diff --git a/docker-compose.dev.yml b/docker-compose.dev.yml
index 972d7ef8..e768f2b7 100644
--- a/docker-compose.dev.yml
+++ b/docker-compose.dev.yml
@@ -119,6 +119,61 @@ services:
       - qdrant
       - full
 
+  # OpenSearch k-NN (Phase 3 driver). Single-node dev profile with the
+  # security plugin disabled → plain HTTP on :9200, no auth/TLS. The image
+  # bundles the opensearch-knn plugin. For production use a secured,
+  # multi-node cluster. See docs/dev/opensearch-integration-test.md.
+  opensearch:
+    image: opensearchproject/opensearch:3.3.2
+    container_name: WeKnora-opensearch-dev
+    environment:
+      - discovery.type=single-node
+      # dev only: plain HTTP on :9200, no TLS/auth. The entrypoint script
+      # honours DISABLE_SECURITY_PLUGIN (env var) to skip both the demo
+      # install and the OPENSEARCH_INITIAL_ADMIN_PASSWORD requirement.
+      - DISABLE_SECURITY_PLUGIN=true
+      - DISABLE_INSTALL_DEMO_CONFIG=true
+      - OPENSEARCH_JAVA_OPTS=-Xms512m -Xmx512m
+      - bootstrap.memory_lock=true
+    ulimits:
+      memlock:
+        soft: -1
+        hard: -1
+    ports:
+      - "${OPENSEARCH_PORT:-9200}:9200"
+    volumes:
+      - opensearch_data_dev:/usr/share/opensearch/data
+    networks:
+      - WeKnora-network-dev
+    restart: unless-stopped
+    profiles:
+      - opensearch
+      - full
+      # Also a member of opensearch-ui so the Dashboards depends_on resolves
+      # when only that profile is active (`--profile opensearch-ui up`).
+      - opensearch-ui
+
+  # Optional UI for visual index/mapping/query inspection. Decoupled from the
+  # "opensearch" / "full" profiles so the heavy Dashboards container is never
+  # forced up alongside the cluster — the driver e2e is fully curl-verifiable
+  # against :9200. Start it on demand with `--profile opensearch-ui up -d`
+  # (depends_on pulls the cluster in automatically).
+  opensearch-dashboards:
+    image: opensearchproject/opensearch-dashboards:3.3.0
+    container_name: WeKnora-opensearch-dashboards-dev
+    environment:
+      - OPENSEARCH_HOSTS=["http://opensearch:9200"]
+      - DISABLE_SECURITY_DASHBOARDS_PLUGIN=true
+    ports:
+      - "${OPENSEARCH_DASHBOARDS_PORT:-5601}:5601"
+    networks:
+      - WeKnora-network-dev
+    depends_on:
+      - opensearch
+    restart: unless-stopped
+    profiles:
+      - opensearch-ui
+
   milvus:
     image: milvusdb/milvus:v2.6.11
     container_name: WeKnora-milvus-dev
@@ -468,6 +523,7 @@ volumes:
   neo4j-data-dev:
   jaeger_data_dev:
   qdrant_data_dev:
+  opensearch_data_dev:
   milvus_data_dev:
   docreader-tmp-dev:
   langfuse_clickhouse_data_dev:
diff --git a/docs/dev/opensearch-integration-test.md b/docs/dev/opensearch-integration-test.md
new file mode 100644
index 00000000..0edd5f1c
--- /dev/null
+++ b/docs/dev/opensearch-integration-test.md
@@ -0,0 +1,109 @@
+# OpenSearch k-NN driver — local integration test
+
+This guide brings up a single-node OpenSearch cluster and exercises the
+OpenSearch retrieve engine end to end. The driver lives in
+`internal/application/repository/retriever/opensearch/`.
+
+## 1. Start a dev cluster
+
+```bash
+docker compose -f docker-compose.dev.yml --profile opensearch up -d
+```
+
+This starts:
+
+- `opensearch` on `http://localhost:9200` — single-node, **security plugin
+  disabled** (plain HTTP, no auth/TLS). The image bundles the
+  `opensearch-knn` plugin.
+
+> **OpenSearch Dashboards is optional** and lives in a separate
+> `opensearch-ui` profile, so it is *not* started by `--profile opensearch`.
+> The whole integration test below is curl-verifiable against `:9200`. If you
+> want the web UI (Dev Tools console / visual index inspection), start it on
+> demand:
+>
+> ```bash
+> docker compose -f docker-compose.dev.yml --profile opensearch-ui up -d
+> # opensearch-dashboards on http://localhost:5601 (depends_on pulls the cluster in)
+> ```
+
+Verify:
+
+```bash
+curl -s localhost:9200 | jq '.version.distribution, .version.number'
+# "opensearch" "3.3.2"
+curl -s 'localhost:9200/_cat/plugins?format=json' | jq -r '.[].component' | grep opensearch-knn
+```
+
+> Production clusters must enable the security plugin (TLS + auth). The dev
+> profile disables it only to keep local setup trivial. When connecting to a
+> secured cluster, set `username` / `password` and — for self-signed certs in
+> dev only — `insecure_skip_verify=true`.
+
+## 2. Register the store
+
+### Option A — DB store (UI / API)
+
+`POST /api/v1/vector-stores`:
+
+```json
+{
+  "name": "opensearch-local",
+  "engine_type": "opensearch",
+  "connection_config": { "addr": "http://localhost:9200" },
+  "index_config": {
+    "number_of_shards": 1,
+    "number_of_replicas": 0,
+    "hnsw_m": 16,
+    "hnsw_ef_construction": 100,
+    "knn_engine": "lucene"
+  }
+}
+```
+
+`CreateStore` runs the connection probe (version + k-NN plugin) before
+persisting; a bad address / unsupported version / missing plugin is rejected
+with `400`.
+
+### Option B — env store
+
+```bash
+export RETRIEVE_DRIVER=opensearch
+export OPENSEARCH_ADDR=http://localhost:9200
+# export OPENSEARCH_USERNAME / OPENSEARCH_PASSWORD for a secured cluster
+# export OPENSEARCH_INSECURE_SKIP_VERIFY=true   # self-signed dev TLS only
+```
+
+## 3. Single-node note (important)
+
+On a single-node cluster, any index created with `number_of_replicas >= 1`
+leaves its replica shard **unassigned**, so the index health goes **Yellow**.
+Yellow does **not** block reads or writes — it is safe for local testing — but
+to keep the cluster Green set **`number_of_replicas: 0`** at store
+registration (as in the Option A example above). The driver default is `1`
+(it assumes a ≥2-node cluster).
+
+## 4. Exercise the flow
+
+1. Bind a knowledge base to the store and ingest a few documents.
+2. Confirm the per-dimension index appears:
+   `curl -s 'localhost:9200/_cat/indices?v' | grep weknora`
+   (e.g. `weknora_<storeprefix>_768` + alias, plus `weknora_<storeprefix>_keywords`).
+3. Run a retrieval query against the bound KB and confirm hits come back.
+4. Copy the KB to another KB and confirm the docs are reindexed
+   (`opensearch.reindex_executed` audit event).
+5. Toggle chunk enabled-status / tag and confirm `_update_by_query` applies it.
+
+## 5. Tear down
+
+```bash
+docker compose -f docker-compose.dev.yml --profile opensearch down -v
+```
+
+## Scope notes
+
+- Large-batch async reindex / delete (task polling) is a follow-up; the sync
+  paths handle typical KB sizes (pagination is bounded by `max_result_window`,
+  default 10000).
+- Native `hybrid` query + search pipeline is out of scope — fusion stays at the
+  service layer (RRF).
diff --git a/frontend/src/api/vector-store.ts b/frontend/src/api/vector-store.ts
index f9aeafe2..dc164c51 100644
--- a/frontend/src/api/vector-store.ts
+++ b/frontend/src/api/vector-store.ts
@@ -29,6 +29,16 @@ export interface FieldSchema {
   sensitive?: boolean
   description?: string
   default?: any
+  // Inclusive bounds for number fields (omitempty on the backend). When
+  // absent the UI falls back to per-field heuristics (isReplicaField).
+  min?: number
+  max?: number
+  // Closed value set for string fields (e.g. knn_engine ∈ lucene|faiss).
+  // When non-empty the UI renders a select instead of a free-text input.
+  enum?: string[]
+  // Marks a field that cannot change after store creation. Informational
+  // for now (edit mode is fully read-only); kept for forward use.
+  immutable?: boolean
 }
 
 // ===== API Functions =====
diff --git a/frontend/src/i18n/locales/en-US.ts b/frontend/src/i18n/locales/en-US.ts
index 80d5669f..67c0d4d5 100755
--- a/frontend/src/i18n/locales/en-US.ts
+++ b/frontend/src/i18n/locales/en-US.ts
@@ -1107,11 +1107,17 @@ export default {
       shards_num: 'Shards',
       replica_number: 'In-memory Replicas',
       desired_shard_count: 'Shard Count',
+      insecure_skip_verify: 'Skip TLS Verification',
+      hnsw_m: 'HNSW M (graph degree)',
+      hnsw_ef_construction: 'HNSW ef_construction',
+      hnsw_ef_search: 'HNSW ef_search',
+      knn_engine: 'k-NN Engine',
     },
     envTag: 'DEFAULT',
     testConnection: 'Test Connection',
     testing: 'Testing...',
     immutableNotice: 'Engine type, connection, and index settings cannot be changed after creation.\nTo change these, delete and recreate.',
+    insecureSkipVerifyWarning: 'Disabling TLS certificate verification exposes the connection to man-in-the-middle attacks. Use only for self-signed development clusters — never in production.',
     validation: {
       nameRequired: 'Name is required',
       engineTypeRequired: 'Engine type is required',
diff --git a/frontend/src/i18n/locales/ko-KR.ts b/frontend/src/i18n/locales/ko-KR.ts
index a24e8651..587faefe 100755
--- a/frontend/src/i18n/locales/ko-KR.ts
+++ b/frontend/src/i18n/locales/ko-KR.ts
@@ -967,11 +967,17 @@ export default {
       shards_num: "샤드 수",
       replica_number: "인메모리 레플리카",
       desired_shard_count: "샤드 수",
+      insecure_skip_verify: "TLS 인증서 검증 생략",
+      hnsw_m: "HNSW M (그래프 차수)",
+      hnsw_ef_construction: "HNSW ef_construction",
+      hnsw_ef_search: "HNSW ef_search",
+      knn_engine: "k-NN 엔진",
     },
     envTag: "DEFAULT",
     testConnection: "연결 테스트",
     testing: "테스트 중...",
     immutableNotice: "엔진 타입, 연결 정보, 인덱스 설정은 생성 후 변경할 수 없습니다.\n변경이 필요하면 삭제 후 다시 생성하세요.",
+    insecureSkipVerifyWarning: "TLS 인증서 검증을 끄면 중간자 공격에 노출됩니다. 자체 서명 인증서를 쓰는 개발 클러스터에서만 사용하고, 운영 환경에서는 절대 사용하지 마세요.",
     validation: {
       nameRequired: "이름은 필수입니다",
       engineTypeRequired: "엔진 타입은 필수입니다",
diff --git a/frontend/src/i18n/locales/ru-RU.ts b/frontend/src/i18n/locales/ru-RU.ts
index 09bb042b..4579c790 100755
--- a/frontend/src/i18n/locales/ru-RU.ts
+++ b/frontend/src/i18n/locales/ru-RU.ts
@@ -1019,11 +1019,17 @@ export default {
       shards_num: 'Шарды',
       replica_number: 'Реплики в памяти',
       desired_shard_count: 'Количество шардов',
+      insecure_skip_verify: 'Пропустить проверку TLS',
+      hnsw_m: 'HNSW M (степень графа)',
+      hnsw_ef_construction: 'HNSW ef_construction',
+      hnsw_ef_search: 'HNSW ef_search',
+      knn_engine: 'Движок k-NN',
     },
     envTag: 'DEFAULT',
     testConnection: 'Тест подключения',
     testing: 'Тестирование...',
     immutableNotice: 'Тип движка, подключение и настройки индекса нельзя изменить после создания.\nДля изменения удалите и создайте заново.',
+    insecureSkipVerifyWarning: 'Отключение проверки сертификата TLS делает соединение уязвимым для атак «человек посередине». Используйте только для dev-кластеров с самоподписанными сертификатами — никогда в продакшене.',
     validation: {
       nameRequired: 'Название обязательно',
       engineTypeRequired: 'Тип движка обязателен',
diff --git a/frontend/src/i18n/locales/zh-CN.ts b/frontend/src/i18n/locales/zh-CN.ts
index 0f0888d0..20009942 100755
--- a/frontend/src/i18n/locales/zh-CN.ts
+++ b/frontend/src/i18n/locales/zh-CN.ts
@@ -965,11 +965,17 @@ export default {
       shards_num: "分片数",
       replica_number: "内存副本数",
       desired_shard_count: "分片数",
+      insecure_skip_verify: "跳过 TLS 证书校验",
+      hnsw_m: "HNSW M（图度数）",
+      hnsw_ef_construction: "HNSW ef_construction",
+      hnsw_ef_search: "HNSW ef_search",
+      knn_engine: "k-NN 引擎",
     },
     envTag: "DEFAULT",
     testConnection: "测试连接",
     testing: "测试中...",
     immutableNotice: "创建后无法更改引擎类型、连接和索引设置。\n如需更改，请删除后重新创建。",
+    insecureSkipVerifyWarning: "关闭 TLS 证书校验会使连接面临中间人攻击风险。仅可用于自签名证书的开发集群，切勿在生产环境使用。",
     validation: {
       nameRequired: "名称为必填项",
       engineTypeRequired: "引擎类型为必填项",
diff --git a/frontend/src/views/settings/VectorStoreSettings.vue b/frontend/src/views/settings/VectorStoreSettings.vue
index 39149fcf..88774ecd 100644
--- a/frontend/src/views/settings/VectorStoreSettings.vue
+++ b/frontend/src/views/settings/VectorStoreSettings.vue
@@ -165,10 +165,15 @@
                 :label="fieldLabel(field.name)"
                 :name="`connection_config.${field.name}`"
               >
-                <t-switch
-                  v-if="field.type === 'boolean'"
-                  v-model="form.connection_config[field.name]"
-                />
+                <div v-if="field.type === 'boolean'" class="boolean-field">
+                  <t-switch v-model="form.connection_config[field.name]" />
+                  <div
+                    v-if="field.name === 'insecure_skip_verify' && form.connection_config[field.name]"
+                    class="field-warning"
+                  >
+                    {{ t('vectorStoreSettings.insecureSkipVerifyWarning') }}
+                  </div>
+                </div>
                 <t-input
                   v-else-if="field.type === 'string' && field.sensitive"
                   v-model="form.connection_config[field.name]"
@@ -201,12 +206,20 @@
               <template v-if="showAdvanced">
                 <template v-for="field in selectedType.index_fields" :key="field.name">
                   <t-form-item :label="fieldLabel(field.name)" :name="`index_config.${field.name}`">
+                    <!-- Closed value set → dropdown (e.g. knn_engine) -->
+                    <t-select
+                      v-if="field.enum && field.enum.length"
+                      v-model="form.index_config[field.name]"
+                      :placeholder="field.default?.toString() || ''"
+                    >
+                      <t-option v-for="opt in field.enum" :key="opt" :value="opt" :label="opt" />
+                    </t-select>
                     <t-input-number
-                      v-if="field.type === 'number'"
+                      v-else-if="field.type === 'number'"
                       v-model="form.index_config[field.name]"
                       :placeholder="field.default?.toString()"
-                      :min="1"
-                      :max="isReplicaField(field.name) ? 10 : 64"
+                      :min="field.min ?? 1"
+                      :max="field.max ?? (isReplicaField(field.name) ? 10 : 64)"
                       theme="normal"
                       style="width: 100%;"
                     />
@@ -861,6 +874,23 @@ onMounted(async () => {
   white-space: pre-line;
 }
 
