diff --git a/README.md b/README.md
index c4ec2c1e0..2689fa831 100644
--- a/README.md
+++ b/README.md
@@ -1500,7 +1500,7 @@ Create `~/.agentmemory/.env`:
 
 <h2 id="api"><picture><source media="(prefers-color-scheme: dark)" srcset="assets/tags/light/section-api.svg"><img src="assets/tags/section-api.svg" alt="API" height="32" /></picture></h2>
 
-128 endpoints on port `3111`. The REST API binds to `127.0.0.1` by default. Protected endpoints require `Authorization: Bearer <secret>` when `AGENTMEMORY_SECRET` is set, and mesh sync endpoints require `AGENTMEMORY_SECRET` on both peers.
+129 endpoints on port `3111`. The REST API binds to `127.0.0.1` by default. Protected endpoints require `Authorization: Bearer <secret>` when `AGENTMEMORY_SECRET` is set, and mesh sync endpoints require `AGENTMEMORY_SECRET` on both peers.
 
 <details>
 <summary>Key endpoints</summary>
diff --git a/src/functions/migrate-vector-index.ts b/src/functions/migrate-vector-index.ts
index 058eab84a..208112d65 100644
--- a/src/functions/migrate-vector-index.ts
+++ b/src/functions/migrate-vector-index.ts
@@ -10,6 +10,7 @@ export interface MigrateVectorIndexResult {
   failed: number;
   vectorSize: number;
   failedSessions: string[];
+  index: VectorIndex;
 }
 
 // Validate one embedding's shape against the provider's declared dimensions
@@ -111,7 +112,7 @@ export async function migrateVectorIndex(
     // failedSessions list and can't tell apart "0 sessions, all OK"
     // from "kv.list itself blew up".
     failedSessions.push("<sessions-list-failed>");
-    return { success: false, totalProcessed: processed, failed, vectorSize: newIndex.size, failedSessions };
+    return { success: false, totalProcessed: processed, failed, vectorSize: newIndex.size, failedSessions, index: newIndex };
   }
 
   for (const session of sessions) {
@@ -148,5 +149,6 @@ export async function migrateVectorIndex(
     failed,
     vectorSize: newIndex.size,
     failedSessions,
+    index: newIndex,
   };
 }
diff --git a/src/functions/search.ts b/src/functions/search.ts
index df699a1a3..a133215c2 100644
--- a/src/functions/search.ts
+++ b/src/functions/search.ts
@@ -6,7 +6,9 @@ import { SearchIndex } from '../state/search-index.js'
 import { VectorIndex } from '../state/vector-index.js'
 import type { EmbeddingProvider } from '../types.js'
 import { memoryToObservation } from '../state/memory-utils.js'
+import { migrateVectorIndex } from './migrate-vector-index.js'
 import { recordAccessBatch } from './access-tracker.js'
+import { recordAudit } from './audit.js'
 import { logger } from "../logger.js";
 import { getAgentId, isAgentScopeIsolated } from "../config.js";
 
@@ -319,7 +321,87 @@ export async function rebuildIndex(kv: StateKV): Promise<number> {
   return count
 }
 
