diff --git a/.changeset/runtime-identity-api.md b/.changeset/runtime-identity-api.md
new file mode 100644
index 000000000..32ddff624
--- /dev/null
+++ b/.changeset/runtime-identity-api.md
@@ -0,0 +1,8 @@
+---
+'@cloudflare/sandbox': patch
+---
+
+Add `getRuntimeIdentity()` to detect when a sandbox starts a new
+container runtime. Use the returned `runtimeId` to compare the current
+runtime with the last one you observed and decide when reconciliation
+is needed.
diff --git a/packages/sandbox-container/src/handlers/misc-handler.ts b/packages/sandbox-container/src/handlers/misc-handler.ts
index aa9a72383..26f4930f5 100644
--- a/packages/sandbox-container/src/handlers/misc-handler.ts
+++ b/packages/sandbox-container/src/handlers/misc-handler.ts
@@ -11,6 +11,16 @@ export interface VersionResult {
   timestamp: string;
 }
 
+export interface RuntimeIdentityResult {
+  success: boolean;
+  runtimeId: string;
+  startedAt: string;
+  timestamp: string;
+}
+
+const CONTAINER_RUNTIME_ID = crypto.randomUUID();
+const CONTAINER_STARTED_AT = new Date().toISOString();
+
 export class MiscHandler extends BaseHandler<Request, Response> {
   async handle(request: Request, context: RequestContext): Promise<Response> {
     const url = new URL(request.url);
@@ -27,6 +37,8 @@ export class MiscHandler extends BaseHandler<Request, Response> {
         return await this.handleShutdown(request, context);
       case '/api/version':
         return await this.handleVersion(request, context);
+      case '/api/runtime':
+        return await this.handleRuntime(request, context);
       default:
         return this.createErrorResponse(
           {
@@ -90,4 +102,18 @@ export class MiscHandler extends BaseHandler<Request, Response> {
 
     return this.createTypedResponse(response, context);
   }
+
+  private async handleRuntime(
+    request: Request,
+    context: RequestContext
+  ): Promise<Response> {
+    const response: RuntimeIdentityResult = {
+      success: true,
+      runtimeId: CONTAINER_RUNTIME_ID,
+      startedAt: CONTAINER_STARTED_AT,
+      timestamp: new Date().toISOString()
+    };
+
+    return this.createTypedResponse(response, context);
+  }
 }
diff --git a/packages/sandbox-container/src/routes/setup.ts b/packages/sandbox-container/src/routes/setup.ts
index c8bfc5c6d..206663ce4 100644
--- a/packages/sandbox-container/src/routes/setup.ts
+++ b/packages/sandbox-container/src/routes/setup.ts
@@ -478,4 +478,11 @@ export function setupRoutes(router: Router, container: Container): void {
     handler: async (req, ctx) => container.get('miscHandler').handle(req, ctx),
     middleware: [container.get('loggingMiddleware')]
   });
+
+  router.register({
+    method: 'GET',
+    path: '/api/runtime',
+    handler: async (req, ctx) => container.get('miscHandler').handle(req, ctx),
+    middleware: [container.get('loggingMiddleware')]
+  });
 }
diff --git a/packages/sandbox-container/tests/handlers/misc-handler.test.ts b/packages/sandbox-container/tests/handlers/misc-handler.test.ts
index e7d923b05..53a2d8233 100644
--- a/packages/sandbox-container/tests/handlers/misc-handler.test.ts
+++ b/packages/sandbox-container/tests/handlers/misc-handler.test.ts
@@ -4,6 +4,7 @@ import type { ErrorResponse } from '@repo/shared/errors';
 import type { RequestContext } from '@sandbox-container/core/types';
 import {
   MiscHandler,
+  type RuntimeIdentityResult,
   type VersionResult
 } from '@sandbox-container/handlers/misc-handler';
 
@@ -224,6 +225,48 @@ describe('MiscHandler', () => {
     });
   });
 
