_block_index stored in each XorbBlock.
-    pub(crate) xorb_block_retrieval_urls: RwLock<(UniqueId, Vec<(String, HttpRange)>)>,
+    // Each entry is (url, http_ranges) to support multi-range V2 blocks.
+    #[allow(clippy::type_complexity)]
+    pub(crate) xorb_block_retrieval_urls: RwLock<(UniqueId, Vec<(String, Vec<HttpRange>)>)>,
 }
 
 impl TermBlockRetrievalURLs {
@@ -32,7 +34,7 @@ impl TermBlockRetrievalURLs {
         file_hash: MerkleHash,
         byte_range: FileRange,
         acquisition_id: UniqueId,
-        retrieval_urls: Vec<(String, HttpRange)>,
+        retrieval_urls: Vec<(String, Vec<HttpRange>)>,
     ) -> Self {
         Self {
             file_hash,
@@ -41,15 +43,13 @@ impl TermBlockRetrievalURLs {
         }
     }
 
-    /// Gets the retrieval URL for a given xorb block.  All URL requests go through
-    /// this method in order to manage url refreshes; this function returns the
-    /// most recent retrieval URL in the case of a refresh.
-    pub async fn get_retrieval_url(&self, xorb_block_index: usize) -> (UniqueId, String, HttpRange) {
+    /// Gets the retrieval URL and all byte ranges for a given xorb block.
+    /// All URL requests go through this method in order to manage URL refreshes;
+    /// this function returns the most recent retrieval URL in the case of a refresh.
+    pub async fn get_retrieval_url(&self, xorb_block_index: usize) -> (UniqueId, String, Vec<HttpRange>) {
         let xbru = self.xorb_block_retrieval_urls.read().await;
-
-        let (url, url_range) = xbru.1[xorb_block_index].clone();
-
-        (xbru.0, url, url_range)
+        let (url, url_ranges) = &xbru.1[xorb_block_index];
+        (xbru.0, url.clone(), url_ranges.clone())
     }
 
     /// Refresh the retrieval URLs for all xorb blocks in this block.
@@ -61,8 +61,7 @@ impl TermBlockRetrievalURLs {
     /// the new request will get a new URL.  
     pub async fn refresh_retrieval_urls(&self, client: Arc<dyn Client>, acquisition_id: UniqueId) -> Result<()> {
         if self.xorb_block_retrieval_urls.read().await.0 != acquisition_id {
-            // This means another process has got in here while we're waiting for the lock and
-            // refreshed them.
+            // Another task already refreshed while we were waiting for the read lock.
             debug!(
                 file_hash = %self.file_hash,
                 byte_range = ?(self.byte_range.start, self.byte_range.end),
@@ -74,7 +73,7 @@ impl TermBlockRetrievalURLs {
         let mut retrieval_urls = self.xorb_block_retrieval_urls.write().await;
 
         if retrieval_urls.0 != acquisition_id {
-            // It's already been refreshed by another process.
+            // Already refreshed by another task while waiting for the write lock.
             debug!(
                 file_hash = %self.file_hash,
                 byte_range = ?(self.byte_range.start, self.byte_range.end),
@@ -90,8 +89,7 @@ impl TermBlockRetrievalURLs {
             "Refreshing expired retrieval URLs"
         );
 
-        // Since this hopefully doesn't happen too often, go through and retrieve an
-        // entire new block, then make sure everything matches up and take in the new stuff.
+        // Re-fetch the entire block to get fresh URLs, then verify the structure matches.
         let Some((returned_range, _transfer_bytes, file_terms)) =
             retrieve_file_term_block(client, self.file_hash, self.byte_range).await?
         else {
@@ -141,11 +139,13 @@ pub struct XorbURLProvider {
 
 #[async_trait::async_trait]
 impl URLProvider for XorbURLProvider {
-    async fn retrieve_url(&self) -> std::result::Result<(String, HttpRange), xet_client::cas_client::CasClientError> {
-        let (unique_id, url, http_range) = self.url_info.get_retrieval_url(self.xorb_block_index).await;
+    async fn retrieve_url(
+        &self,
+    ) -> std::result::Result<(String, Vec<HttpRange>), xet_client::cas_client::CasClientError> {
+        let (unique_id, url, http_ranges) = self.url_info.get_retrieval_url(self.xorb_block_index).await;
         *self.last_acquisition_id.lock().await = unique_id;
 