+/* Wrap switch + warning in a vertical stack so the warning sits on its own
+   line below the switch, independent of TDesign's form-item content flex
+   (which is a nowrap row — margin-top alone has no visible effect there). */
+.boolean-field {
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  width: 100%;
+}
+
+.field-warning {
+  margin-top: 8px;
+  font-size: 12px;
+  line-height: 1.4;
+  color: var(--td-error-color, #d54941);
+}
+
 .readonly-fields {
   padding: 10px 14px;
   background: var(--td-bg-color-secondarycontainer);
diff --git a/internal/application/repository/retriever/opensearch/audit.go b/internal/application/repository/retriever/opensearch/audit.go
new file mode 100644
index 00000000..fa8aca21
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/audit.go
@@ -0,0 +1,50 @@
+package opensearch
+
+import "context"
+
+// AuditSink receives audit events emitted from within the driver at the
+// exact moment they occur (index provisioned, reindex executed). The driver
+// owns this abstraction so it imports no service package — the dependency
+// arrow stays one-way (service implements AuditSink; the driver only invokes
+// it). A nil sink is a no-op, so tests and the env-path (no audit service)
+// need no special casing.
+type AuditSink interface {
+	// EmitIndexCreated fires once when the driver provisions a new k-NN
+	// index. alias is the per-dimension alias (or the keyword-only index
+	// name); dim is the embedding dimension (0 for the keyword-only index).
+	EmitIndexCreated(ctx context.Context, alias string, dim int)
+	// EmitReindexExecuted fires when CopyIndices finishes copying docs from
+	// one index to another.
+	EmitReindexExecuted(ctx context.Context, srcAlias, dstAlias string, docs int64)
+}
+
+// nopSink is the null-object used when no sink is configured, so emit call
+// sites never need a nil check.
+type nopSink struct{}
+
+func (nopSink) EmitIndexCreated(context.Context, string, int)              {}
+func (nopSink) EmitReindexExecuted(context.Context, string, string, int64) {}
+
+var _ AuditSink = nopSink{}
+
+// Option configures a Repository at construction time.
+type Option func(*Repository)
+
+// WithAuditSink injects an audit sink. A nil sink is ignored (the Repository
+// keeps its default no-op behavior).
+func WithAuditSink(s AuditSink) Option {
+	return func(r *Repository) {
+		if s != nil {
+			r.sink = s
+		}
+	}
+}
+
+// auditSink returns the configured sink, or a no-op if none was set (e.g. a
+// Repository built directly in tests, or constructed without WithAuditSink).
+func (r *Repository) auditSink() AuditSink {
+	if r.sink == nil {
+		return nopSink{}
+	}
+	return r.sink
+}
diff --git a/internal/application/repository/retriever/opensearch/audit_config_test.go b/internal/application/repository/retriever/opensearch/audit_config_test.go
new file mode 100644
index 00000000..33cd4263
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/audit_config_test.go
@@ -0,0 +1,153 @@
+package opensearch
+
+import (
+	"context"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/Tencent/WeKnora/internal/types"
+)
+
+// spySink records audit events for assertions.
+type spySink struct {
+	mu           sync.Mutex
+	indexCreated []indexCreatedEvent
+	reindex      []reindexEvent
+}
+
+type indexCreatedEvent struct {
+	alias string
+	dim   int
+}
+type reindexEvent struct {
+	src, dst string
+	docs     int64
+}
+
+func (s *spySink) EmitIndexCreated(_ context.Context, alias string, dim int) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.indexCreated = append(s.indexCreated, indexCreatedEvent{alias, dim})
+}
+
+func (s *spySink) EmitReindexExecuted(_ context.Context, src, dst string, docs int64) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.reindex = append(s.reindex, reindexEvent{src, dst, docs})
+}
+
+// TestBuildInternalCfg_ReadsHNSWFields verifies the HNSW IndexConfig fields
+// flow into internalCfg, falling back to defaults when unset.
+func TestBuildInternalCfg_ReadsHNSWFields(t *testing.T) {
+	t.Run("reads set fields", func(t *testing.T) {
+		cfg, err := buildInternalCfg(&types.IndexConfig{
+			HNSWM:              24,
+			HNSWEFConstruction: 200,
+			HNSWEFSearch:       128,
+			KNNEngine:          "faiss",
+			NumberOfShards:     2,
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if cfg.hnswM != 24 || cfg.hnswEFConstruction != 200 || cfg.efSearch != 128 || cfg.knnEngine != "faiss" {
+			t.Errorf("HNSW not wired: %+v", cfg)
+		}
+		if cfg.shards != 2 {
+			t.Errorf("shards: want 2, got %d", cfg.shards)
+		}
+	})
+
+	t.Run("defaults when unset", func(t *testing.T) {
+		cfg, err := buildInternalCfg(&types.IndexConfig{})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if cfg.hnswM != 16 || cfg.hnswEFConstruction != 100 || cfg.efSearch != 100 || cfg.knnEngine != "lucene" {
+			t.Errorf("defaults not applied: %+v", cfg)
+		}
+	})
+
+	t.Run("nil config is all defaults", func(t *testing.T) {
+		cfg, err := buildInternalCfg(nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if cfg.knnEngine != "lucene" || cfg.hnswM != 16 {
+			t.Errorf("nil defaults wrong: %+v", cfg)
+		}
+	})
+}
+
+// TestBuildIndexMapping_ReflectsHNSWConfig verifies the end-to-end path
+// IndexConfig → buildInternalCfg → buildIndexMapping carries the operator's
+// HNSW values into the cluster mapping JSON (regression guard for the wire-
+// through, since defaults coincide with common values).
+func TestBuildIndexMapping_ReflectsHNSWConfig(t *testing.T) {
+	cfg, err := buildInternalCfg(&types.IndexConfig{
+		HNSWM:              24,
+		HNSWEFConstruction: 200,
+		HNSWEFSearch:       128,
+		KNNEngine:          "faiss",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	body, err := buildIndexMapping(cfg, 768)
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := string(body)
+	for _, want := range []string{`"m":24`, `"ef_construction":200`, `"engine":"faiss"`, `"knn.algo_param.ef_search":128`} {
+		if !strings.Contains(s, want) {
+			t.Errorf("mapping JSON missing %q\n%s", want, s)
+		}
+	}
+}
+
+// TestWithAuditSink_SetsAndNilSafe verifies the functional option.
+func TestWithAuditSink_SetsAndNilSafe(t *testing.T) {
+	spy := &spySink{}
+	r := &Repository{}
+	WithAuditSink(spy)(r)
+	if r.sink != spy {
+		t.Fatal("WithAuditSink did not set the sink")
+	}
+	// nil must not clobber an already-set sink
+	WithAuditSink(nil)(r)
+	if r.sink != spy {
+		t.Fatal("WithAuditSink(nil) clobbered the sink")
+	}
+}
+
+// TestAuditSink_NopByDefault verifies a Repository with no sink does not panic
+// when the audit accessor is used (nopSink fallback).
+func TestAuditSink_NopByDefault(t *testing.T) {
+	var _ AuditSink = nopSink{} // compile-time assertion
+	r := &Repository{}          // sink left nil
+	// Must not panic.
+	r.auditSink().EmitIndexCreated(context.Background(), "weknora_768", 768)
+	r.auditSink().EmitReindexExecuted(context.Background(), "a", "b", 3)
+}
+
+// TestAuditSink_EmitIndexCreated_OnEnsureReady verifies createIndexAndAlias
+// emits exactly one index-created event with the per-dim alias when a new
+// index is provisioned.
+func TestAuditSink_EmitIndexCreated_OnEnsureReady(t *testing.T) {
+	repo, ts := newTestRepo(t, (&indexLifecycleHandler{}).ServeHTTP)
+	defer ts.Close()
+	spy := &spySink{}
+	repo.sink = spy
+
+	if err := repo.ensureReady(context.Background(), 768); err != nil {
+		t.Fatalf("ensureReady: %v", err)
+	}
+	if len(spy.indexCreated) != 1 {
+		t.Fatalf("want 1 index_created event, got %d", len(spy.indexCreated))
+	}
+	got := spy.indexCreated[0]
+	if got.alias != "weknora_test_768" || got.dim != 768 {
+		t.Errorf("event mismatch: %+v", got)
+	}
+}
diff --git a/internal/application/repository/retriever/opensearch/bulk_update.go b/internal/application/repository/retriever/opensearch/bulk_update.go
new file mode 100644
index 00000000..97e64caf
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/bulk_update.go
@@ -0,0 +1,107 @@
+package opensearch
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"sort"
+
+	osapi "github.com/opensearch-project/opensearch-go/v4/opensearchapi"
+)
+
+// BatchUpdateChunkEnabledStatus flips is_enabled for the given chunks. The
+// status map is grouped by value into one _update_by_query per distinct value
+// (mirrors the Qdrant grouping pattern), so the request body carries the
+// chunk ids via a terms filter and the new value via bound script params —
+// never per-chunk string interpolation.
+//
+// Targets the cross-dim <base>_* pattern: a chunk's embedding dimension is
+// not known here, and the same chunk_id is unique across the store's dim
+// indices + the keyword-only index.
+func (r *Repository) BatchUpdateChunkEnabledStatus(ctx context.Context, chunkStatusMap map[string]bool) error {
+	if len(chunkStatusMap) == 0 {
+		return nil
+	}
+	groups := map[bool][]string{}
+	for id, v := range chunkStatusMap {
+		groups[v] = append(groups[v], id)
+	}
+	// Deterministic order (false then true) for predictable behavior/tests.
+	for _, v := range []bool{false, true} {
+		ids := groups[v]
+		if len(ids) == 0 {
+			continue
+		}
+		sort.Strings(ids)
+		if err := r.updateByQueryScript(ctx, ids,
+			"ctx._source.is_enabled = params.v", map[string]any{"v": v}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// BatchUpdateChunkTagID sets tag_id for the given chunks, grouped by tag.
+func (r *Repository) BatchUpdateChunkTagID(ctx context.Context, chunkTagMap map[string]string) error {
+	if len(chunkTagMap) == 0 {
+		return nil
+	}
+	groups := map[string][]string{}
+	for id, tag := range chunkTagMap {
+		groups[tag] = append(groups[tag], id)
+	}
+	tags := make([]string, 0, len(groups))
+	for tag := range groups {
+		tags = append(tags, tag)
+	}
+	sort.Strings(tags)
+	for _, tag := range tags {
+		ids := groups[tag]
+		sort.Strings(ids)
+		if err := r.updateByQueryScript(ctx, ids,
+			"ctx._source.tag_id = params.v", map[string]any{"v": tag}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// updateByQueryScript runs an _update_by_query over the cross-dim <base>_*
+// pattern, matching the given chunk ids via a terms filter and applying a
+// constant Painless source with caller values flowing only through bound
+// params (Painless-injection-safe).
+func (r *Repository) updateByQueryScript(
+	ctx context.Context, chunkIDs []string, source string, params map[string]any,
+) error {
+	body, err := json.Marshal(map[string]any{
+		"query": map[string]any{
+			"terms": map[string]any{"chunk_id": chunkIDs},
+		},
+		"script": map[string]any{
+			"lang":   "painless",
+			"source": source,
+			"params": params,
+		},
+	})
+	if err != nil {
+		return fmt.Errorf("opensearch: marshal update_by_query body: %w", err)
+	}
+	// Q2: UpdateByQueryParams.Refresh is *bool — the wire value "wait_for" is
+	// not expressible via the typed SDK, so we force an immediate refresh.
+	refresh := true
+	resp, err := r.client.UpdateByQuery(ctx, osapi.UpdateByQueryReq{
+		Indices: []string{r.baseIndex + "_*"},
+		Body:    bytes.NewReader(body),
+		Params:  osapi.UpdateByQueryParams{Refresh: &refresh},
+	})
+	if err != nil {
+		return wrapTransport(err)
+	}
+	if resp == nil {
+		return nil
+	}
+	defer drainAndClose(resp.Inspect().Response.Body)
+	return inspectByQueryResponse(io.LimitReader(resp.Inspect().Response.Body, 16<<20))
+}
diff --git a/internal/application/repository/retriever/opensearch/byquery.go b/internal/application/repository/retriever/opensearch/byquery.go
new file mode 100644
index 00000000..912fcaac
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/byquery.go
@@ -0,0 +1,51 @@
+package opensearch
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/Tencent/WeKnora/internal/logger"
+)
+
+// inspectByQueryResponse parses an _update_by_query / _delete_by_query
+// response and surfaces partial failures without leaking cluster-side reason
+// strings (which may embed document content). Mirrors inspectBulkResponse:
+// the full reason goes to the debug log only; the returned error carries the
+// bounded id + type. A non-zero version_conflicts count with no hard failures
+// is logged as a warning but not treated as an error.
+func inspectByQueryResponse(body io.Reader) error {
+	var r struct {
+		VersionConflicts int `json:"version_conflicts"`
+		Failures         []struct {
+			ID    string `json:"id"`
+			Cause struct {
+				Type   string `json:"type"`
+				Reason string `json:"reason"`
+			} `json:"cause"`
+		} `json:"failures"`
+	}
+	if err := json.NewDecoder(body).Decode(&r); err != nil {
+		return fmt.Errorf("opensearch: parse by-query response: %w", ErrTransport)
+	}
+	log := logger.GetLogger(context.Background())
+	if len(r.Failures) == 0 {
+		if r.VersionConflicts > 0 {
+			log.Warnf("[OpenSearch] by-query had %d version conflicts (proceeded)", r.VersionConflicts)
+		}
+		return nil
+	}
+	var msgs []string
+	for _, f := range r.Failures {
+		// Full reason → debug log only (may contain document content).
+		log.Debugf("[OpenSearch] by-query failure: id=%s type=%s reason=%s",
+			f.ID, f.Cause.Type, f.Cause.Reason)
+		if len(msgs) < 5 {
+			msgs = append(msgs, fmt.Sprintf("[%s] %s", f.ID, f.Cause.Type))
+		}
+	}
+	return fmt.Errorf("opensearch: by-query partial failure (%d failed, first 5: %s): %w",
+		len(r.Failures), strings.Join(msgs, "; "), ErrTransport)
+}
diff --git a/internal/application/repository/retriever/opensearch/config.go b/internal/application/repository/retriever/opensearch/config.go
index 90b8f9b1..0c636e82 100644
--- a/internal/application/repository/retriever/opensearch/config.go
+++ b/internal/application/repository/retriever/opensearch/config.go
@@ -15,16 +15,15 @@ type internalCfg struct {
 }
 