+// Re-embed the whole corpus against the active embedding provider and swap
+// the result into the live vector index. Used after switching embedding
+// model/dimensions: the new model produces a different vector space, so old
+// vectors must be recomputed (see the dimension restore guard in index.ts).
+// The new index is built off to the side via migrateVectorIndex so the live
+// index keeps serving during the (possibly long) rebuild, then swapped in
+// place with restoreFrom, since IndexPersistence holds a reference to the live
+// VectorIndex, so replacing the reference would desync persistence. The swap
+// only happens on a fully clean rebuild (failed === 0); on any failure the
+// live index is left untouched and the caller gets failedSessions to retry.
+export async function reindexVectors(kv: StateKV): Promise<{
+  success: boolean
+  swapped: boolean
+  totalProcessed: number
+  failed: number
+  vectorSize: number
+  failedSessions: string[]
+  provider: string | null
+  dimensions: number | null
+  error?: string
+}> {
+  const ep = currentEmbeddingProvider
+  if (!ep) {
+    return {
+      success: false,
+      swapped: false,
+      totalProcessed: 0,
+      failed: 0,
+      vectorSize: 0,
+      failedSessions: [],
+      provider: null,
+      dimensions: null,
+      error:
+        'no embedding provider configured; set EMBEDDING_PROVIDER or a provider API key and restart',
+    }
+  }
+  const vi = vectorIndex
+  if (!vi) {
+    return {
+      success: false,
+      swapped: false,
+      totalProcessed: 0,
+      failed: 0,
+      vectorSize: 0,
+      failedSessions: [],
+      provider: ep.name,
+      dimensions: ep.dimensions,
+      error: 'vector index not initialized',
+    }
+  }
+  const { index, ...stats } = await migrateVectorIndex(kv, ep)
+  let swapped = false
+  if (stats.success) {
+    vi.restoreFrom(index)
+    swapped = true
+    try {
+      await flushIndexSave()
+    } catch (err) {
+      return {
+        ...stats,
+        success: false,
+        swapped,
+        provider: ep.name,
+        dimensions: ep.dimensions,
+        error: `index swapped but persistence failed: ${err instanceof Error ? err.message : String(err)}`,
+      }
+    }
+    await recordAudit(kv, 'vector_index_swap', 'mem::reindex-vectors', [ep.name], {
+      provider: ep.name,
+      dimensions: ep.dimensions,
+      totalProcessed: stats.totalProcessed,
+    })
+  }
+  return { ...stats, swapped, provider: ep.name, dimensions: ep.dimensions }
+}
+
 export function registerSearchFunction(sdk: ISdk, kv: StateKV): void {
+  sdk.registerFunction('mem::reindex-vectors', async () => {
+    return await reindexVectors(kv)
+  })
+
   sdk.registerFunction(
     'mem::search',
     async (data: {
diff --git a/src/index.ts b/src/index.ts
index 4233e8a67..354477ad2 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -518,7 +518,7 @@ async function main() {
     `Ready. ${embeddingProvider ? "Triple-stream (BM25+Vector+Graph)" : "BM25+Graph"} search active.`,
   );
   bootLog(
-    `REST API: 128 endpoints at http://localhost:${config.restPort}/agentmemory/*`,
+    `REST API: 129 endpoints at http://localhost:${config.restPort}/agentmemory/*`,
   );
   bootLog(
     `MCP surface (opt-in via \`npx @agentmemory/mcp\`): ${getAllTools().length} tools · 6 resources · 3 prompts`,
diff --git a/src/triggers/api.ts b/src/triggers/api.ts
index 7b6c2bf2b..2291f3f96 100644
--- a/src/triggers/api.ts
+++ b/src/triggers/api.ts
@@ -1104,6 +1104,23 @@ export function registerApiTriggers(
     config: { api_path: "/agentmemory/migrate", http_method: "POST" },
   });
 