-        Ok((url, http_range))
+        Ok((url, http_ranges))
     }
 
     async fn refresh_url(&self) -> std::result::Result<(), xet_client::cas_client::CasClientError> {
@@ -155,3 +155,110 @@ impl URLProvider for XorbURLProvider {
             .map_err(|e| xet_client::cas_client::CasClientError::Other(e.to_string()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use tokio::sync::Mutex;
+    use xet_client::cas_client::{ClientTestingUtils, LocalClient, URLProvider};
+    use xet_client::cas_types::{FileRange, HttpRange};
+    use xet_core_structures::merklehash::MerkleHash;
+    use xet_runtime::utils::UniqueId;
+
+    use super::{TermBlockRetrievalURLs, XorbURLProvider};
+
+    fn sample_urls(n: usize) -> Vec<(String, Vec<HttpRange>)> {
+        (0..n)
+            .map(|i| (format!("https://example.com/xorb_{i}"), vec![HttpRange::new(0, 100)]))
+            .collect()
+    }
+
+    #[tokio::test]
+    async fn test_new_and_get_retrieval_url() {
+        let id = UniqueId::new();
+        let urls = sample_urls(3);
+        let block = TermBlockRetrievalURLs::new(MerkleHash::default(), FileRange::new(0, 100), id, urls.clone());
+
+        for (i, expected) in urls.iter().enumerate() {
+            let (ret_id, url, ranges) = block.get_retrieval_url(i).await;
+            assert!(ret_id == id, "acquisition ID mismatch for block {i}");
+            assert_eq!(url, expected.0);
+            assert_eq!(ranges, expected.1);
+        }
+    }
+
+    #[tokio::test]
+    async fn test_refresh_skipped_when_already_refreshed() {
+        let (client, file_contents) = {
+            let c = LocalClient::temporary().await.unwrap();
+            let fc = c.upload_random_file(&[(1, (0, 3))], 64).await.unwrap();
+            (c, fc)
+        };
+
+        let file_range = FileRange::new(0, file_contents.data.len() as u64);
+        let dyn_client: Arc<dyn xet_client::cas_client::Client> = client.clone();
+
+        let (_, _, file_terms) =
+            super::retrieve_file_term_block(dyn_client.clone(), file_contents.file_hash, file_range)
+                .await
+                .unwrap()
+                .unwrap();
+
+        let url_info = file_terms[0].url_info.clone();
+
+        // Get original acquisition ID
+        let (original_id, _, _) = url_info.get_retrieval_url(0).await;
+
+        // Refresh with a stale (different) ID should be a no-op.
+        let stale_id = UniqueId::new();
+        url_info.refresh_retrieval_urls(dyn_client.clone(), stale_id).await.unwrap();
+        let (id_after, _, _) = url_info.get_retrieval_url(0).await;
+        assert!(id_after == original_id, "refresh with stale ID should not change acquisition ID");
+
+        // Refresh with the correct ID should update URLs.
+        url_info.refresh_retrieval_urls(dyn_client.clone(), original_id).await.unwrap();
+        let (refreshed_id, _, _) = url_info.get_retrieval_url(0).await;
+        assert!(refreshed_id != original_id, "refresh with correct ID should change acquisition ID");
+    }
+
+    #[tokio::test]
+    async fn test_xorb_url_provider_retrieve_and_refresh() {
+        let (client, file_contents) = {
+            let c = LocalClient::temporary().await.unwrap();
+            let fc = c.upload_random_file(&[(1, (0, 3))], 64).await.unwrap();
+            (c, fc)
+        };
+
+        let file_range = FileRange::new(0, file_contents.data.len() as u64);
+        let dyn_client: Arc<dyn xet_client::cas_client::Client> = client.clone();
+
+        let (_, _, file_terms) =
+            super::retrieve_file_term_block(dyn_client.clone(), file_contents.file_hash, file_range)
+                .await
+                .unwrap()
+                .unwrap();
+
+        let url_info = file_terms[0].url_info.clone();
+
+        let provider = XorbURLProvider {
+            client: dyn_client.clone(),
+            url_info,
+            xorb_block_index: 0,
+            last_acquisition_id: Mutex::new(UniqueId::null()),
+        };
+
+        // retrieve_url should succeed and return a valid URL.
+        let (url, ranges) = provider.retrieve_url().await.unwrap();
+        assert!(!url.is_empty());
+        assert!(!ranges.is_empty());
+
+        // refresh_url should succeed (refreshes with the current acquisition ID).
+        provider.refresh_url().await.unwrap();
+
+        // After refresh, retrieve_url should still work with updated URLs.
+        let (url2, ranges2) = provider.retrieve_url().await.unwrap();
+        assert!(!url2.is_empty());
+        assert!(!ranges2.is_empty());
+    }
+}

xet_data/src/file_reconstruction/reconstruction_terms/xorb_block.rs

@@ -13,27 +13,49 @@ use super::retrieval_urls::{TermBlockRetrievalURLs, XorbURLProvider};
 use crate::progress_tracking::download_tracking::DownloadTaskUpdater;
 