 // buildInternalCfg projects IndexConfig to the driver-internal view,
-// substituting defaults for unset fields. Validation of value ranges
-// (e.g. hnsw_m / ef_construction caps) is a service-layer concern handled
-// elsewhere; this function applies defaults only and never rejects.
+// substituting defaults for unset (zero / empty) fields. Validation of value
+// ranges (e.g. hnsw_m / ef_construction caps) is a service-layer concern
+// handled elsewhere (validateOpenSearchIndexConfig at CreateStore); this
+// function applies defaults only and never rejects. The env-path bypasses
+// service validation entirely, so the defaults below are its safety net.
 //
-// OpenSearch-specific overrides (knn_engine, hnsw_m, hnsw_ef_construction,
-// hnsw_ef_search) are intentionally NOT read from IndexConfig here:
-// IndexConfig is a schema shared across all drivers, and adding OpenSearch-
-// specific fields would surface them in the shared VectorStoreFieldInfo
-// form visible to every driver's create UI. Wiring those fields through to
-// IndexConfig is a follow-up that lands alongside the activation switch.
+// The OpenSearch-specific HNSW fields (knn_engine, hnsw_m,
+// hnsw_ef_construction, hnsw_ef_search) are read here. They are omitempty on
+// IndexConfig, so they do not affect other drivers' serialized config.
 func buildInternalCfg(c *types.IndexConfig) (internalCfg, error) {
 	cfg := internalCfg{
 		shards:             4,        // matches the keyword-index default upstream
@@ -43,5 +42,17 @@ func buildInternalCfg(c *types.IndexConfig) (internalCfg, error) {
 	if c.NumberOfReplicas > 0 {
 		cfg.replicas = c.NumberOfReplicas
 	}
+	if c.KNNEngine != "" {
+		cfg.knnEngine = c.KNNEngine
+	}
+	if c.HNSWM > 0 {
+		cfg.hnswM = c.HNSWM
+	}
+	if c.HNSWEFConstruction > 0 {
+		cfg.hnswEFConstruction = c.HNSWEFConstruction
+	}
+	if c.HNSWEFSearch > 0 {
+		cfg.efSearch = c.HNSWEFSearch
+	}
 	return cfg, nil
 }
diff --git a/internal/application/repository/retriever/opensearch/copy.go b/internal/application/repository/retriever/opensearch/copy.go
new file mode 100644
index 00000000..7cbda73f
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/copy.go
@@ -0,0 +1,194 @@
+package opensearch
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/google/uuid"
+	osapi "github.com/opensearch-project/opensearch-go/v4/opensearchapi"
+
+	"github.com/Tencent/WeKnora/internal/logger"
+	"github.com/Tencent/WeKnora/internal/types"
+)
+
+// copyBatchSize is the pagination size for the source scan. Kept under the
+// BatchSave per-call cap so each copied page is a single bulk request.
+const copyBatchSize = 500
+
+// copySourceDoc is the full _source read during CopyIndices — it includes the
+// embedding vector and is_recommended, which the retrieve-path hit struct
+// omits because retrieval does not need them.
+type copySourceDoc struct {
+	Content         string    `json:"content"`
+	SourceID        string    `json:"source_id"`
+	SourceType      int       `json:"source_type"`
+	ChunkID         string    `json:"chunk_id"`
+	KnowledgeID     string    `json:"knowledge_id"`
+	KnowledgeBaseID string    `json:"knowledge_base_id"`
+	TagID           string    `json:"tag_id"`
+	IsEnabled       bool      `json:"is_enabled"`
+	IsRecommended   bool      `json:"is_recommended"`
+	Embedding       []float32 `json:"embedding"`
+}
+
+// transformSourceID mirrors the sibling drivers' source_id remap:
+//   - regular chunk (source_id == chunk_id) → target chunk id
+//   - generated question (source_id == "<chunk>-<q>") → "<targetChunk>-<q>"
+//   - anything else → a fresh uuid
+func transformSourceID(sourceID, chunkID, targetChunkID string) string {
+	switch {
+	case sourceID == chunkID:
+		return targetChunkID
+	case strings.HasPrefix(sourceID, chunkID+"-"):
+		return targetChunkID + "-" + strings.TrimPrefix(sourceID, chunkID+"-")
+	default:
+		return uuid.New().String()
+	}
+}
+
+// CopyIndices copies all docs of one knowledge base into another (within the
+// same store) by scanning the source and re-saving via BatchSave — mirroring
+// the Elasticsearch / Qdrant drivers (search→BatchSave), which yields the
+// source_id transformation and dim/keyword routing for free. Runs
+// synchronously and paginates; the large-batch background-task path is a
+// later change.
+//
+// NOTE: from/size pagination is bounded by the index's max_result_window
+// (default 10000). Copies larger than that require the scroll-based async
+// path (a later change).
+func (r *Repository) CopyIndices(
+	ctx context.Context,
+	sourceKnowledgeBaseID string,
+	sourceToTargetKBIDMap map[string]string, // keyed by source knowledge_id (mirrors sibling drivers)
+	sourceToTargetChunkIDMap map[string]string,
+	targetKnowledgeBaseID string,
+	dimension int,
+	knowledgeType string,
+) error {
+	log := logger.GetLogger(ctx)
+	if len(sourceToTargetChunkIDMap) == 0 {
+		log.Warn("[OpenSearch] CopyIndices: empty chunk mapping, skipping")
+		return nil
+	}
+	if dimension <= 0 {
+		return fmt.Errorf("opensearch: CopyIndices requires dim > 0, got %d: %w",
+			dimension, ErrDimensionMismatch)
+	}
+	if err := r.ensureReady(ctx, dimension); err != nil {
+		return err
+	}
+	alias := r.indexAlias(dimension)
+
+	var total int64
+	for from := 0; ; from += copyBatchSize {
+		docs, err := r.copyScanBatch(ctx, alias, sourceKnowledgeBaseID, from, copyBatchSize)
+		if err != nil {
+			return err
+		}
+		if len(docs) == 0 {
+			break
+		}
+		infos := make([]*types.IndexInfo, 0, len(docs))
+		embMap := make(map[string][]float32, len(docs))
+		enabledMap := make(map[string]bool, len(docs))
+		for i := range docs {
+			d := &docs[i]
+			targetChunkID, ok := sourceToTargetChunkIDMap[d.ChunkID]
+			if !ok {
+				log.Warnf("[OpenSearch] CopyIndices: source chunk %s not mapped, skipping", d.ChunkID)
+				continue
+			}
+			targetKnowledgeID, ok := sourceToTargetKBIDMap[d.KnowledgeID]
+			if !ok {
+				log.Warnf("[OpenSearch] CopyIndices: source knowledge %s not mapped, skipping", d.KnowledgeID)
+				continue
+			}
+			targetSourceID := transformSourceID(d.SourceID, d.ChunkID, targetChunkID)
+			if len(d.Embedding) > 0 {
+				// BatchSave looks up embeddings by SourceID (lookupEmbedding),
+				// so key by the target source id — not the chunk id, which is
+				// the Elasticsearch driver's convention.
+				embMap[targetSourceID] = d.Embedding
+			}
+			enabledMap[targetChunkID] = d.IsEnabled
+			infos = append(infos, &types.IndexInfo{
+				Content:         d.Content,
+				SourceID:        targetSourceID,
+				SourceType:      types.SourceType(d.SourceType),
+				ChunkID:         targetChunkID,
+				KnowledgeID:     targetKnowledgeID,
+				KnowledgeBaseID: targetKnowledgeBaseID,
+				KnowledgeType:   knowledgeType,
+				TagID:           d.TagID,
+				IsEnabled:       d.IsEnabled,
+				IsRecommended:   d.IsRecommended,
+			})
+		}
+		if len(infos) > 0 {
+			params := map[string]any{
+				"embedding":     embMap,
+				"chunk_enabled": enabledMap,
+			}
+			if err := r.BatchSave(ctx, infos, params); err != nil {
+				return fmt.Errorf("opensearch: CopyIndices batch save: %w", err)
+			}
+			total += int64(len(infos))
+		}
+		if len(docs) < copyBatchSize {
+			break
+		}
+	}
+	log.Infof("[OpenSearch] CopyIndices: copied %d docs (KB %s → %s, dim=%d)",
+		total, sourceKnowledgeBaseID, targetKnowledgeBaseID, dimension)
+	r.auditSink().EmitReindexExecuted(ctx, alias, alias, total)
+	return nil
+}
+
+// copyScanBatch reads one page of docs belonging to sourceKB from the per-dim
+// index, decoding the full _source (including the embedding vector).
+func (r *Repository) copyScanBatch(
+	ctx context.Context, index, sourceKB string, from, size int,
+) ([]copySourceDoc, error) {
+	body, err := json.Marshal(map[string]any{
+		"from": from,
+		"size": size,
+		"query": map[string]any{
+			"bool": map[string]any{
+				"filter": []any{
+					map[string]any{"term": map[string]any{"knowledge_base_id": sourceKB}},
+				},
+			},
+		},
+	})
+	if err != nil {
+		return nil, fmt.Errorf("opensearch: marshal copy scan body: %w", err)
+	}
+	req := osapi.SearchReq{Indices: []string{index}, Body: bytes.NewReader(body)}
+	resp, err := r.client.Search(ctx, &req)
+	if err != nil {
+		if isNotFound(err) {
+			return nil, fmt.Errorf("opensearch: index %s missing: %w", index, ErrIndexNotFound)
+		}
+		return nil, wrapTransport(err)
+	}
+	defer drainAndClose(resp.Inspect().Response.Body)
+	var parsed struct {
+		Hits struct {
+			Hits []struct {
+				Source copySourceDoc `json:"_source"`
+			} `json:"hits"`
+		} `json:"hits"`
+	}
+	if err := json.NewDecoder(io.LimitReader(resp.Inspect().Response.Body, 64<<20)).Decode(&parsed); err != nil {
+		return nil, fmt.Errorf("opensearch: parse copy scan response: %w", ErrTransport)
+	}
+	out := make([]copySourceDoc, len(parsed.Hits.Hits))
+	for i, h := range parsed.Hits.Hits {
+		out[i] = h.Source
+	}
+	return out, nil
+}
diff --git a/internal/application/repository/retriever/opensearch/copy_bulk_test.go b/internal/application/repository/retriever/opensearch/copy_bulk_test.go
new file mode 100644
index 00000000..185c8f5e
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/copy_bulk_test.go
@@ -0,0 +1,193 @@
+package opensearch
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"strings"
+	"sync"
+	"testing"
+)
+
+// TestTransformSourceID covers the generated-question / regular / fallback
+// branches that CopyIndices uses to remap source_id.
+func TestTransformSourceID(t *testing.T) {
+	t.Run("regular chunk uses target chunk id", func(t *testing.T) {
+		if got := transformSourceID("chunk1", "chunk1", "tgt1"); got != "tgt1" {
+			t.Errorf("want tgt1, got %s", got)
+		}
+	})
+	t.Run("generated question preserves question id", func(t *testing.T) {
+		if got := transformSourceID("chunk1-q7", "chunk1", "tgt1"); got != "tgt1-q7" {
+			t.Errorf("want tgt1-q7, got %s", got)
+		}
+	})
+	t.Run("unrelated source id gets fresh uuid", func(t *testing.T) {
+		got := transformSourceID("totally-different", "chunk1", "tgt1")
+		if got == "totally-different" || got == "tgt1" || len(got) != 36 {
+			t.Errorf("want fresh uuid, got %q", got)
+		}
+	})
+}
+
+// TestCopyIndices_EmptyMapping_NoOp verifies an empty chunk map short-circuits
+// before any HTTP call.
+func TestCopyIndices_EmptyMapping_NoOp(t *testing.T) {
+	repo, ts := newTestRepo(t, func(w http.ResponseWriter, r *http.Request) {
+		t.Errorf("unexpected HTTP call: %s %s", r.Method, r.URL.Path)
+	})
+	defer ts.Close()
+	err := repo.CopyIndices(context.Background(), "kbSrc", map[string]string{}, map[string]string{}, "kbDst", 768, "manual")
+	if err != nil {
+		t.Fatalf("want nil, got %v", err)
+	}
+}
+
+// TestCopyIndices_ScanThenBatchSave verifies the search→BatchSave path:
+// remaps IDs, keys the embedding by the *target source id* (OpenSearch
+// BatchSave's lookup key), and emits one reindex audit event.
+func TestCopyIndices_ScanThenBatchSave(t *testing.T) {
+	var (
+		mu        sync.Mutex
+		bulkBody  string
+		searchCnt int
+	)
+	handler := func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case r.Method == http.MethodHead:
+			w.WriteHeader(http.StatusOK) // alias exists → ensureReady no-op
+		case strings.Contains(r.URL.Path, "_search"):
+			mu.Lock()
+			searchCnt++
+			first := searchCnt == 1
+			mu.Unlock()
+			if first {
+				_, _ = w.Write([]byte(`{"hits":{"hits":[
+					{"_source":{"content":"c","source_id":"srcChunk","source_type":1,"chunk_id":"srcChunk","knowledge_id":"srcKnow","knowledge_base_id":"kbSrc","tag_id":"t","is_enabled":true,"is_recommended":false,"embedding":[0.1,0.2,0.3]}}
+				]}}`))
+			} else {
+				_, _ = w.Write([]byte(`{"hits":{"hits":[]}}`))
+			}
+		case strings.HasSuffix(r.URL.Path, "/_bulk"):
+			b, _ := io.ReadAll(r.Body)
+			mu.Lock()
+			bulkBody = string(b)
+			mu.Unlock()
+			_, _ = w.Write([]byte(`{"errors":false,"items":[]}`))
+		default:
+			_, _ = w.Write([]byte(`{}`))
+		}
+	}
+	repo, ts := newTestRepo(t, handler)
+	defer ts.Close()
+	spy := &spySink{}
+	repo.sink = spy
+
+	err := repo.CopyIndices(context.Background(), "kbSrc",
+		map[string]string{"srcKnow": "tgtKnow"}, // knowledge_id remap (sourceToTargetKBIDMap is keyed by knowledge_id, mirroring ES)
+		map[string]string{"srcChunk": "tgtChunk"},
+		"kbDst", 768, "manual")
+	if err != nil {
+		t.Fatalf("CopyIndices: %v", err)
+	}
+
+	mu.Lock()
+	defer mu.Unlock()
+	if bulkBody == "" {
+		t.Fatal("no bulk request captured")
+	}
+	// Target IDs present, source IDs gone from the written doc.
+	for _, want := range []string{`"chunk_id":"tgtChunk"`, `"knowledge_id":"tgtKnow"`, `"knowledge_base_id":"kbDst"`, `"source_id":"tgtChunk"`} {
+		if !strings.Contains(bulkBody, want) {
+			t.Errorf("bulk body missing %q\n%s", want, bulkBody)
+		}
+	}
+	if strings.Contains(bulkBody, `"knowledge_base_id":"kbSrc"`) {
+		t.Errorf("bulk body leaked source KB id\n%s", bulkBody)
+	}
+	// Embedding written (keyed by target source id internally).
+	if !strings.Contains(bulkBody, "0.1") {
+		t.Errorf("embedding not written\n%s", bulkBody)
+	}
+	if len(spy.reindex) != 1 || spy.reindex[0].docs != 1 {
+		t.Errorf("want 1 reindex event with docs=1, got %+v", spy.reindex)
+	}
+}
+
+// TestBatchUpdateChunkEnabledStatus_GroupedUpdateByQuery verifies the status
+// map is grouped by value into one _update_by_query per distinct value, each
+// passing chunk ids via terms + the new value via bound script params.
+func TestBatchUpdateChunkEnabledStatus_GroupedUpdateByQuery(t *testing.T) {
+	var (
+		mu     sync.Mutex
+		bodies []string
+	)
+	handler := func(w http.ResponseWriter, r *http.Request) {
+		if strings.Contains(r.URL.Path, "_update_by_query") {
+			b, _ := io.ReadAll(r.Body)
+			mu.Lock()
+			bodies = append(bodies, string(b))
+			mu.Unlock()
+			_, _ = w.Write([]byte(`{"updated":1,"version_conflicts":0,"failures":[]}`))
+			return
+		}
+		_, _ = w.Write([]byte(`{}`))
+	}
+	repo, ts := newTestRepo(t, handler)
+	defer ts.Close()
+
+	err := repo.BatchUpdateChunkEnabledStatus(context.Background(), map[string]bool{
+		"c1": true, "c2": false, "c3": true,
+	})
+	if err != nil {
+		t.Fatalf("BatchUpdateChunkEnabledStatus: %v", err)
+	}
+
+	mu.Lock()
+	defer mu.Unlock()
+	if len(bodies) != 2 {
+		t.Fatalf("want 2 grouped update_by_query calls (true/false), got %d: %v", len(bodies), bodies)
+	}
+	joined := strings.Join(bodies, "\n")
+	for _, want := range []string{"c1", "c2", "c3", "is_enabled", "params"} {
+		if !strings.Contains(joined, want) {
+			t.Errorf("update_by_query bodies missing %q\n%s", want, joined)
+		}
+	}
+}
+
+func TestBatchUpdateChunkEnabledStatus_Empty_NoOp(t *testing.T) {
+	repo, ts := newTestRepo(t, func(w http.ResponseWriter, r *http.Request) {
+		t.Errorf("unexpected HTTP call: %s %s", r.Method, r.URL.Path)
+	})
+	defer ts.Close()
+	if err := repo.BatchUpdateChunkEnabledStatus(context.Background(), map[string]bool{}); err != nil {
+		t.Fatalf("want nil, got %v", err)
+	}
+}
+
+// TestInspectByQueryResponse covers the success path and the failure path,
+// asserting cluster-side reason text is NOT surfaced in the returned error.
+func TestInspectByQueryResponse(t *testing.T) {
+	t.Run("clean response", func(t *testing.T) {
+		body := strings.NewReader(`{"updated":5,"version_conflicts":0,"failures":[]}`)
+		if err := inspectByQueryResponse(body); err != nil {
+			t.Fatalf("want nil, got %v", err)
+		}
+	})
+	t.Run("failures do not leak reason", func(t *testing.T) {
+		body := strings.NewReader(`{"updated":1,"version_conflicts":0,"failures":[
+			{"id":"c9","cause":{"type":"version_conflict_engine_exception","reason":"SECRET document body leaked here"}}
+		]}`)
+		err := inspectByQueryResponse(body)
+		if err == nil {
+			t.Fatal("want error for failures, got nil")
+		}
+		if strings.Contains(err.Error(), "SECRET") {
+			t.Errorf("error leaked cluster reason: %v", err)
+		}
+		if !strings.Contains(err.Error(), "version_conflict_engine_exception") {
+			t.Errorf("error should surface bounded type: %v", err)
+		}
+	})
+}
diff --git a/internal/application/repository/retriever/opensearch/healthcheck.go b/internal/application/repository/retriever/opensearch/healthcheck.go
new file mode 100644
index 00000000..af6700d8
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/healthcheck.go
@@ -0,0 +1,23 @@
+package opensearch
+
+import (
+	"context"
+
+	"github.com/Tencent/WeKnora/internal/types"
+)
+
+// TestConnection verifies an OpenSearch cluster is reachable, runs a
+// supported version, and has the k-NN plugin installed on every node. It is
+// the connectivity probe used by the VectorStore service's CreateStore
+// health-check (the driver's unexported probes are reused here). Returns a
+// wrapped sentinel error on failure; nil on success.
+func TestConnection(ctx context.Context, cfg *types.ConnectionConfig) error {
+	client, err := NewOpenSearchClient(cfg)
+	if err != nil {
+		return err
+	}
+	if err := probeVersion(ctx, client); err != nil {
+		return err
+	}
+	return probeKNNPlugin(ctx, client)
+}
diff --git a/internal/application/repository/retriever/opensearch/healthcheck_test.go b/internal/application/repository/retriever/opensearch/healthcheck_test.go
new file mode 100644
index 00000000..55ca032d
--- /dev/null
+++ b/internal/application/repository/retriever/opensearch/healthcheck_test.go
@@ -0,0 +1,50 @@
+package opensearch
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	osapi "github.com/opensearch-project/opensearch-go/v4/opensearchapi"
+
+	"github.com/Tencent/WeKnora/internal/types"
+)
+
+// clusterHandler serves both GET / (version info) and /_cat/plugins, so the
+// full TestConnection probe (version + k-NN plugin) can run end to end.
+func clusterHandler(distribution, number string, plugins []osapi.CatPluginResp) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		if r.URL.Path == "/_cat/plugins" {
+			_ = json.NewEncoder(w).Encode(plugins)
+			return
+		}
+		_, _ = w.Write([]byte(`{"version":{"distribution":"` + distribution + `","number":"` + number + `"}}`))
+	}
+}
+
+func TestTestConnection_Success(t *testing.T) {
+	ts := httptest.NewServer(clusterHandler("opensearch", "3.3.2", []osapi.CatPluginResp{
+		{Name: "node-1", Component: "opensearch-knn"},
+	}))
+	defer ts.Close()
+	if err := TestConnection(context.Background(), &types.ConnectionConfig{Addr: ts.URL}); err != nil {
+		t.Errorf("healthy cluster: want nil, got %v", err)
+	}
+}
+
+func TestTestConnection_RejectsElasticsearch(t *testing.T) {
+	ts := httptest.NewServer(clusterHandler("elasticsearch", "8.10.4", nil))
+	defer ts.Close()
+	if err := TestConnection(context.Background(), &types.ConnectionConfig{Addr: ts.URL}); err == nil {
+		t.Error("elasticsearch cluster should be rejected")
+	}
+}
+
+func TestTestConnection_EmptyAddr(t *testing.T) {
+	if err := TestConnection(context.Background(), &types.ConnectionConfig{}); err == nil {
+		t.Error("empty addr should be rejected")
+	}
+}
diff --git a/internal/application/repository/retriever/opensearch/mapping.go b/internal/application/repository/retriever/opensearch/mapping.go
index 451d98ca..ca3b2ad9 100644
--- a/internal/application/repository/retriever/opensearch/mapping.go
+++ b/internal/application/repository/retriever/opensearch/mapping.go
@@ -77,6 +77,11 @@ func (r *Repository) createIndexAndAlias(ctx context.Context, dim int) error {
 		}
 		return fmt.Errorf("put alias %s → %s: %w", alias, realIndex, err)
 	}
+	if indexCreated {
+		// Emit only when we actually provisioned the index (not when a
+		// concurrent writer / existing index short-circuited above).
+		r.auditSink().EmitIndexCreated(ctx, alias, dim)
+	}
 	return nil
 }
 