+  sdk.registerFunction("api::reindex-vectors",
+    async (req: ApiRequest<Record<string, unknown>>): Promise<Response> => {
+      const authErr = checkAuth(req, secret);
+      if (authErr) return authErr;
+      const result = await sdk.trigger({
+        function_id: "mem::reindex-vectors",
+        payload: {},
+      });
+      return { status_code: 200, body: result };
+    },
+  );
+  sdk.registerTrigger({
+    type: "http",
+    function_id: "api::reindex-vectors",
+    config: { api_path: "/agentmemory/reindex-vectors", http_method: "POST" },
+  });
+
   sdk.registerFunction("api::evict", 
     async (req: ApiRequest<{ dryRun?: boolean }>): Promise<Response> => {
       const authErr = checkAuth(req, secret);
diff --git a/src/types.ts b/src/types.ts
index 6797dfaf9..361046a25 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -608,7 +608,8 @@ export interface AuditEntry {
     | "slot_replace"
     | "slot_create"
     | "slot_delete"
-    | "slot_reflect";
+    | "slot_reflect"
+    | "vector_index_swap";
   userId?: string;
   functionId: string;
   targetIds: string[];
diff --git a/test/reindex-vectors.test.ts b/test/reindex-vectors.test.ts
new file mode 100644
index 000000000..16c759e35
--- /dev/null
+++ b/test/reindex-vectors.test.ts
@@ -0,0 +1,123 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("../src/logger.js", () => ({
+  logger: { info: vi.fn(), warn: vi.fn(), error: vi.fn() },
+}));
+
+import { VectorIndex } from "../src/state/vector-index.js";
+import {
+  reindexVectors,
+  setVectorIndex,
+  setEmbeddingProvider,
+  getVectorIndex,
+} from "../src/functions/search.js";
+import type { EmbeddingProvider } from "../src/types.js";
+
+const fourDimProvider: EmbeddingProvider = {
+  name: "test-4d",
+  dimensions: 4,
+  embed: async (_text: string) => new Float32Array([0.1, 0.2, 0.3, 0.4]),
+  embedBatch: async (texts: string[]) =>
+    texts.map(() => new Float32Array([0.1, 0.2, 0.3, 0.4])),
+};
+
+function mockKV() {
+  const store = new Map<string, Map<string, unknown>>();
+  return {
+    get: async <T>(scope: string, key: string): Promise<T | null> =>
+      (store.get(scope)?.get(key) as T) ?? null,
+    set: async <T>(scope: string, key: string, data: T): Promise<T> => {
+      if (!store.has(scope)) store.set(scope, new Map());
+      store.get(scope)!.set(key, data);
+      return data;
+    },
+    delete: async (_scope: string, _key: string): Promise<void> => {},
+    list: async <T>(scope: string): Promise<T[]> => {
+      const entries = store.get(scope);
+      return entries ? (Array.from(entries.values()) as T[]) : [];
+    },
+  };
+}
+
+async function seedCorpus(kv: ReturnType<typeof mockKV>) {
+  await kv.set("mem:sessions", "ses_1", { id: "ses_1" });
+  await kv.set("mem:obs:ses_1", "obs_1", {
+    id: "obs_1",
+    sessionId: "ses_1",
+    timestamp: new Date().toISOString(),
+    type: "decision",
+    title: "reindex observation",
+    facts: ["x"],
+    narrative: "to be re-embedded",
+    concepts: [],
+    files: [],
+    importance: 5,
+  });
+  await kv.set("mem:memories", "mem_1", {
+    id: "mem_1",
+    createdAt: new Date().toISOString(),
+    updatedAt: new Date().toISOString(),
+    type: "fact",
+    title: "reindex memory",
+    content: "this memory will be re-embedded",
+    concepts: [],
+    files: [],
+    sessionIds: ["ses_1"],
+    strength: 7,
+    version: 1,
+    isLatest: true,
+  });
+}
+
+describe("reindexVectors", () => {
+  beforeEach(() => {
+    setVectorIndex(null);
+    setEmbeddingProvider(null);
+  });
+
+  it("re-embeds the corpus and swaps it into the live vector index", async () => {
+    const kv = mockKV();
+    await seedCorpus(kv);
+    const live = new VectorIndex();
+    setVectorIndex(live);
+    setEmbeddingProvider(fourDimProvider);
+
+    const result = await reindexVectors(kv as never);
+
+    expect(result.success).toBe(true);
+    expect(result.swapped).toBe(true);
+    expect(result.failed).toBe(0);
+    expect(result.totalProcessed).toBe(2);
+    expect(result.vectorSize).toBe(2);
+    expect(result.provider).toBe("test-4d");
+    expect(result.dimensions).toBe(4);
+    expect(getVectorIndex()!.size).toBe(2);
+  });
+
+  it("returns success:false without swapping when no embedding provider is configured", async () => {
+    const kv = mockKV();
+    await seedCorpus(kv);
+    const live = new VectorIndex();
+    setVectorIndex(live);
+    setEmbeddingProvider(null);
+
+    const result = await reindexVectors(kv as never);
+
+    expect(result.success).toBe(false);
+    expect(result.swapped).toBe(false);
+    expect(result.error).toBeTruthy();
+    expect(getVectorIndex()!.size).toBe(0);
+  });
+
+  it("returns success:false without throwing when the vector index is not initialized", async () => {
+    const kv = mockKV();
+    await seedCorpus(kv);
+    setVectorIndex(null);
+    setEmbeddingProvider(fourDimProvider);
+
+    const result = await reindexVectors(kv as never);
+
+    expect(result.success).toBe(false);
+    expect(result.swapped).toBe(false);
+  });
+});
diff --git a/test/vector-index-dimensions.test.ts b/test/vector-index-dimensions.test.ts
index 140d7f8ae..eadfb433a 100644
--- a/test/vector-index-dimensions.test.ts
+++ b/test/vector-index-dimensions.test.ts
@@ -129,4 +129,26 @@ describe("migrateVectorIndex", () => {
     expect(result.vectorSize).toBe(0);
     expect(result.failed).toBe(0);
   });
+
+  it("returns the rebuilt index so callers can swap it into the live index", async () => {
+    const kv = mockKV();
+    await kv.set("mem:sessions", "ses_1", { id: "ses_1" });
+    await kv.set("mem:obs:ses_1", "obs_1", {
+      id: "obs_1",
+      sessionId: "ses_1",
+      timestamp: new Date().toISOString(),
+      type: "decision",
+      title: "swap test",
+      facts: ["x"],
+      narrative: "to be re-embedded",
+      concepts: [],
+      files: [],
+      importance: 5,
+    });
+
+    const result = await migrateVectorIndex(kv as never, newProvider);
+    expect(result.index).toBeInstanceOf(VectorIndex);
+    expect(result.index.size).toBe(result.vectorSize);
+    expect(result.index.size).toBe(1);
+  });
 });