 /// Downloaded and decompressed data for a xorb block, including chunk boundary offsets.
+///
+/// A single `XorbBlockData` may hold data from multiple disjoint chunk ranges
+/// (V2 multi-range fetch). The chunks are concatenated in range order, and
+/// `chunk_offsets` maps each chunk index to its byte position within `data`.
 pub struct XorbBlockData {
-    pub chunk_offsets: Vec<usize>,
-    pub uncompressed_size: u64,
+    /// Pairs of (chunk_index, byte_offset) mapping each chunk to its start position
+    /// within `data`. Because the block can span multiple disjoint chunk ranges,
+    /// storing the chunk index alongside the offset avoids ambiguity.
+    pub chunk_offsets: Vec<(usize, usize)>,
+
+    /// The concatenated decompressed chunk data for all ranges in this block.
     pub data: Bytes,
 }
 
+/// A reference from a file term back to the xorb block it belongs to.
+/// Used by `determine_size_if_possible` to check whether the block's total
+/// uncompressed size can be inferred from the terms that reference it.
 #[derive(Debug)]
 pub struct XorbReference {
+    /// The chunk range within the xorb that this file term covers.
     pub term_chunks: ChunkRange,
+    /// The uncompressed byte size of this term's data.
     pub uncompressed_size: usize,
 }
 
-/// A downloadable xorb block identified by hash and chunk range, with cached data.
-/// Multiple file terms may reference the same xorb block.
+/// A downloadable xorb block identified by hash and chunk ranges, with cached data.
+///
+/// A block may contain multiple disjoint chunk ranges from the same xorb (V2 multi-range).
+/// Multiple file terms may reference the same block. Downloaded data is cached in `data`
+/// so that the first term to request it triggers the download, and subsequent terms
+/// reuse the cached result.
 pub struct XorbBlock {
     pub xorb_hash: MerkleHash,
-    pub chunk_range: ChunkRange,
+    /// The chunk ranges fetched for this block. For V1 this is a single range;
+    /// for V2 multi-range fetches this may contain multiple disjoint ranges.
+    pub chunk_ranges: Vec<ChunkRange>,
+    /// Index into the parent `TermBlockRetrievalURLs` for URL lookup.
     pub xorb_block_index: usize,
-    /// All file-term chunk ranges covered by this xorb block, sorted by range start.
+    /// All file-term references covered by this block, sorted by chunk range start.
+    /// Populated during `retrieve_file_term_block` and used to compute `uncompressed_size_if_known`.
     pub references: Vec<XorbReference>,
-    /// Expected decompressed size of the block when known. Used for debug_assert in clients.
+    /// Expected total decompressed size across all chunk ranges, if it can be determined
+    /// from the references. Passed to clients as a debug assertion hint.
     pub uncompressed_size_if_known: Option<usize>,
     pub data: OnceCell<Arc<XorbBlockData>>,
 }
@@ -41,7 +63,7 @@ pub struct XorbBlock {
 impl PartialEq for XorbBlock {
     fn eq(&self, other: &Self) -> bool {
         self.xorb_hash == other.xorb_hash
-            && self.chunk_range == other.chunk_range
+            && self.chunk_ranges == other.chunk_ranges
             && self.xorb_block_index == other.xorb_block_index
     }
 }
@@ -63,6 +85,7 @@ impl XorbBlock {
     ) -> Result<Arc<XorbBlockData>> {
         let xorb_block_index = self.xorb_block_index;
         let uncompressed_size_if_known = self.uncompressed_size_if_known;
+        let chunk_ranges = self.chunk_ranges.clone();
 
         self.data
             .get_or_try_init(|| async {
@@ -89,14 +112,18 @@ impl XorbBlock {
                     .get_file_term_data(Box::new(url_provider), permit, progress_callback, uncompressed_size_if_known)
                     .await?;
 
-                let chunk_offsets: Vec<usize> = chunk_byte_offsets.iter().map(|&x| x as usize).collect();
-                let uncompressed_size = data.len() as u64;
+                // Build chunk_offsets by zipping each chunk index (from all chunk_ranges)
+                // with the corresponding byte offset from the returned data.
+                let mut chunk_offsets = Vec::new();
+                let mut offset_idx = 0;
+                for range in &chunk_ranges {
+                    for chunk_idx in range.start..range.end {
+                        chunk_offsets.push((chunk_idx as usize, chunk_byte_offsets[offset_idx] as usize));
+                        offset_idx += 1;
+                    }
+                }
 