@@ -217,6 +222,7 @@ func (r *Repository) ensureKeywordsIndex(ctx context.Context) error {
 		r.keywordsErr = err
 		return err
 	}
+	created := false
 	if err := r.indicesCreate(ctx, name, body); err != nil {
 		if !isAlreadyExistsError(err) {
 			r.keywordsErr = err
@@ -224,9 +230,15 @@ func (r *Repository) ensureKeywordsIndex(ctx context.Context) error {
 		}
 		// resource_already_exists_exception — race with concurrent process,
 		// treat as success.
+	} else {
+		created = true
 	}
 	r.keywordsReady = true
 	r.keywordsErr = nil
+	if created {
+		// dim=0 marks the dim-less keyword-only index.
+		r.auditSink().EmitIndexCreated(ctx, name, 0)
+	}
 	return nil
 }
 
diff --git a/internal/application/repository/retriever/opensearch/repository.go b/internal/application/repository/retriever/opensearch/repository.go
index fee20f9a..8ffe7a73 100644
--- a/internal/application/repository/retriever/opensearch/repository.go
+++ b/internal/application/repository/retriever/opensearch/repository.go
@@ -64,6 +64,11 @@ type Repository struct {
 	keywordsMu    sync.Mutex
 	keywordsReady bool
 	keywordsErr   error
+
+	// sink receives audit events (index created / reindex executed). nil
+	// means no auditing; use r.auditSink() to get a non-nil sink. Set via
+	// WithAuditSink at construction.
+	sink AuditSink
 }
 
 // Compile-time interface satisfaction (Go best practice — keeps the build
@@ -87,6 +92,10 @@ var _ interfaces.RetrieveEngineRepository = (*Repository)(nil)
 // indexCfg is optional — pass nil to use env var (OPENSEARCH_INDEX) or
 // default ("weknora") values.
 //
+// Optional behavior is configured via functional options (e.g.
+// WithAuditSink). Passing no options keeps audit emission as a no-op, so the
+// env-path and tests need no extra wiring.
+//
 // Returns a typed sentinel error wrapped with %w; callers translate to
 // AppError at the engine-factory boundary.
 func NewRepository(
@@ -94,6 +103,7 @@ func NewRepository(
 	client *osapi.Client,
 	storeID string,
 	indexCfg *types.IndexConfig,
+	opts ...Option,
 ) (interfaces.RetrieveEngineRepository, error) {
 	log := logger.GetLogger(ctx)
 
@@ -135,6 +145,9 @@ func NewRepository(
 		once:      make(map[int]*sync.Once),
 		initErr:   make(map[int]error),
 	}
+	for _, opt := range opts {
+		opt(r)
+	}
 	log.Infof("[OpenSearch] repository ready (baseIndex=%s, knn_engine=%s, hnsw_m=%d)",
 		base, icfg.knnEngine, icfg.hnswM)
 	return r, nil
diff --git a/internal/application/repository/retriever/opensearch/repository_test.go b/internal/application/repository/retriever/opensearch/repository_test.go
index 76bf83c6..687f0cd4 100644
--- a/internal/application/repository/retriever/opensearch/repository_test.go
+++ b/internal/application/repository/retriever/opensearch/repository_test.go
@@ -218,18 +218,18 @@ func TestSanitizeIndexName_RejectsInvalid(t *testing.T) {
 func TestParseMajorMinor(t *testing.T) {
 	t.Parallel()
 	cases := []struct {
-		in         string
-		wantMaj    int
-		wantMinor  int
+		in        string
+		wantMaj   int
+		wantMinor int
 	}{
 		{"3.3.2", 3, 3},
 		{"2.10.0", 2, 10},
-		{"2.10", 2, 10},  // missing patch — must still parse
+		{"2.10", 2, 10}, // missing patch — must still parse
 		{"3.0.0-rc1", 3, 0},
 		{"2.10.0-SNAPSHOT", 2, 10},
 		{"1.3.18", 1, 3},
-		{"abc", 0, 0},  // unparseable
-		{"3", 0, 0},    // missing minor
+		{"abc", 0, 0}, // unparseable
+		{"3", 0, 0},   // missing minor
 		{"", 0, 0},
 	}
 	for _, tc := range cases {
@@ -636,9 +636,9 @@ func TestEffectiveTopK(t *testing.T) {
 		in   int
 		want int
 	}{
-		{0, 10},     // default
-		{-5, 10},    // negative falls back to default
-		{5, 5},      // normal
+		{0, 10},  // default
+		{-5, 10}, // negative falls back to default
+		{5, 5},   // normal
 		{10000, 10000},
 		{50000, 10000}, // cap
 	}
@@ -992,7 +992,7 @@ func TestEnsureReady_PerDimensionIsolation(t *testing.T) {
 // errorHandler returns a configurable status code for index PUTs to
 // simulate transient (5xx) vs permanent (400) failures.
 type errorHandler struct {
-	statusForIndexPut int
+	statusForIndexPut  int
 	indexPutsAttempted atomic.Int32
 }
 