+  describe('handleRuntime - GET /api/runtime', () => {
+    it('should return runtime identity', async () => {
+      const request = new Request('http://localhost:3000/api/runtime', {
+        method: 'GET'
+      });
+
+      const response = await miscHandler.handle(request, mockContext);
+
+      expect(response.status).toBe(200);
+      expect(response.headers.get('Content-Type')).toBe('application/json');
+
+      const responseData = (await response.json()) as RuntimeIdentityResult;
+      expect(responseData.success).toBe(true);
+      expect(responseData.runtimeId).toMatch(
+        /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i
+      );
+      expect(responseData.startedAt).toMatch(
+        /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/
+      );
+      expect(responseData.timestamp).toMatch(
+        /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/
+      );
+    });
+
+    it('should keep runtime identity stable across requests', async () => {
+      const request = new Request('http://localhost:3000/api/runtime', {
+        method: 'GET'
+      });
+
+      const response1 = await miscHandler.handle(request, mockContext);
+      await new Promise((resolve) => setTimeout(resolve, 5));
+      const response2 = await miscHandler.handle(request, mockContext);
+
+      const responseData1 = (await response1.json()) as RuntimeIdentityResult;
+      const responseData2 = (await response2.json()) as RuntimeIdentityResult;
+
+      expect(responseData1.runtimeId).toBe(responseData2.runtimeId);
+      expect(responseData1.startedAt).toBe(responseData2.startedAt);
+      expect(responseData1.timestamp).not.toBe(responseData2.timestamp);
+    });
+  });
+
   describe('handleShutdown - POST /api/shutdown', () => {
     it('should return shutdown response with JSON content type', async () => {
       const request = new Request('http://localhost:3000/api/shutdown', {
diff --git a/packages/sandbox/src/clients/utility-client.ts b/packages/sandbox/src/clients/utility-client.ts
index dfe4df238..c4843efe3 100644
--- a/packages/sandbox/src/clients/utility-client.ts
+++ b/packages/sandbox/src/clients/utility-client.ts
@@ -1,3 +1,5 @@
+import type { RuntimeIdentity } from '@repo/shared';
+import { createErrorFromResponse, ErrorCode, SandboxError } from '../errors';
 import { BaseHttpClient } from './base-client';
 import type { BaseApiResponse, HttpClientOptions } from './types';
 
@@ -24,6 +26,11 @@ export interface VersionResponse extends BaseApiResponse {
   version: string;
 }
 
+/**
+ * Response interface for getting container runtime identity
+ */
+interface RuntimeIdentityResponse extends BaseApiResponse, RuntimeIdentity {}
+
 /**
  * Request interface for creating sessions
  */
@@ -141,4 +148,36 @@ export class UtilityClient extends BaseHttpClient {
       return 'unknown';
     }
   }
+
+  /**
+   * Get the current container runtime identity.
+   * `runtimeId` changes when the underlying container boots again.
+   */
+  async getRuntimeIdentity(): Promise<RuntimeIdentity> {
+    try {
+      const response = await this.get<RuntimeIdentityResponse>('/api/runtime');
+
+      return {
+        runtimeId: response.runtimeId,
+        startedAt: response.startedAt
+      };
+    } catch (error) {
+      if (error instanceof SandboxError && error.httpStatus === 404) {
+        throw createErrorFromResponse({
+          code: ErrorCode.UNKNOWN_ERROR,
+          message:
+            'Runtime identity is not supported by this sandbox container. Recreate the sandbox or upgrade to a newer container image.',
+          context: {
+            endpoint: '/api/runtime'
+          },
+          httpStatus: 404,
+          timestamp: new Date().toISOString(),
+          suggestion:
+            'Recreate the sandbox or upgrade to a newer container image before calling getRuntimeIdentity().'
+        });
+      }
+
+      throw error;
+    }
+  }
 }
diff --git a/packages/sandbox/src/index.ts b/packages/sandbox/src/index.ts
index 0e818df66..e42ab28fc 100644
--- a/packages/sandbox/src/index.ts
+++ b/packages/sandbox/src/index.ts
@@ -52,6 +52,7 @@ export type {
   RemoteMountBucketOptions,
   RestoreBackupResult,
   RunCodeOptions,
+  RuntimeIdentity,
   SandboxOptions,
   SessionOptions,
   StreamOptions,
diff --git a/packages/sandbox/src/sandbox.ts b/packages/sandbox/src/sandbox.ts
index ab91f93b9..3e54e2cee 100644
--- a/packages/sandbox/src/sandbox.ts
+++ b/packages/sandbox/src/sandbox.ts
@@ -25,6 +25,7 @@ import type {
   RemoteMountBucketOptions,
   RestoreBackupResult,
   RunCodeOptions,
+  RuntimeIdentity,
   SandboxOptions,
   SessionOptions,
   StreamOptions,
@@ -2986,6 +2987,10 @@ export class Sandbox<Env = unknown> extends Container<Env> implements ISandbox {
     });
   }
 