-                Ok(Arc::new(XorbBlockData {
-                    chunk_offsets,
-                    uncompressed_size,
-                    data,
-                }))
+                Ok(Arc::new(XorbBlockData { chunk_offsets, data }))
             })
             .await
             .cloned()
@@ -105,33 +132,67 @@ impl XorbBlock {
     /// Determines the total uncompressed size of the xorb block from the reference terms,
     /// if possible.
     ///
-    /// The size can be determined when:
-    /// 1. A single term's chunk range exactly matches the full xorb range, or
-    /// 2. A chain of term chunk ranges exactly covers the full xorb range with no gaps (e.g. [0..3, 3..5] covers 0..5).
+    /// Uses a forward-chaining DP: starting from the first chunk range's start,
+    /// we track which chunk positions are "reachable" (i.e., fully covered by a
+    /// contiguous chain of terms) along with the accumulated uncompressed size.
     ///
-    /// The `terms` slice must be sorted by chunk range start index.
-    pub fn determine_size_if_possible(xorb_range: ChunkRange, terms: &[XorbReference]) -> Option<usize> {
+    /// For multi-range blocks with disjoint chunk ranges (e.g. `[0,3)` and `[5,8)`),
+    /// the gaps between ranges are inserted as zero-cost bridges. This lets the DP
+    /// traverse the full set of ranges in a single pass — a gap `[3,5)` contributes
+    /// no data but connects the end of one range to the start of the next.
+    ///
+    /// Returns `Some(total_size)` if every range is fully covered, `None` otherwise.
+    ///
+    /// The `terms` slice must be sorted by `term_chunks.start`.
+    pub fn determine_size_if_possible(xorb_ranges: &[ChunkRange], terms: &[XorbReference]) -> Option<usize> {
         debug_assert!(
             terms.windows(2).all(|w| w[0].term_chunks.start <= w[1].term_chunks.start),
             "terms must be sorted by chunk range start"
         );
 
-        // DP approach: track which chunk endpoints are reachable from xorb_range.start
-        // via contiguous chains, along with accumulated uncompressed sizes.
-        // This correctly handles multiple terms with the same start index by
-        // considering all possible chain continuations.
-        let mut reachable: BTreeMap<u32, usize> = BTreeMap::new();
-        reachable.insert(xorb_range.start, 0);
+        debug_assert!(
+            terms.iter().all(|term| xorb_ranges
+                .iter()
+                .any(|r| term.term_chunks.start >= r.start && term.term_chunks.end <= r.end)),
+            "all terms must fall within one of the xorb ranges"
+        );
 
+        if xorb_ranges.is_empty() {
+            return Some(0);
+        }
+
+        // Build a lookup from range-end -> next-range-start for gap bridging.
+        // E.g. for ranges [0,3) and [5,8), maps 3 -> 5, meaning once chunk 3
+        // is reachable we can bridge to chunk 5 at zero cost.
+        let gap_bridges: BTreeMap<u32, u32> = xorb_ranges
+            .windows(2)
+            .filter(|pair| pair[0].end < pair[1].start)
+            .map(|pair| (pair[0].end, pair[1].start))
+            .collect();
+
+        // DP map: chunk position -> accumulated uncompressed size to reach that position.
+        // Seed with the start of the first range.
+        let mut reachable: BTreeMap<u32, usize> = BTreeMap::new();
+        reachable.insert(xorb_ranges[0].start, 0);
+
+        // Process terms in sorted order, extending reachable positions.
         for term in terms {
             if let Some(&accumulated) = reachable.get(&term.term_chunks.start) {
-                reachable
-                    .entry(term.term_chunks.end)
-                    .or_insert(accumulated + term.uncompressed_size);
+                let new_end = term.term_chunks.end;
+                let new_size = accumulated + term.uncompressed_size;
+
+                reachable.entry(new_end).or_insert(new_size);
+
+                // If this term reaches the end of a range that has a gap bridge,
+                // make the start of the next range reachable at the same accumulated size.
+                if let Some(&bridge_target) = gap_bridges.get(&new_end) {
+                    reachable.entry(bridge_target).or_insert(new_size);
+                }
             }
         }
 
-        reachable.get(&xorb_range.end).copied()
+        // The block is fully covered if we can reach the end of the last range.
+        reachable.get(&xorb_ranges.last().unwrap().end).copied()
     }
 }
 
@@ -153,197 +214,210 @@ mod tests {
 
     #[test]
     fn test_single_term_exact_match() {
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[(ChunkRange::new(0, 5), 1000)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(1000));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(1000));
     }
 
     #[test]
     fn test_two_terms_chained() {
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[(ChunkRange::new(0, 3), 600), (ChunkRange::new(3, 5), 400)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(1000));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(1000));
     }
 
     #[test]
     fn test_three_terms_chained() {
-        let xorb_range = ChunkRange::new(0, 6);
+        let ranges = &[ChunkRange::new(0, 6)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 2), 200),
             (ChunkRange::new(2, 4), 300),
             (ChunkRange::new(4, 6), 500),
         ]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(1000));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(1000));
     }
 
     #[test]
     fn test_gap_in_chain() {
-        let xorb_range = ChunkRange::new(0, 6);
+        let ranges = &[ChunkRange::new(0, 6)];
         let terms = build_refs(&[(ChunkRange::new(0, 2), 200), (ChunkRange::new(4, 6), 500)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_does_not_start_at_xorb_start() {
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[(ChunkRange::new(1, 5), 800)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_does_not_end_at_xorb_end() {
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[(ChunkRange::new(0, 3), 600)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_empty_terms() {
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms: Vec<XorbReference> = vec![];
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_overlapping_terms_with_exact_cover() {
         // Terms [0..3, 1..4, 3..5] - the chain 0..3, 3..5 covers 0..5.
         // The overlapping term 1..4 should be skipped.
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 3), 600),
             (ChunkRange::new(1, 4), 700),
             (ChunkRange::new(3, 5), 400),
         ]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(1000));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(1000));
     }
 