@@ -1123,34 +1123,14 @@ func TestNewRepository_AcceptsLongStoreID(t *testing.T) {
 }
 
 // ============================================================================
-// Stub coverage — every stub returns the not-enabled sentinel
+// Stub coverage — remaining stubs return the not-enabled sentinel
+//
+// CopyIndices / BatchUpdateChunkEnabledStatus / BatchUpdateChunkTagID are now
+// implemented (see copy_bulk_test.go for their behavioral tests); their stub
+// assertions were removed. EstimateStorageSize keeps its conservative
+// lower-bound until the real _stats-based implementation lands.
 // ============================================================================
 
-func TestStub_CopyIndices_ReturnsFeatureNotEnabled(t *testing.T) {
-	t.Parallel()
-	r := &Repository{}
-	err := r.CopyIndices(context.Background(), "kb1", nil, nil, "kb2", 768, "")
-	if !errors.Is(err, ErrFeatureNotEnabled) {
-		t.Errorf("CopyIndices: want ErrFeatureNotEnabled, got %v", err)
-	}
-}
-
-func TestStub_BatchUpdateChunkEnabledStatus_ReturnsFeatureNotEnabled(t *testing.T) {
-	t.Parallel()
-	r := &Repository{}
-	if err := r.BatchUpdateChunkEnabledStatus(context.Background(), nil); !errors.Is(err, ErrFeatureNotEnabled) {
-		t.Errorf("want ErrFeatureNotEnabled, got %v", err)
-	}
-}
-
-func TestStub_BatchUpdateChunkTagID_ReturnsFeatureNotEnabled(t *testing.T) {
-	t.Parallel()
-	r := &Repository{}
-	if err := r.BatchUpdateChunkTagID(context.Background(), nil); !errors.Is(err, ErrFeatureNotEnabled) {
-		t.Errorf("want ErrFeatureNotEnabled, got %v", err)
-	}
-}
-
 func TestStub_EstimateStorageSize_EmptyZero_NonEmptyPositive(t *testing.T) {
 	t.Parallel()
 	r := &Repository{}
diff --git a/internal/application/repository/retriever/opensearch/stubs.go b/internal/application/repository/retriever/opensearch/stubs.go
index 668ddb23..97ee584d 100644
--- a/internal/application/repository/retriever/opensearch/stubs.go
+++ b/internal/application/repository/retriever/opensearch/stubs.go
@@ -6,43 +6,12 @@ import (
 	"github.com/Tencent/WeKnora/internal/types"
 )
 
-// This file holds the remaining stubs for methods whose real
-// implementation has not landed yet — the async / batch paths and the
-// rolling-reindex swap. Each stub returns ErrFeatureNotEnabled (or, for
-// EstimateStorageSize, a conservative lower-bound) so any accidental
-// invocation surfaces loudly. The driver as a whole is still gated dead
-// code (no registry / factory / env path mentions it); these stubs
-// disappear when their behaviours arrive in follow-up commits.
-
-// CopyIndices: the async _reindex path with task polling for >10K-doc
-// batches arrives in a later change.
-func (r *Repository) CopyIndices(
-	_ context.Context,
-	_ string, // sourceKnowledgeBaseID
-	_ map[string]string, // sourceToTargetKBIDMap
-	_ map[string]string, // sourceToTargetChunkIDMap
-	_ string, // targetKnowledgeBaseID
-	_ int, // dimension
-	_ string, // knowledgeType
-) error {
-	return ErrFeatureNotEnabled
-}
-
-// BatchUpdateChunkEnabledStatus: the _update_by_query path arrives in a
-// later change.
-func (r *Repository) BatchUpdateChunkEnabledStatus(
-	_ context.Context, _ map[string]bool,
-) error {
-	return ErrFeatureNotEnabled
-}
-
-// BatchUpdateChunkTagID: the _update_by_query path arrives in a later
-// change.
-func (r *Repository) BatchUpdateChunkTagID(
-	_ context.Context, _ map[string]string,
-) error {
-	return ErrFeatureNotEnabled
-}
+// This file holds the remaining stubs for methods whose real implementation
+// has not landed yet — the rolling-reindex swap (swapToVersion) and the
+// precise storage estimate. CopyIndices (copy.go), BatchUpdateChunkEnabledStatus
+// and BatchUpdateChunkTagID (bulk_update.go) are now implemented. Each
+// remaining stub returns ErrFeatureNotEnabled (or, for EstimateStorageSize, a
+// conservative lower-bound) so any accidental invocation surfaces loudly.
 
 // EstimateStorageSize: the real implementation that reads cluster
 // `_stats` for the per-dim alias arrives in a later change. For now we
diff --git a/internal/application/repository/retriever/opensearch/transport.go b/internal/application/repository/retriever/opensearch/transport.go
index 1e1dc86c..c39fda27 100644
--- a/internal/application/repository/retriever/opensearch/transport.go
+++ b/internal/application/repository/retriever/opensearch/transport.go
@@ -12,12 +12,10 @@ import (
 	"github.com/Tencent/WeKnora/internal/types"
 )
 
-// newOpenSearchClient builds a TLS-hardened, pool-tuned *osapi.Client for
+// NewOpenSearchClient builds a TLS-hardened, pool-tuned *osapi.Client for
 // the OpenSearch driver. The caller wires it into the registry from the
 // env path (container) and the DB-store path (engine factory); the
-// Repository constructor itself receives the pre-built client. While the
-// driver is still gated dead code, no code path here is reachable from
-// production — the activation switch lands in a later change.
+// Repository constructor itself receives the pre-built client.
 //
 // TLS posture:
 //   - MinVersion: TLS 1.2 (TLS 1.3 negotiated when both ends support).
@@ -33,7 +31,7 @@ import (
 //   - IdleConnTimeout:     90s  (typical LB keep-alive)
 //   - ResponseHeaderTimeout: 30s (per-request safety net)
 //   - ExpectContinueTimeout: 1s
-func newOpenSearchClient(cfg *types.ConnectionConfig) (*osapi.Client, error) {
+func NewOpenSearchClient(cfg *types.ConnectionConfig) (*osapi.Client, error) {
 	if cfg == nil || cfg.Addr == "" {
 		return nil, fmt.Errorf("opensearch: ConnectionConfig.Addr required: %w", ErrConfigInvalid)
 	}
diff --git a/internal/application/repository/retriever/opensearch/transport_test.go b/internal/application/repository/retriever/opensearch/transport_test.go
index 173712ac..f2205c1b 100644
--- a/internal/application/repository/retriever/opensearch/transport_test.go
+++ b/internal/application/repository/retriever/opensearch/transport_test.go
@@ -14,11 +14,11 @@ import (
 // transport error later.
 func TestNewOpenSearchClient_RejectsEmptyAddr(t *testing.T) {
 	t.Parallel()
-	_, err := newOpenSearchClient(&types.ConnectionConfig{Addr: ""})
+	_, err := NewOpenSearchClient(&types.ConnectionConfig{Addr: ""})
 	if !errors.Is(err, ErrConfigInvalid) {
 		t.Fatalf("empty addr: want ErrConfigInvalid, got %v", err)
 	}
-	_, err = newOpenSearchClient(nil)
+	_, err = NewOpenSearchClient(nil)
 	if !errors.Is(err, ErrConfigInvalid) {
 		t.Fatalf("nil cfg: want ErrConfigInvalid, got %v", err)
 	}
@@ -30,13 +30,13 @@ func TestNewOpenSearchClient_RejectsEmptyAddr(t *testing.T) {
 // returns successfully.
 func TestNewOpenSearchClient_Succeeds_OnValidAddr(t *testing.T) {
 	t.Parallel()
-	client, err := newOpenSearchClient(&types.ConnectionConfig{
+	client, err := NewOpenSearchClient(&types.ConnectionConfig{
 		Addr:     "https://opensearch.example.com:9200",
 		Username: "admin",
 		Password: "secret", // not a real password — wire-format only
 	})
 	if err != nil {
-		t.Fatalf("newOpenSearchClient: %v", err)
+		t.Fatalf("NewOpenSearchClient: %v", err)
 	}
 	if client == nil {
 		t.Fatal("client must be non-nil on success")
diff --git a/internal/application/service/vectorstore.go b/internal/application/service/vectorstore.go
index af7562b9..a15c18b3 100644
--- a/internal/application/service/vectorstore.go
+++ b/internal/application/service/vectorstore.go
@@ -67,6 +67,14 @@ func (s *vectorStoreService) CreateStore(ctx context.Context, store *types.Vecto
 		return err
 	}
 