     #[test]
     fn test_duplicate_terms_first_covers() {
         // Two identical terms covering the full range.
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[(ChunkRange::new(0, 5), 1000), (ChunkRange::new(0, 5), 1000)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(1000));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(1000));
     }
 
     #[test]
     fn test_nonzero_xorb_start() {
-        let xorb_range = ChunkRange::new(3, 8);
+        let ranges = &[ChunkRange::new(3, 8)];
         let terms = build_refs(&[(ChunkRange::new(3, 5), 400), (ChunkRange::new(5, 8), 600)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(1000));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(1000));
     }
 
     #[test]
     fn test_nonzero_xorb_start_no_match() {
-        let xorb_range = ChunkRange::new(3, 8);
+        let ranges = &[ChunkRange::new(3, 8)];
         let terms = build_refs(&[(ChunkRange::new(3, 5), 400)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_single_chunk_range() {
-        let xorb_range = ChunkRange::new(0, 1);
+        let ranges = &[ChunkRange::new(0, 1)];
         let terms = build_refs(&[(ChunkRange::new(0, 1), 42)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(42));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(42));
     }
 
     #[test]
-    fn test_chain_with_extra_terms_before_and_after() {
-        // Extra terms that don't participate in the chain but are within the sorted list.
-        let xorb_range = ChunkRange::new(2, 8);
+    fn test_chain_with_overlapping_inner_terms() {
+        let ranges = &[ChunkRange::new(2, 8)];
+        // The overlapping term [3,6) is within the range but doesn't form
+        // a better chain than [2,5) + [5,8), so it's harmlessly ignored.
         let terms = build_refs(&[
-            (ChunkRange::new(0, 2), 100),  // before xorb range
-            (ChunkRange::new(2, 5), 500),  // chain start
-            (ChunkRange::new(3, 6), 999),  // overlapping, skipped
-            (ChunkRange::new(5, 8), 300),  // chain end
-            (ChunkRange::new(8, 10), 200), // after xorb range
+            (ChunkRange::new(2, 5), 500),
+            (ChunkRange::new(3, 6), 999),
+            (ChunkRange::new(5, 8), 300),
         ]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(800));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(800));
     }
 
     #[test]
     fn test_partial_overlap_no_cover() {
         // Terms partially overlap but don't form a contiguous chain covering the full range.
-        let xorb_range = ChunkRange::new(0, 10);
+        let ranges = &[ChunkRange::new(0, 10)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 4), 400),
             (ChunkRange::new(3, 7), 400),
             (ChunkRange::new(6, 10), 400),
         ]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_same_start_short_then_long_covering_full() {
         // Short range first, then a long range that covers the full xorb.
-        let xorb_range = ChunkRange::new(0, 5);
+        let ranges = &[ChunkRange::new(0, 5)];
         let terms = build_refs(&[(ChunkRange::new(0, 3), 300), (ChunkRange::new(0, 5), 500)]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(500));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(500));
     }
 
     #[test]
     fn test_same_start_short_then_long_with_chain() {
         // Short range first, then a longer range, where the short range can also chain.
-        let xorb_range = ChunkRange::new(0, 6);
+        // Chain via 0..3 + 3..6 = 600
+        let ranges = &[ChunkRange::new(0, 6)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 2), 200),
             (ChunkRange::new(0, 3), 300),
             (ChunkRange::new(3, 6), 300),
         ]);
-        // Chain via 0..3 + 3..6 = 600
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(600));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(600));
     }
 
     #[test]
     fn test_same_start_multiple_duplicates_chain_through_second() {
         // Multiple terms at start 0 with different lengths; only the middle one chains.
-        let xorb_range = ChunkRange::new(0, 6);
+        // Chain via 0..4 + 4..6 = 600
+        let ranges = &[ChunkRange::new(0, 6)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 2), 200),
             (ChunkRange::new(0, 4), 400),
             (ChunkRange::new(0, 5), 500),
             (ChunkRange::new(4, 6), 200),
         ]);
-        // Chain via 0..4 + 4..6 = 600
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(600));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(600));
     }
 
     #[test]
     fn test_same_start_at_midpoint() {
         // Duplicate starts at a midpoint in the chain, not just at the beginning.
-        let xorb_range = ChunkRange::new(0, 8);
+        // Chain via 0..3 + 3..6 + 6..8 = 800
+        let ranges = &[ChunkRange::new(0, 8)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 3), 300),
             (ChunkRange::new(3, 5), 200),
             (ChunkRange::new(3, 6), 300),
             (ChunkRange::new(6, 8), 200),
         ]);
-        // Chain via 0..3 + 3..6 + 6..8 = 800
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(800));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(800));
     }
 
     #[test]
     fn test_same_start_none_covers() {
         // Multiple terms at start 0, but none chain to cover the full range.
-        let xorb_range = ChunkRange::new(0, 10);
+        let ranges = &[ChunkRange::new(0, 10)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 2), 200),
             (ChunkRange::new(0, 4), 400),
             (ChunkRange::new(0, 6), 600),
         ]);
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), None);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 
     #[test]
     fn test_same_start_two_groups_chained() {
         // Two groups of duplicate-start terms that chain together.
-        let xorb_range = ChunkRange::new(0, 6);
+        // Chain via 0..3 + 3..6 = 600
+        let ranges = &[ChunkRange::new(0, 6)];
         let terms = build_refs(&[
             (ChunkRange::new(0, 2), 200),
             (ChunkRange::new(0, 3), 300),
             (ChunkRange::new(3, 5), 200),
             (ChunkRange::new(3, 6), 300),
         ]);
-        // Chain via 0..3 + 3..6 = 600
-        assert_eq!(XorbBlock::determine_size_if_possible(xorb_range, &terms), Some(600));
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(600));
+    }
+
+    #[test]
+    fn test_multiple_disjoint_ranges_both_covered() {
+        let ranges = &[ChunkRange::new(0, 3), ChunkRange::new(5, 8)];
+        let terms = build_refs(&[(ChunkRange::new(0, 3), 300), (ChunkRange::new(5, 8), 400)]);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), Some(700));
+    }
+
+    #[test]
+    fn test_multiple_disjoint_ranges_one_uncovered() {
+        let ranges = &[ChunkRange::new(0, 3), ChunkRange::new(5, 8)];
+        let terms = build_refs(&[(ChunkRange::new(0, 3), 300)]);
+        assert_eq!(XorbBlock::determine_size_if_possible(ranges, &terms), None);
     }
 }

xet_data/src/processing/bin/xtool.rs

@@ -7,8 +7,8 @@ use anyhow::Result;
 use clap::{Args, Parser, Subcommand};
 use http::header::{self, HeaderMap, HeaderValue};
 use walkdir::WalkDir;
+use xet_client::cas_client::RemoteClient;
 use xet_client::cas_client::auth::TokenRefresher;
-use xet_client::cas_client::{Client, RemoteClient};
 use xet_client::cas_types::{FileRange, QueryReconstructionResponse};
 use xet_client::hub_client::{BearerCredentialHelper, HubClient, Operation, RepoInfo};
 use xet_core_structures::merklehash::MerkleHash;
@@ -230,8 +230,9 @@ async fn query_reconstruction(
         cas_storage_config.custom_headers.clone(),
     );
 
+    // Use V1 directly so the query tool returns the raw QueryReconstructionResponse for inspection.
     remote_client
-        .get_reconstruction(&file_hash, bytes_range)
+        .get_reconstruction_v1(&file_hash, bytes_range)
         .await
         .map_err(anyhow::Error::from)
 }

xet_data/src/processing/test_utils.rs

@@ -15,6 +15,48 @@ use super::file_cleaner::Sha256Policy;
 use super::{FileDownloadSession, FileUploadSession, XetFileInfo};
 use crate::progress_tracking::TrackingProgressUpdater;
 
+/// Describes how hydration (download/smudge) should be performed during a test.
+///
+/// Each variant exercises a different reconstruction path:
+/// - `DirectClient`: Uses `LocalClient` directly (no HTTP server).
+/// - `ServerV2`: Uses `LocalTestServer` with default V2 reconstruction.
+/// - `ServerV1Fallback`: Uses `LocalTestServer` with V2 disabled, forcing V1 fallback.
+/// - `ServerMaxRanges2`: Uses `LocalTestServer` with `max_ranges_per_fetch=2`, forcing multi-range fetch splitting in
+///   V2 responses.
+#[derive(Debug, Clone, Copy)]
+pub enum HydrationMode {
+    DirectClient,
+    ServerV2,
+    ServerV1Fallback,
+    ServerMaxRanges2,
+}
+
+impl HydrationMode {
+    pub fn all() -> &'static [HydrationMode] {
+        &[
+            HydrationMode::DirectClient,
+            HydrationMode::ServerV2,
+            HydrationMode::ServerV1Fallback,
+            HydrationMode::ServerMaxRanges2,
+        ]
+    }
+
+    pub fn uses_server(&self) -> bool {
+        !matches!(self, HydrationMode::DirectClient)
+    }
+}
+
+impl std::fmt::Display for HydrationMode {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            HydrationMode::DirectClient => write!(f, "direct_client"),
+            HydrationMode::ServerV2 => write!(f, "server_v2"),
+            HydrationMode::ServerV1Fallback => write!(f, "server_v1_fallback"),
+            HydrationMode::ServerMaxRanges2 => write!(f, "server_max_ranges_2"),
+        }
+    }
+}
+
 /// Creates or overwrites a single file in `dir` with `size` bytes of random data.
 /// Panics on any I/O error. Returns the total number of bytes written (=`size`).
 pub fn create_random_file(path: impl AsRef<Path>, size: usize, seed: u64) -> usize {
@@ -174,6 +216,44 @@ impl HydrateDehydrateTest {
         }
     }
 