+	// 2.6. Engine-specific index config validation (OpenSearch HNSW bounds).
+	// Create-only: UpdateStore mutates just the name, so this is not re-run there.
+	if store.EngineType == types.OpenSearchRetrieverEngineType {
+		if err := validateOpenSearchIndexConfig(store.IndexConfig); err != nil {
+			return err
+		}
+	}
+
 	// 3. Duplicate check — DB stores
 	endpoint := store.ConnectionConfig.GetEndpoint()
 	indexName := store.IndexConfig.GetIndexNameOrDefault(store.EngineType)
@@ -452,8 +460,51 @@ func validateConnectionConfig(engineType types.RetrieverEngineType, config types
 		if config.Database == "" {
 			return errors.NewValidationError("database is required for doris")
 		}
+	case types.OpenSearchRetrieverEngineType:
+		if config.Addr == "" {
+			return errors.NewValidationError("addr is required for opensearch")
+		}
 	case types.SQLiteRetrieverEngineType:
 		// No connection config needed for SQLite
 	}
 	return nil
 }
+
+// openSearch HNSW bound constants. Shards / replicas are NOT validated here —
+// the flat types.ValidateIndexConfig already enforces those caps for every
+// engine. These caps mirror the GetVectorStoreTypes Min/Max so the UI and
+// backend agree. A zero / empty field means "use the driver default" and is
+// always accepted.
+const (
+	osHNSWMMin              = 2
+	osHNSWMMax              = 100
+	osHNSWEFConstructionMin = 2
+	osHNSWEFConstructionMax = 4096
+	osHNSWEFSearchMin       = 1
+	osHNSWEFSearchMax       = 10000
+)
+
+// validateOpenSearchIndexConfig validates the OpenSearch-specific HNSW fields.
+// Called from CreateStore only (the store is create-only; UpdateStore mutates
+// just the name). Unset fields (zero / empty) fall back to driver defaults and
+// are accepted.
+func validateOpenSearchIndexConfig(ic types.IndexConfig) error {
+	if ic.HNSWM != 0 && (ic.HNSWM < osHNSWMMin || ic.HNSWM > osHNSWMMax) {
+		return errors.NewValidationError(
+			fmt.Sprintf("hnsw_m must be between %d and %d", osHNSWMMin, osHNSWMMax))
+	}
+	if ic.HNSWEFConstruction != 0 &&
+		(ic.HNSWEFConstruction < osHNSWEFConstructionMin || ic.HNSWEFConstruction > osHNSWEFConstructionMax) {
+		return errors.NewValidationError(
+			fmt.Sprintf("hnsw_ef_construction must be between %d and %d", osHNSWEFConstructionMin, osHNSWEFConstructionMax))
+	}
+	if ic.HNSWEFSearch != 0 &&
+		(ic.HNSWEFSearch < osHNSWEFSearchMin || ic.HNSWEFSearch > osHNSWEFSearchMax) {
+		return errors.NewValidationError(
+			fmt.Sprintf("hnsw_ef_search must be between %d and %d", osHNSWEFSearchMin, osHNSWEFSearchMax))
+	}
+	if ic.KNNEngine != "" && ic.KNNEngine != "lucene" && ic.KNNEngine != "faiss" {
+		return errors.NewValidationError(`knn_engine must be "lucene" or "faiss"`)
+	}
+	return nil
+}
diff --git a/internal/application/service/vectorstore_healthcheck.go b/internal/application/service/vectorstore_healthcheck.go
index a27141fa..fca65e6b 100644
--- a/internal/application/service/vectorstore_healthcheck.go
+++ b/internal/application/service/vectorstore_healthcheck.go
@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	openSearchRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/opensearch"
 	"github.com/Tencent/WeKnora/internal/errors"
 	"github.com/Tencent/WeKnora/internal/logger"
 	"github.com/Tencent/WeKnora/internal/types"
@@ -47,6 +48,8 @@ func (s *vectorStoreService) TestConnection(
 		return testWeaviateConnection(ctx, config)
 	case types.DorisRetrieverEngineType:
 		return testDorisConnection(ctx, config)
+	case types.OpenSearchRetrieverEngineType:
+		return testOpenSearchConnection(ctx, config)
 	case types.SQLiteRetrieverEngineType:
 		// SQLite is file-based, no remote connection to test
 		return "", nil
@@ -305,3 +308,23 @@ func testDorisConnection(ctx context.Context, config types.ConnectionConfig) (st
 	}
 	return version, nil
 }
+
+// testOpenSearchConnection verifies the cluster is reachable, runs a
+// supported OpenSearch version, and has the k-NN plugin installed. The driver
+// owns the probe logic; a generic message is returned on failure so cluster
+// internals are not surfaced to the API caller.
+func testOpenSearchConnection(ctx context.Context, config types.ConnectionConfig) (string, error) {
+	if config.Addr == "" {
+		return "", errors.NewBadRequestError("failed to create opensearch connection: addr is required")
+	}
+	testCtx, cancel := context.WithTimeout(ctx, connectionTestTimeout)
+	defer cancel()
+	if err := openSearchRepo.TestConnection(testCtx, &config); err != nil {
+		logger.Warnf(ctx, "OpenSearch connection test failed: %v", err)
+		return "", errors.NewBadRequestError(
+			"failed to connect to opensearch: check address, credentials, version (>= 2.4), and that the k-NN plugin is installed")
+	}
+	// Version is detected during the probe but not surfaced here; lazy index
+	// creation re-validates on first use.
+	return "", nil
+}
diff --git a/internal/application/service/vectorstore_opensearch_test.go b/internal/application/service/vectorstore_opensearch_test.go
new file mode 100644
index 00000000..b587aa9b
--- /dev/null
+++ b/internal/application/service/vectorstore_opensearch_test.go
@@ -0,0 +1,47 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/Tencent/WeKnora/internal/types"
+)
+
+func TestValidateConnectionConfig_OpenSearch_RequiresAddr(t *testing.T) {
+	if err := validateConnectionConfig(types.OpenSearchRetrieverEngineType, types.ConnectionConfig{}); err == nil {
+		t.Error("empty addr should be rejected for opensearch")
+	}
+	if err := validateConnectionConfig(types.OpenSearchRetrieverEngineType,
+		types.ConnectionConfig{Addr: "https://os:9200"}); err != nil {
+		t.Errorf("valid addr should pass: %v", err)
+	}
+}
+
+func TestValidateOpenSearchIndexConfig_BoundaryMatrix(t *testing.T) {
+	tests := []struct {
+		name    string
+		ic      types.IndexConfig
+		wantErr bool
+	}{
+		{"all unset (defaults)", types.IndexConfig{}, false},
+		{"valid mid-range", types.IndexConfig{HNSWM: 16, HNSWEFConstruction: 100, HNSWEFSearch: 100, KNNEngine: "lucene"}, false},
+		{"valid faiss", types.IndexConfig{KNNEngine: "faiss"}, false},
+		{"valid boundaries", types.IndexConfig{HNSWM: 2, HNSWEFConstruction: 2, HNSWEFSearch: 1}, false},
+		{"valid upper boundaries", types.IndexConfig{HNSWM: 100, HNSWEFConstruction: 4096, HNSWEFSearch: 10000}, false},
+		{"hnsw_m too low", types.IndexConfig{HNSWM: 1}, true},
+		{"hnsw_m too high", types.IndexConfig{HNSWM: 101}, true},
+		{"ef_construction too high", types.IndexConfig{HNSWEFConstruction: 4097}, true},
+		{"ef_search too high", types.IndexConfig{HNSWEFSearch: 10001}, true},
+		{"invalid engine", types.IndexConfig{KNNEngine: "nmslib"}, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validateOpenSearchIndexConfig(tt.ic)
+			if tt.wantErr && err == nil {
+				t.Errorf("want error, got nil")
+			}
+			if !tt.wantErr && err != nil {
+				t.Errorf("want nil, got %v", err)
+			}
+		})
+	}
+}
diff --git a/internal/container/audit_sink.go b/internal/container/audit_sink.go
new file mode 100644
index 00000000..fab31d74
--- /dev/null
+++ b/internal/container/audit_sink.go
@@ -0,0 +1,66 @@
+package container
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/Tencent/WeKnora/internal/application/repository/retriever/opensearch"
+	"github.com/Tencent/WeKnora/internal/logger"
+	"github.com/Tencent/WeKnora/internal/types"
+	"github.com/Tencent/WeKnora/internal/types/interfaces"
+)
+
+// auditSinkAdapter bridges the OpenSearch driver's AuditSink (which the driver
+// owns so it imports no service package) to the service-layer AuditLogService.
+// This keeps the dependency one-way: the driver depends only on its own
+// AuditSink abstraction; the container implements it.
+type auditSinkAdapter struct {
+	svc interfaces.AuditLogService
+}
+
+// newAuditSinkAdapter returns an opensearch.AuditSink backed by svc. A nil svc
+// yields a sink whose emits are no-ops.
+func newAuditSinkAdapter(svc interfaces.AuditLogService) opensearch.AuditSink {
+	return auditSinkAdapter{svc: svc}
+}
+
+func (a auditSinkAdapter) EmitIndexCreated(ctx context.Context, alias string, dim int) {
+	a.emit(ctx, types.AuditActionOpenSearchIndexCreated, alias,
+		map[string]any{"alias": alias, "dim": dim})
+}
+
+func (a auditSinkAdapter) EmitReindexExecuted(ctx context.Context, srcAlias, dstAlias string, docs int64) {
+	a.emit(ctx, types.AuditActionOpenSearchReindexExecuted, dstAlias,
+		map[string]any{"src_alias": srcAlias, "dst_alias": dstAlias, "docs": docs})
+}
+
+// emit writes one audit entry. It skips (with a warning) when the context
+// carries no tenant — driver events can fire from background task contexts
+// (e.g. lazy index creation under an async copy task), and writing tenant_id=0
+// would collide with the system-scope sentinel and corrupt the audit trail.
+func (a auditSinkAdapter) emit(ctx context.Context, action types.AuditAction, target string, detail map[string]any) {
+	if a.svc == nil {
+		return
+	}
+	tid, ok := types.TenantIDFromContext(ctx)
+	if !ok {
+		logger.GetLogger(ctx).Warnf("[audit] %s: no tenant in context, skipping audit (target=%s)", action, target)
+		return
+	}
+	// Details is a typed JSON blob — only bounded, non-secret fields. Never
+	// include cluster reason strings or connection secrets.
+	b, err := json.Marshal(detail)
+	if err != nil {
+		logger.GetLogger(ctx).Warnf("[audit] %s: marshal details failed: %v", action, err)
+		b = []byte("{}")
+	}
+	if err := a.svc.Log(ctx, &types.AuditLog{
+		TenantID:   tid,
+		Action:     action,
+		TargetType: "opensearch_index",
+		TargetID:   target,
+		Details:    types.JSON(b),
+	}); err != nil {
+		logger.GetLogger(ctx).Warnf("[audit] %s emit failed: %v", action, err)
+	}
+}
diff --git a/internal/container/audit_sink_test.go b/internal/container/audit_sink_test.go
new file mode 100644
index 00000000..1ce9c8e6
--- /dev/null
+++ b/internal/container/audit_sink_test.go
@@ -0,0 +1,74 @@
+package container
+
+import (
+	"context"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/Tencent/WeKnora/internal/types"
+	"github.com/Tencent/WeKnora/internal/types/interfaces"
+)
+
+// fakeAuditSvc records Log calls.
+type fakeAuditSvc struct {
+	logged []*types.AuditLog
+	err    error
+}
+
+func (f *fakeAuditSvc) Log(_ context.Context, e *types.AuditLog) error {
+	f.logged = append(f.logged, e)
+	return f.err
+}
+func (f *fakeAuditSvc) LogDenied(context.Context, *gin.Context, uint64, string, string, types.TenantRole) error {
+	return nil
+}
+func (f *fakeAuditSvc) List(context.Context, uint64, *interfaces.AuditLogQuery) ([]*types.AuditLog, error) {
+	return nil, nil
+}
+func (f *fakeAuditSvc) Purge(context.Context, int) (int64, error) { return 0, nil }
+
+func ctxWithTenant(id uint64) context.Context {
+	return context.WithValue(context.Background(), types.TenantIDContextKey, id)
+}
+
+func TestAuditSinkAdapter_EmitsWithTenant(t *testing.T) {
+	f := &fakeAuditSvc{}
+	sink := newAuditSinkAdapter(f)
+
+	sink.EmitIndexCreated(ctxWithTenant(42), "weknora_768", 768)
+	if len(f.logged) != 1 {
+		t.Fatalf("want 1 audit entry, got %d", len(f.logged))
+	}
+	e := f.logged[0]
+	if e.TenantID != 42 {
+		t.Errorf("tenant: want 42, got %d", e.TenantID)
+	}
+	if e.Action != types.AuditActionOpenSearchIndexCreated {
+		t.Errorf("action: want %s, got %s", types.AuditActionOpenSearchIndexCreated, e.Action)
+	}
+	if e.Details == nil {
+		t.Error("details should be populated")
+	}
+
+	sink.EmitReindexExecuted(ctxWithTenant(7), "src", "dst", 9)
+	if len(f.logged) != 2 || f.logged[1].Action != types.AuditActionOpenSearchReindexExecuted {
+		t.Errorf("reindex audit not recorded: %+v", f.logged)
+	}
+}
+
+func TestAuditSinkAdapter_SkipsWithoutTenant(t *testing.T) {
+	f := &fakeAuditSvc{}
+	sink := newAuditSinkAdapter(f)
+	// background ctx carries no tenant → adapter must skip (never write tenant=0)
+	sink.EmitIndexCreated(context.Background(), "weknora_768", 768)
+	sink.EmitReindexExecuted(context.Background(), "a", "b", 1)
+	if len(f.logged) != 0 {
+		t.Errorf("want 0 audit entries without tenant, got %d", len(f.logged))
+	}
+}
+
+func TestAuditSinkAdapter_NilServiceNoPanic(t *testing.T) {
+	sink := newAuditSinkAdapter(nil)
+	sink.EmitIndexCreated(ctxWithTenant(1), "x", 1) // must not panic
+}
diff --git a/internal/container/container.go b/internal/container/container.go
index 3c582287..c53d3f5c 100644
--- a/internal/container/container.go
+++ b/internal/container/container.go
@@ -40,6 +40,7 @@ import (
 	elasticsearchRepoV8 "github.com/Tencent/WeKnora/internal/application/repository/retriever/elasticsearch/v8"
 	milvusRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/milvus"
 	neo4jRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/neo4j"
+	openSearchRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/opensearch"
 	postgresRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/postgres"
 	qdrantRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/qdrant"
 	sqliteRetrieverRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/sqlite"
@@ -785,10 +786,16 @@ func initFileService(cfg *config.Config) (interfaces.FileService, error) {
 // Returns:
 //   - Configured retrieval engine registry
 //   - Error if initialization fails
-func initRetrieveEngineRegistry(db *gorm.DB, cfg *config.Config) (interfaces.RetrieveEngineRegistry, error) {
+func initRetrieveEngineRegistry(
+	db *gorm.DB, cfg *config.Config, auditSvc interfaces.AuditLogService,
+) (interfaces.RetrieveEngineRegistry, error) {
 	registry := retriever.NewRetrieveEngineRegistry()
 	retrieveDriver := strings.Split(os.Getenv("RETRIEVE_DRIVER"), ",")
 	log := logger.GetLogger(context.Background())
+	// Audit sink for OpenSearch driver events (index created / reindex). Driver
+	// events fire under a tenant-scoped ctx at indexing time; the env-path
+	// registration ctx below has no tenant, so those emits self-skip.
+	auditSink := newAuditSinkAdapter(auditSvc)
 
 	if slices.Contains(retrieveDriver, "postgres") {
 		postgresRepo := postgresRepo.NewPostgresRetrieveEngineRepository(db)
@@ -854,6 +861,29 @@ func initRetrieveEngineRegistry(db *gorm.DB, cfg *config.Config) (interfaces.Ret
 		}
 	}
 
+	if slices.Contains(retrieveDriver, "opensearch") {
+		cc := &types.ConnectionConfig{
+			Addr:               os.Getenv("OPENSEARCH_ADDR"),
+			Username:           os.Getenv("OPENSEARCH_USERNAME"),
+			Password:           os.Getenv("OPENSEARCH_PASSWORD"),
+			InsecureSkipVerify: strings.EqualFold(os.Getenv("OPENSEARCH_INSECURE_SKIP_VERIFY"), "true"),
+		}
+		client, err := openSearchRepo.NewOpenSearchClient(cc)
+		if err != nil {
+			log.Errorf("Create opensearch client failed: %v", err)
+		} else if repo, err := openSearchRepo.NewRepository(
+			context.Background(), client, "", nil, openSearchRepo.WithAuditSink(auditSink),
+		); err != nil {
+			log.Errorf("Create opensearch repository failed: %v", err)
+		} else if err := registry.Register(
+			retriever.NewKVHybridRetrieveEngine(repo, types.OpenSearchRetrieverEngineType),
+		); err != nil {
+			log.Errorf("Register opensearch retrieve engine failed: %v", err)
+		} else {
+			log.Infof("Register opensearch retrieve engine success")
+		}
+	}
+
 	if slices.Contains(retrieveDriver, "qdrant") {
 		qdrantHost := os.Getenv("QDRANT_HOST")
 		if qdrantHost == "" {
@@ -1061,7 +1091,7 @@ func initRetrieveEngineRegistry(db *gorm.DB, cfg *config.Config) (interfaces.Ret
 	}
 	// ─── DB store registration (byStoreID) ───
 	if storeReg, ok := registry.(*retriever.RetrieveEngineRegistry); ok {
-		loadDBStoresIntoRegistry(storeReg, db, cfg)
+		loadDBStoresIntoRegistry(storeReg, db, cfg, auditSink)
 	}
 
 	return registry, nil
@@ -1069,7 +1099,9 @@ func initRetrieveEngineRegistry(db *gorm.DB, cfg *config.Config) (interfaces.Ret
 
 // loadDBStoresIntoRegistry loads VectorStore records from DB and registers them
 // in the registry's byStoreID map. Failures are logged and skipped (non-fatal).
-func loadDBStoresIntoRegistry(storeRegistry interfaces.StoreRegistry, db *gorm.DB, cfg *config.Config) {
+func loadDBStoresIntoRegistry(
+	storeRegistry interfaces.StoreRegistry, db *gorm.DB, cfg *config.Config, auditSink openSearchRepo.AuditSink,
+) {
 	ctx := context.Background()
 	log := logger.GetLogger(ctx)
 
@@ -1086,7 +1118,7 @@ func loadDBStoresIntoRegistry(storeRegistry interfaces.StoreRegistry, db *gorm.D
 
 	log.Infof("Loading %d vector store(s) from database", len(stores))
 	for _, store := range stores {
-		svc, err := createEngineServiceFromStore(ctx, store, db, cfg)
+		svc, err := createEngineServiceFromStore(ctx, store, db, cfg, auditSink)
 		if err != nil {
 			log.Errorf("Failed to create engine for store %s (%s): %v", store.ID, store.Name, err)
 			continue
diff --git a/internal/container/engine_factory.go b/internal/container/engine_factory.go
index 44a16888..2e09f15a 100644
--- a/internal/container/engine_factory.go
+++ b/internal/container/engine_factory.go
@@ -23,6 +23,7 @@ import (
 	elasticsearchRepoV7 "github.com/Tencent/WeKnora/internal/application/repository/retriever/elasticsearch/v7"
 	elasticsearchRepoV8 "github.com/Tencent/WeKnora/internal/application/repository/retriever/elasticsearch/v8"
 	milvusRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/milvus"
+	openSearchRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/opensearch"
 	postgresRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/postgres"
 	qdrantRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/qdrant"
 	sqliteRetrieverRepo "github.com/Tencent/WeKnora/internal/application/repository/retriever/sqlite"
@@ -35,21 +36,27 @@ import (
 	"github.com/tencent/vectordatabase-sdk-go/tcvectordb"
 )
 
-// NewEngineFactory returns an EngineFactory function closed over db and cfg.
-// Registered in dig and injected into VectorStoreService for dynamic registry updates.
-func NewEngineFactory(db *gorm.DB, cfg *config.Config) interfaces.EngineFactory {
+// NewEngineFactory returns an EngineFactory function closed over db, cfg, and
+// an audit sink (built from the AuditLogService). Registered in dig and
+// injected into VectorStoreService for dynamic registry updates. The
+// EngineFactory type itself is unchanged — the audit sink is captured in the
+// closure rather than added to the signature.
+func NewEngineFactory(db *gorm.DB, cfg *config.Config, auditSvc interfaces.AuditLogService) interfaces.EngineFactory {
+	sink := newAuditSinkAdapter(auditSvc)
 	return func(ctx context.Context, store types.VectorStore) (interfaces.RetrieveEngineService, error) {
-		return createEngineServiceFromStore(ctx, store, db, cfg)
+		return createEngineServiceFromStore(ctx, store, db, cfg, sink)
 	}
 }
 
 // createEngineServiceFromStore creates a RetrieveEngineService from a VectorStore's config.
 // This is the DB store counterpart of the env-based initialization in initRetrieveEngineRegistry.
+// auditSink may be nil (audit becomes a no-op).
 func createEngineServiceFromStore(
 	ctx context.Context,
 	store types.VectorStore,
 	db *gorm.DB,
 	cfg *config.Config,
+	auditSink openSearchRepo.AuditSink,
 ) (interfaces.RetrieveEngineService, error) {
 	switch store.EngineType {
 	case types.PostgresRetrieverEngineType:
@@ -68,11 +75,40 @@ func createEngineServiceFromStore(
 		return createSQLiteEngine(store, db)
 	case types.TencentVectorDBRetrieverEngineType:
 		return createTencentVectorDBEngine(store)
+	case types.OpenSearchRetrieverEngineType:
+		return createOpenSearchEngine(ctx, store, auditSink)
 	default:
 		return nil, fmt.Errorf("unsupported engine type: %s", store.EngineType)
 	}
 }
 
+// createOpenSearchEngine builds an OpenSearch k-NN retrieve engine. Mirrors
+// createElasticsearchV8Engine but uses the driver's TLS-hardened client
+// constructor and injects the audit sink. NewRepository probes the cluster
+// (version + k-NN plugin), so an unreachable cluster fails here at
+// registration rather than on first query.
+func createOpenSearchEngine(
+	ctx context.Context, store types.VectorStore, auditSink openSearchRepo.AuditSink,
+) (interfaces.RetrieveEngineService, error) {
+	client, err := openSearchRepo.NewOpenSearchClient(&store.ConnectionConfig)
+	if err != nil {
+		return nil, fmt.Errorf("create opensearch client: %w", err)
+	}
+	// Env stores share the cluster without a per-store index prefix; DB stores
+	// fold their (>=16-char) ID into the index name. NewRepository enforces the
+	// length rule, so map env-store IDs to "".
+	storeID := store.ID
+	if types.IsEnvStoreID(storeID) {
+		storeID = ""
+	}
+	repo, err := openSearchRepo.NewRepository(ctx, client, storeID, &store.IndexConfig,
+		openSearchRepo.WithAuditSink(auditSink))
+	if err != nil {
+		return nil, fmt.Errorf("create opensearch repository: %w", err)
+	}
+	return retriever.NewKVHybridRetrieveEngine(repo, types.OpenSearchRetrieverEngineType), nil
+}
+
 func createPostgresEngine(store types.VectorStore, db *gorm.DB) (interfaces.RetrieveEngineService, error) {
 	if store.ConnectionConfig.UseDefaultConnection {
 		repo := postgresRepo.NewPostgresRetrieveEngineRepository(db)
diff --git a/internal/container/engine_factory_opensearch_test.go b/internal/container/engine_factory_opensearch_test.go
new file mode 100644
index 00000000..d21c1c81
--- /dev/null
+++ b/internal/container/engine_factory_opensearch_test.go
@@ -0,0 +1,104 @@
+package container
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+
+	"github.com/Tencent/WeKnora/internal/config"
+	"github.com/Tencent/WeKnora/internal/types"
+)
+
+// osClusterHandler simulates an OpenSearch cluster for the driver's
+// construction probe: GET / (version) + /_cat/plugins (k-NN on every node).
+func osClusterHandler(distribution, number string, knnInstalled bool) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		if r.URL.Path == "/_cat/plugins" {
+			if knnInstalled {
+				_, _ = w.Write([]byte(`[{"name":"node-1","component":"opensearch-knn"}]`))
+			} else {
+				_, _ = w.Write([]byte(`[{"name":"node-1","component":"opensearch-sql"}]`))
+			}
+			return
+		}
+		_, _ = w.Write([]byte(`{"version":{"distribution":"` + distribution + `","number":"` + number + `"}}`))
+	}
+}
+
+func TestCreateOpenSearchEngine_WiresClientAndRepo(t *testing.T) {
+	ts := httptest.NewServer(osClusterHandler("opensearch", "3.3.2", true))
+	defer ts.Close()
+
+	store := types.VectorStore{
+		ID:               "", // env-style (no index prefix)
+		EngineType:       types.OpenSearchRetrieverEngineType,
+		ConnectionConfig: types.ConnectionConfig{Addr: ts.URL},
+	}
+	svc, err := createOpenSearchEngine(context.Background(), store, nil)
+	if err != nil {
+		t.Fatalf("createOpenSearchEngine: %v", err)
+	}
+	if svc == nil {
+		t.Fatal("want non-nil engine service")
+	}
+	if svc.EngineType() != types.OpenSearchRetrieverEngineType {
+		t.Errorf("engine type: want opensearch, got %s", svc.EngineType())
+	}
+}
+
+func TestCreateOpenSearchEngine_RejectsBadCluster(t *testing.T) {
+	// Elasticsearch distribution must be rejected at construction.
+	ts := httptest.NewServer(osClusterHandler("elasticsearch", "8.10.4", true))
+	defer ts.Close()
+	_, err := createOpenSearchEngine(context.Background(),
+		types.VectorStore{EngineType: types.OpenSearchRetrieverEngineType,
+			ConnectionConfig: types.ConnectionConfig{Addr: ts.URL}}, nil)
+	if err == nil {
+		t.Error("elasticsearch cluster should be rejected at engine creation")
+	}
+}
+
+func TestCreateEngineServiceFromStore_OpenSearchCaseReached(t *testing.T) {
+	ts := httptest.NewServer(osClusterHandler("opensearch", "2.11.0", true))
+	defer ts.Close()
+	svc, err := createEngineServiceFromStore(context.Background(),
+		types.VectorStore{EngineType: types.OpenSearchRetrieverEngineType,
+			ConnectionConfig: types.ConnectionConfig{Addr: ts.URL}},
+		nil, &config.Config{}, nil)
+	if err != nil {
+		t.Fatalf("createEngineServiceFromStore (opensearch case): %v", err)
+	}
+	if svc == nil || svc.EngineType() != types.OpenSearchRetrieverEngineType {
+		t.Errorf("opensearch case not wired correctly: %v", svc)
+	}
+}
+
+// TestInitRetrieveEngineRegistry_OpenSearchEnvPath exercises the
+// RETRIEVE_DRIVER=opensearch env-path registration block end to end.
+func TestInitRetrieveEngineRegistry_OpenSearchEnvPath(t *testing.T) {
+	ts := httptest.NewServer(osClusterHandler("opensearch", "3.3.2", true))
+	defer ts.Close()
+
+	// In-memory DB: the vector_stores table is absent, so loadDBStores logs
+	// and returns (non-fatal) — only the env-path block matters here.
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("open in-mem db: %v", err)
+	}
+
+	t.Setenv("RETRIEVE_DRIVER", "opensearch")
+	t.Setenv("OPENSEARCH_ADDR", ts.URL)
+
+	registry, err := initRetrieveEngineRegistry(db, &config.Config{}, &fakeAuditSvc{})
+	if err != nil {
+		t.Fatalf("initRetrieveEngineRegistry: %v", err)
+	}
+	if _, err := registry.GetRetrieveEngineService(types.OpenSearchRetrieverEngineType); err != nil {
+		t.Errorf("opensearch engine not registered via env path: %v", err)
+	}
+}
diff --git a/internal/types/tenant.go b/internal/types/tenant.go
index 983e8d7a..e4a5825c 100644
--- a/internal/types/tenant.go
+++ b/internal/types/tenant.go
@@ -50,6 +50,10 @@ var retrieverEngineMapping = map[string][]RetrieverEngineParams{
 		{RetrieverType: KeywordsRetrieverType, RetrieverEngineType: TencentVectorDBRetrieverEngineType},
 		{RetrieverType: VectorRetrieverType, RetrieverEngineType: TencentVectorDBRetrieverEngineType},
 	},
+	"opensearch": {
+		{RetrieverType: KeywordsRetrieverType, RetrieverEngineType: OpenSearchRetrieverEngineType},
+		{RetrieverType: VectorRetrieverType, RetrieverEngineType: OpenSearchRetrieverEngineType},
+	},
 }
 
 // GetRetrieverEngineMapping returns the retriever engine mapping
diff --git a/internal/types/vectorstore.go b/internal/types/vectorstore.go
index 865d1615..ae970490 100644
--- a/internal/types/vectorstore.go
+++ b/internal/types/vectorstore.go
@@ -86,6 +86,7 @@ var validEngineTypes = map[RetrieverEngineType]bool{
 	WeaviateRetrieverEngineType:        true,
 	DorisRetrieverEngineType:           true,
 	TencentVectorDBRetrieverEngineType: true,
+	OpenSearchRetrieverEngineType:      true,
 }
 
 // IsValidEngineType checks whether the given engine type is valid for VectorStore.
@@ -250,6 +251,14 @@ type IndexConfig struct {
 	DesiredShardCount int `yaml:"desired_shard_count" json:"desired_shard_count,omitempty"` // Weaviate: number of shards per collection
 	BucketsNum        int `yaml:"buckets_num" json:"buckets_num,omitempty"`                 // Doris: number of buckets per table (DISTRIBUTED BY HASH ... BUCKETS N)
 	ReplicationNum    int `yaml:"replication_num" json:"replication_num,omitempty"`         // Doris: replication_num PROPERTIES
+
+	// --- OpenSearch k-NN HNSW fields ---
+	// All omitempty so other engines' serialized IndexConfig is unchanged.
+	// Zero / empty values fall back to the driver defaults in buildInternalCfg.
+	HNSWM              int    `yaml:"hnsw_m" json:"hnsw_m,omitempty"`                             // OpenSearch: HNSW graph degree (M)
+	HNSWEFConstruction int    `yaml:"hnsw_ef_construction" json:"hnsw_ef_construction,omitempty"` // OpenSearch: HNSW index-build candidate list size
+	HNSWEFSearch       int    `yaml:"hnsw_ef_search" json:"hnsw_ef_search,omitempty"`             // OpenSearch: HNSW search candidate list size (faiss; lucene reads at query time)
+	KNNEngine          string `yaml:"knn_engine" json:"knn_engine,omitempty"`                     // OpenSearch: k-NN backend ("lucene" | "faiss")
 }
 
 // Value implements the driver.Valuer interface.
@@ -727,9 +736,32 @@ func GetVectorStoreTypes() []VectorStoreTypeInfo {
 				{Name: "replication_num", Type: "number", Required: false, Description: "Replication Num", Default: 1},
 			},
 		},
+		{
+			Type:        "opensearch",
+			DisplayName: "OpenSearch",
+			ConnectionFields: []VectorStoreFieldInfo{
+				{Name: "addr", Type: "string", Required: true, Description: "URL", Default: "https://localhost:9200"},
+				{Name: "username", Type: "string", Required: false, Description: "Username", Default: "admin"},
+				{Name: "password", Type: "string", Required: false, Sensitive: true, Description: "Password"},
+				{Name: "insecure_skip_verify", Type: "boolean", Required: false, Default: false,
+					Description: "Skip TLS certificate verification. For self-signed dev clusters only — never enable in production."},
+			},
+			IndexFields: []VectorStoreFieldInfo{
+				{Name: "index_name", Type: "string", Required: false, Description: "Index Name", Default: "weknora"},
+				{Name: "number_of_shards", Type: "number", Required: false, Description: "Shards", Default: 4, Min: floatPtr(1), Max: floatPtr(64)},
+				{Name: "number_of_replicas", Type: "number", Required: false, Description: "Replicas", Default: 1, Min: floatPtr(0), Max: floatPtr(10)},
+				{Name: "hnsw_m", Type: "number", Required: false, Description: "HNSW graph degree (M). Immutable after index creation.", Default: 16, Min: floatPtr(2), Max: floatPtr(100), Immutable: true},
+				{Name: "hnsw_ef_construction", Type: "number", Required: false, Description: "HNSW build candidate list. Higher (e.g. 200-512) improves recall at the cost of build time. Immutable after creation.", Default: 100, Min: floatPtr(2), Max: floatPtr(4096), Immutable: true},
+				{Name: "hnsw_ef_search", Type: "number", Required: false, Description: "HNSW search candidate list. Effective on the faiss engine; the lucene engine reads it at query time. Immutable (no settings-update path).", Default: 100, Min: floatPtr(1), Max: floatPtr(10000), Immutable: true},
+				{Name: "knn_engine", Type: "string", Required: false, Description: "k-NN backend.", Default: "lucene", Enum: []string{"lucene", "faiss"}, Immutable: true},
+			},
+		},
 	}
 }
 