+    /// Creates a new test harness configured for a specific hydration mode.
+    pub fn for_mode(mode: HydrationMode) -> Self {
+        Self::new(mode.uses_server())
+    }
+
+    /// Applies hydration mode configuration to the test server.
+    /// Must be called after `dehydrate()` and before `hydrate()`.
+    pub async fn apply_hydration_mode(&mut self, mode: HydrationMode) {
+        match mode {
+            HydrationMode::DirectClient => {},
+            HydrationMode::ServerV2 => {
+                self.ensure_server_created().await;
+            },
+            HydrationMode::ServerV1Fallback => {
+                self.ensure_server_created().await;
+                self.test_server.as_ref().unwrap().client().disable_v2_reconstruction(404);
+            },
+            HydrationMode::ServerMaxRanges2 => {
+                self.ensure_server_created().await;
+                self.test_server.as_ref().unwrap().client().set_max_ranges_per_fetch(2);
+            },
+        }
+    }
+
+    /// Ensures the test server is running, creating it if necessary.
+    /// Call this before configuring the server (e.g., disabling V2 or setting max ranges).
+    pub async fn ensure_server_created(&mut self) {
+        if self.use_test_server && self.test_server.is_none() {
+            let local_client = LocalClient::new(self.cas_dir.join("xet/xorbs")).await.unwrap();
+            self.test_server = Some(LocalTestServerBuilder::new().with_client(local_client).start().await);
+        }
+    }
+
+    /// Returns a reference to the test server, if one has been created.
+    pub fn test_server(&self) -> Option<&LocalTestServer> {
+        self.test_server.as_ref()
+    }
+
     /// Lazily initializes the test server (if needed) and returns a CAS client.
     async fn get_or_create_client(&mut self) -> Arc<dyn Client> {
         if self.use_test_server {

xet_data/tests/test_clean_smudge.rs

@@ -10,18 +10,25 @@ test_set_constants! {
     MAX_XORB_CHUNKS = 8;
 }
 
-/// Runs clean/smudge test with all combinations of (use_test_server, sequential).
+/// Runs clean/smudge test with all combinations of (hydration_mode, sequential).
 /// Each combination runs sequentially with its own HydrateDehydrateTest instance to avoid
 /// too many open files.
+///
+/// This exercises every hydration path for every test case:
+/// - DirectClient: LocalClient without a server
+/// - ServerV2: LocalTestServer with default V2 reconstruction
+/// - ServerV1Fallback: LocalTestServer with V2 disabled (tests V1-to-V2 conversion)
+/// - ServerMaxRanges2: LocalTestServer with max_ranges_per_fetch=2 (tests fetch splitting)
 pub async fn check_clean_smudge_files(file_list: &[(impl AsRef<str> + Clone, usize)]) {
-    for use_server in [false, true] {
+    for &mode in HydrationMode::all() {
         for sequential in [true, false] {
-            eprintln!("Testing use_test_server={use_server}, sequential={sequential}");
+            eprintln!("Testing mode={mode}, sequential={sequential}");
 
-            let mut ts = HydrateDehydrateTest::new(use_server);
+            let mut ts = HydrateDehydrateTest::for_mode(mode);
             create_random_files(&ts.src_dir, file_list, 0);
 
             ts.dehydrate(sequential).await;
+            ts.apply_hydration_mode(mode).await;
             ts.hydrate().await;
             ts.verify_src_dest_match();
             ts.hydrate_partitioned_writers(4).await;
@@ -35,18 +42,21 @@ pub async fn check_clean_smudge_files(file_list: &[(impl AsRef<str> + Clone, usi
 /// Helper for multipart tests:
 ///  - takes a slice of `(String, Vec<(u64, u64)>)` which fully specifies each file.
 ///  - for each file, calls `create_random_multipart_file` with the given segments.
+///
+/// Exercises all hydration modes just like `check_clean_smudge_files`.
 async fn check_clean_smudge_files_multipart(file_specs: &[(String, Vec<(usize, u64)>)]) {
-    for use_server in [false, true] {
+    for &mode in HydrationMode::all() {
         for sequential in [true, false] {
-            eprintln!("Testing use_test_server={use_server}, sequential={sequential}");
+            eprintln!("Testing mode={mode}, sequential={sequential}");
 