+// floatPtr returns a pointer to v, for setting VectorStoreFieldInfo Min/Max.
+func floatPtr(v float64) *float64 { return &v }
+
 // ---------------------------------------------------------------------------
 // BuildEnvVectorStores — virtual stores from RETRIEVE_DRIVER env var
 // ---------------------------------------------------------------------------
@@ -821,6 +853,21 @@ func buildEnvStoreForDriver(driver string, envLookup EnvLookupFunc) *VectorStore
 				IndexName: envLookup("ELASTICSEARCH_INDEX"),
 			},
 		}
+	case "opensearch":
+		return &VectorStore{
+			ID:         "__env_opensearch__",
+			Name:       "OpenSearch",
+			EngineType: OpenSearchRetrieverEngineType,
+			ConnectionConfig: ConnectionConfig{
+				Addr:               envLookup("OPENSEARCH_ADDR"),
+				Username:           envLookup("OPENSEARCH_USERNAME"),
+				Password:           envLookup("OPENSEARCH_PASSWORD"),
+				InsecureSkipVerify: strings.EqualFold(envLookup("OPENSEARCH_INSECURE_SKIP_VERIFY"), "true"),
+			},
+			IndexConfig: IndexConfig{
+				IndexName: envLookup("OPENSEARCH_INDEX"),
+			},
+		}
 	case "qdrant":
 		return &VectorStore{
 			ID:         "__env_qdrant__",
diff --git a/internal/types/vectorstore_opensearch_test.go b/internal/types/vectorstore_opensearch_test.go
new file mode 100644
index 00000000..76eb583a
--- /dev/null
+++ b/internal/types/vectorstore_opensearch_test.go
@@ -0,0 +1,154 @@
+package types
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// findVSType returns the VectorStoreTypeInfo with the given Type, or fails.
+func findVSType(t *testing.T, typeName string) VectorStoreTypeInfo {
+	t.Helper()
+	for _, vt := range GetVectorStoreTypes() {
+		if vt.Type == typeName {
+			return vt
+		}
+	}
+	t.Fatalf("GetVectorStoreTypes() has no entry for %q", typeName)
+	return VectorStoreTypeInfo{}
+}
+
+// findField returns the field with the given Name from a slice, or fails.
+func findField(t *testing.T, fields []VectorStoreFieldInfo, name string) VectorStoreFieldInfo {
+	t.Helper()
+	for _, f := range fields {
+		if f.Name == name {
+			return f
+		}
+	}
+	t.Fatalf("no field named %q", name)
+	return VectorStoreFieldInfo{}
+}
+
+// TestIndexConfig_OpenSearchFieldsOmittedForOtherEngines verifies the new HNSW
+// fields are omitempty so other engines' serialized IndexConfig is unchanged.
+func TestIndexConfig_OpenSearchFieldsOmittedForOtherEngines(t *testing.T) {
+	t.Run("omitted when unset", func(t *testing.T) {
+		b, err := json.Marshal(IndexConfig{IndexName: "weknora", NumberOfShards: 4})
+		require.NoError(t, err)
+		s := string(b)
+		assert.NotContains(t, s, "hnsw_m")
+		assert.NotContains(t, s, "hnsw_ef_construction")
+		assert.NotContains(t, s, "hnsw_ef_search")
+		assert.NotContains(t, s, "knn_engine")
+	})
+
+	t.Run("present when set", func(t *testing.T) {
+		b, err := json.Marshal(IndexConfig{
+			HNSWM:              24,
+			HNSWEFConstruction: 200,
+			HNSWEFSearch:       128,
+			KNNEngine:          "faiss",
+		})
+		require.NoError(t, err)
+		s := string(b)
+		assert.Contains(t, s, `"hnsw_m":24`)
+		assert.Contains(t, s, `"hnsw_ef_construction":200`)
+		assert.Contains(t, s, `"hnsw_ef_search":128`)
+		assert.Contains(t, s, `"knn_engine":"faiss"`)
+	})
+}
+
+// TestIsValidEngineType_OpenSearch verifies OpenSearch is now a valid DB-store engine.
+func TestIsValidEngineType_OpenSearch(t *testing.T) {
+	assert.True(t, IsValidEngineType(OpenSearchRetrieverEngineType))
+}
+
+// TestGetVectorStoreTypes_OpenSearchEntry verifies the OpenSearch metadata entry
+// exposes the connection + HNSW index fields with the right bounds/enum/immutable.
+func TestGetVectorStoreTypes_OpenSearchEntry(t *testing.T) {
+	vt := findVSType(t, "opensearch")
+	assert.Equal(t, "OpenSearch", vt.DisplayName)
+
+	// Connection fields
+	insecure := findField(t, vt.ConnectionFields, "insecure_skip_verify")
+	assert.Equal(t, "boolean", insecure.Type)
+	assert.Equal(t, false, insecure.Default) // never default-true
+	pw := findField(t, vt.ConnectionFields, "password")
+	assert.True(t, pw.Sensitive)
+
+	// HNSW index fields: bounds match the flat-validator-aligned caps (14-D)
+	m := findField(t, vt.IndexFields, "hnsw_m")
+	require.NotNil(t, m.Min)
+	require.NotNil(t, m.Max)
+	assert.Equal(t, 2.0, *m.Min)
+	assert.Equal(t, 100.0, *m.Max)
+	assert.True(t, m.Immutable)
+
+	shards := findField(t, vt.IndexFields, "number_of_shards")
+	require.NotNil(t, shards.Max)
+	assert.Equal(t, 64.0, *shards.Max) // flat ValidateIndexConfig maxShards
+
+	replicas := findField(t, vt.IndexFields, "number_of_replicas")
+	require.NotNil(t, replicas.Max)
+	assert.Equal(t, 10.0, *replicas.Max) // flat maxReplicas
+
+	eng := findField(t, vt.IndexFields, "knn_engine")
+	assert.ElementsMatch(t, []string{"lucene", "faiss"}, eng.Enum)
+	assert.True(t, eng.Immutable)
+
+	efs := findField(t, vt.IndexFields, "hnsw_ef_search")
+	assert.True(t, efs.Immutable) // no PutSettings path → immutable
+}
+
+// TestBuildEnvVectorStores_OpenSearch verifies the env-store builder case.
+func TestBuildEnvVectorStores_OpenSearch(t *testing.T) {
+	lookup := mockEnvLookup(map[string]string{
+		"OPENSEARCH_ADDR":                 "https://os:9200",
+		"OPENSEARCH_USERNAME":             "admin",
+		"OPENSEARCH_PASSWORD":             "secret",
+		"OPENSEARCH_INDEX":                "weknora",
+		"OPENSEARCH_INSECURE_SKIP_VERIFY": "true",
+	})
+	stores := BuildEnvVectorStores("opensearch", lookup)
+	require.Len(t, stores, 1)
+	s := stores[0]
+	assert.Equal(t, "__env_opensearch__", s.ID)
+	assert.Equal(t, OpenSearchRetrieverEngineType, s.EngineType)
+	assert.Equal(t, "https://os:9200", s.ConnectionConfig.Addr)
+	assert.Equal(t, "admin", s.ConnectionConfig.Username)
+	assert.Equal(t, "secret", s.ConnectionConfig.Password)
+	assert.True(t, s.ConnectionConfig.InsecureSkipVerify)
+	assert.Equal(t, "weknora", s.IndexConfig.IndexName)
+}
+
+// TestBuildEnvVectorStores_OpenSearch_InsecureDefaultsFalse verifies the TLS
+// skip flag is false unless the env var is explicitly "true".
+func TestBuildEnvVectorStores_OpenSearch_InsecureDefaultsFalse(t *testing.T) {
+	lookup := mockEnvLookup(map[string]string{"OPENSEARCH_ADDR": "https://os:9200"})
+	stores := BuildEnvVectorStores("opensearch", lookup)
+	require.Len(t, stores, 1)
+	assert.False(t, stores[0].ConnectionConfig.InsecureSkipVerify)
+}
+
+// TestRetrieverEngineMapping_OpenSearch verifies the RETRIEVE_DRIVER mapping.
+func TestRetrieverEngineMapping_OpenSearch(t *testing.T) {
+	m := GetRetrieverEngineMapping()
+	params, ok := m["opensearch"]
+	require.True(t, ok, `retrieverEngineMapping missing "opensearch"`)
+	require.Len(t, params, 2)
+
+	var hasKeywords, hasVector bool
+	for _, p := range params {
+		assert.Equal(t, OpenSearchRetrieverEngineType, p.RetrieverEngineType)
+		switch p.RetrieverType {
+		case KeywordsRetrieverType:
+			hasKeywords = true
+		case VectorRetrieverType:
+			hasVector = true
+		}
+	}
+	assert.True(t, hasKeywords && hasVector, "expected both Keywords and Vector retriever types")
+}
diff --git a/internal/types/vectorstore_test.go b/internal/types/vectorstore_test.go
index 5e018a15..ff66c424 100644
--- a/internal/types/vectorstore_test.go
+++ b/internal/types/vectorstore_test.go
@@ -246,7 +246,7 @@ func TestGetVectorStoreTypes(t *testing.T) {
 	types := GetVectorStoreTypes()
 
 	t.Run("returns supported external engine types (excludes postgres and sqlite)", func(t *testing.T) {
-		assert.Len(t, types, 6)
+		assert.Len(t, types, 7)
 	})
 
 	t.Run("type names match engine constants", func(t *testing.T) {
@@ -260,6 +260,7 @@ func TestGetVectorStoreTypes(t *testing.T) {
 		assert.Contains(t, typeNames, "tencent_vectordb")
 		assert.Contains(t, typeNames, "weaviate")
 		assert.Contains(t, typeNames, "doris")
+		assert.Contains(t, typeNames, "opensearch")
 		assert.NotContains(t, typeNames, "postgres")
 		assert.NotContains(t, typeNames, "sqlite")
 	})
@@ -399,9 +400,10 @@ func TestIsValidEngineType(t *testing.T) {
 	// GetVectorStoreTypes does not list them, Validate rejects them, and
 	// env stores reach the engine registry through BuildEnvVectorStores
 	// instead of through CreateStore.
+	// Note: opensearch is now a VALID DB-store engine (activated in this PR);
+	// see TestIsValidEngineType_OpenSearch in vectorstore_opensearch_test.go.
 	invalidTypes := []RetrieverEngineType{
 		"unknown",
-		"opensearch",
 		"",
 		PostgresRetrieverEngineType,
 		SQLiteRetrieverEngineType,
@@ -1350,64 +1352,3 @@ func TestOpenSearchRetrieverEngineType_DistinctFromExisting(t *testing.T) {
 			"OpenSearch wire value must not collide with %s", e)
 	}
 }
-
-// TestOpenSearchRetrieverEngineType_NotInValidEngineTypes verifies
-// that PR 1 does NOT add the new engine type to validEngineTypes —
-// this is the gate that keeps OpenSearch VectorStore registration
-// rejected until activation lands in a later PR.
-func TestOpenSearchRetrieverEngineType_NotInValidEngineTypes(t *testing.T) {
-	assert.False(t, IsValidEngineType(OpenSearchRetrieverEngineType),
-		"OpenSearch must remain invalid for VectorStore registration "+
-			"until activation lands in a later PR (gated activation)")
-}
-
-// The next three tests are defense-in-depth companions to
-// TestOpenSearchRetrieverEngineType_NotInValidEngineTypes. Each pins
-// a separate activation surface that must remain closed in PR 1 (and
-// in PR 2). Activation lands together with a coordinated flip in
-// PR 3, at which point each of these `assert.False` / `assert.NotContains`
-// / `assert.Nil` lines flips to its positive counterpart in the same
-// diff — the test suite becomes the activation checklist.
-
-// TestRetrieverEngineMapping_OpenSearchNotRegistered pins that
-// `retrieverEngineMapping` does not have an `"opensearch"` key. Without
-// this entry, setting `RETRIEVE_DRIVER=opensearch` is a silent no-op
-// (GetDefaultRetrieverEngines drops the unknown driver from its loop
-// at tenant.go).
-func TestRetrieverEngineMapping_OpenSearchNotRegistered(t *testing.T) {
-	mapping := GetRetrieverEngineMapping()
-	_, ok := mapping["opensearch"]
-	assert.False(t, ok,
-		"retrieverEngineMapping must not register opensearch until "+
-			"activation lands in a later PR (gated activation)")
-}
-
-// TestGetVectorStoreTypes_OmitsOpenSearch pins that the
-// /api/v1/vector-stores/types response does NOT list opensearch.
-// Without this entry, the UI dropdown cannot offer OpenSearch as a
-// store type even if a frontend renderer accidentally tries.
-func TestGetVectorStoreTypes_OmitsOpenSearch(t *testing.T) {
-	listed := GetVectorStoreTypes()
-	for _, info := range listed {
-		assert.NotEqual(t, "opensearch", info.Type,
-			"GetVectorStoreTypes must not surface opensearch until "+
-				"activation lands in a later PR (gated activation)")
-	}
-}
-
-// TestBuildEnvVectorStores_OpenSearchSkipped pins that
-// `BuildEnvVectorStores("opensearch", lookup)` returns nil — the
-// `default:` arm of `buildEnvStoreForDriver`. Without an explicit
-// `case "opensearch":` arm, container.go cannot synthesize an env
-// store for the driver, completing the third lock on the activation
-// chain.
-func TestBuildEnvVectorStores_OpenSearchSkipped(t *testing.T) {
-	stores := BuildEnvVectorStores("opensearch", mockEnvLookup(map[string]string{
-		"OPENSEARCH_ADDR":     "https://os:9200",
-		"OPENSEARCH_USERNAME": "admin",
-	}))
-	assert.Empty(t, stores,
-		"BuildEnvVectorStores must not synthesize an env store for "+
-			"opensearch until activation lands in a later PR (gated "+
-			"activation)")
-}