-            let mut ts = HydrateDehydrateTest::new(use_server);
+            let mut ts = HydrateDehydrateTest::for_mode(mode);
 
             for (file_name, segments) in file_specs {
                 create_random_multipart_file(ts.src_dir.join(file_name), segments);
             }
 
             ts.dehydrate(sequential).await;
+            ts.apply_hydration_mode(mode).await;
             ts.hydrate().await;
             ts.verify_src_dest_match();
             ts.hydrate_partitioned_writers(4).await;

xet_data/tests/test_clean_smudge_multirange.rs

@@ -0,0 +1,71 @@
+//! Clean/smudge integration tests with `enable_multirange_fetching = true`.
+//!
+//! This test binary is a separate copy of a subset of the clean/smudge tests
+//! that runs with `enable_multirange_fetching` enabled, exercising the
+//! multirange HTTP request path rather than the default single-range splitting.
+
+use xet_data::deduplication::constants::{MAX_XORB_BYTES, MAX_XORB_CHUNKS, TARGET_CHUNK_SIZE};
+use xet_data::processing::test_utils::*;
+use xet_runtime::{test_set_config, test_set_constants};
+
+test_set_constants! {
+    TARGET_CHUNK_SIZE = 1024;
+    MAX_XORB_BYTES = 5 * (*TARGET_CHUNK_SIZE);
+    MAX_XORB_CHUNKS = 8;
+}
+
+test_set_config! {
+    client {
+        enable_multirange_fetching = true;
+    }
+}
+
+#[cfg(test)]
+mod testing_clean_smudge_multirange {
+    use super::*;
+
+    pub async fn check_clean_smudge_files(file_list: &[(impl AsRef<str> + Clone, usize)]) {
+        for &mode in HydrationMode::all() {
+            for sequential in [true, false] {
+                eprintln!("Testing mode={mode}, sequential={sequential} (forced multirange)");
+
+                let mut ts = HydrateDehydrateTest::for_mode(mode);
+                create_random_files(&ts.src_dir, file_list, 0);
+
+                ts.dehydrate(sequential).await;
+                ts.apply_hydration_mode(mode).await;
+                ts.hydrate().await;
+                ts.verify_src_dest_match();
+            }
+        }
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_simple_directory() {
+        check_clean_smudge_files(&[("a", 16)]).await;
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_multiple() {
+        check_clean_smudge_files(&[("a", 16), ("b", 8)]).await;
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_single_large() {
+        check_clean_smudge_files(&[("a", *MAX_XORB_BYTES + 1)]).await;
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_multiple_large() {
+        check_clean_smudge_files(&[("a", *MAX_XORB_BYTES + 1), ("b", *MAX_XORB_BYTES + 2)]).await;
+    }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_many_small_multiple_xorbs() {
+        let n = 16;
+        let size = *MAX_XORB_BYTES / 8 + 1;
+
+        let files: Vec<_> = (0..n).map(|idx| (format!("f_{idx}"), size)).collect();
+        check_clean_smudge_files(&files).await;
+    }
+}

xet_runtime/src/config/groups/client.rs

@@ -217,7 +217,7 @@ crate::config_group!({
     /// The default value is 2.
     ///
     /// Use the environment variable `HF_XET_CLIENT_AC_INITIAL_UPLOAD_CONCURRENCY` to set this value.
-    ref ac_initial_upload_concurrency: usize = 1;
+    ref ac_initial_upload_concurrency: usize = 2;
 
     /// The maximum number of simultaneous download streams permitted by
     /// the adaptive concurrency control.
@@ -238,10 +238,10 @@ crate::config_group!({
     /// The starting number of concurrent download streams, which will increase up to max_concurrent_downloads
     /// on successful completions.
     ///
-    /// The default value is 1.
+    /// The default value is 4.
     ///
     /// Use the environment variable `HF_XET_CLIENT_AC_INITIAL_DOWNLOAD_CONCURRENCY` to set this value.
-    ref ac_initial_download_concurrency: usize = 1;
+    ref ac_initial_download_concurrency: usize = 4;
 
     /// Path to Unix domain socket for CAS HTTP connections.
     /// When set, all CAS HTTP traffic uses this socket instead of TCP.
@@ -252,4 +252,24 @@ crate::config_group!({
     /// Use the environment variable `HF_XET_CLIENT_UNIX_SOCKET_PATH` to set this value.
     ref unix_socket_path: Option<String> = None;
 
+    /// The reconstruction API version to request from the CAS server.
+    /// When set to 1 or 2, forces that version with no fallback.
+    /// When unset, auto-detects by trying V2 first, falling back to V1 on 404 or 501.
+    ///
+    /// The default value is None (auto-detect).
+    ///
+    /// Use the environment variable `HF_XET_CLIENT_RECONSTRUCTION_API_VERSION` to set this value.
+    ref reconstruction_api_version: Option<u32> = None;
+
+    /// Whether to use multi-range HTTP requests when fetching xorb data.
+    /// When false (default), V2 multi-range fetch entries are split into
+    /// individual single-range requests executed in parallel, which avoids
+    /// slow server-side multirange processing.
+    /// When true, multi-range requests are sent as-is.
+    ///
+    /// The default value is false.
+    ///
+    /// Use the environment variable `HF_XET_CLIENT_ENABLE_MULTIRANGE_FETCHING` to set this value.
+    ref enable_multirange_fetching: bool = false;
+
 });