+  async getRuntimeIdentity(): Promise<RuntimeIdentity> {
+    return await this.client.utils.getRuntimeIdentity();
+  }
+
   /**
    * Expose a port and get a preview URL for accessing services running in the sandbox
    *
diff --git a/packages/sandbox/tests/sandbox.test.ts b/packages/sandbox/tests/sandbox.test.ts
index bfd861103..05678a209 100644
--- a/packages/sandbox/tests/sandbox.test.ts
+++ b/packages/sandbox/tests/sandbox.test.ts
@@ -218,6 +218,20 @@ describe('Sandbox - Automatic Session Management', () => {
       });
     });
 
+    it('should return runtime identity from the utility client', async () => {
+      vi.spyOn(sandbox.client.utils, 'getRuntimeIdentity').mockResolvedValue({
+        runtimeId: 'rt-1',
+        startedAt: '2026-04-07T00:00:00.000Z'
+      });
+
+      const result = await sandbox.getRuntimeIdentity();
+
+      expect(result).toEqual({
+        runtimeId: 'rt-1',
+        startedAt: '2026-04-07T00:00:00.000Z'
+      });
+    });
+
     it('should reuse default session across multiple operations', async () => {
       await sandbox.exec('echo test1');
       await sandbox.writeFile('/test.txt', 'content');
diff --git a/packages/sandbox/tests/utility-client.test.ts b/packages/sandbox/tests/utility-client.test.ts
index 20f6196f1..3d3ae2d14 100644
--- a/packages/sandbox/tests/utility-client.test.ts
+++ b/packages/sandbox/tests/utility-client.test.ts
@@ -39,6 +39,21 @@ const mockVersionResponse = (
   ...overrides
 });
 
+const mockRuntimeIdentityResponse = (
+  overrides: Partial<{
+    success: boolean;
+    runtimeId: string;
+    startedAt: string;
+    timestamp: string;
+  }> = {}
+) => ({
+  success: true,
+  runtimeId: 'rt-123',
+  startedAt: '2023-01-01T00:00:00Z',
+  timestamp: '2023-01-01T00:00:01Z',
+  ...overrides
+});
+
 describe('UtilityClient', () => {
   let client: UtilityClient;
   let mockFetch: ReturnType<typeof vi.fn>;
@@ -324,6 +339,54 @@ describe('UtilityClient', () => {
     });
   });
 
+  describe('runtime identity', () => {
+    it('should get runtime identity successfully', async () => {
+      mockFetch.mockResolvedValue(
+        new Response(JSON.stringify(mockRuntimeIdentityResponse()), {
+          status: 200
+        })
+      );
+
+      const result = await client.getRuntimeIdentity();
+
+      expect(result).toEqual({
+        runtimeId: 'rt-123',
+        startedAt: '2023-01-01T00:00:00Z'
+      });
+    });
+
+    it('should request the runtime endpoint', async () => {
+      mockFetch.mockResolvedValue(
+        new Response(JSON.stringify(mockRuntimeIdentityResponse()), {
+          status: 200
+        })
+      );
+
+      await client.getRuntimeIdentity();
+
+      expect(mockFetch).toHaveBeenCalledWith(
+        'http://test.com/api/runtime',
+        expect.objectContaining({ method: 'GET' })
+      );
+    });
+
+    it('should surface runtime endpoint failures', async () => {
+      mockFetch.mockResolvedValue(
+        new Response(JSON.stringify({ error: 'Not Found' }), { status: 404 })
+      );
+
+      await expect(client.getRuntimeIdentity()).rejects.toThrow();
+    });
+
+    it('should throw an explicit compatibility error for missing endpoint', async () => {
+      mockFetch.mockResolvedValue(new Response('Not Found', { status: 404 }));
+
+      await expect(client.getRuntimeIdentity()).rejects.toThrow(
+        'Runtime identity is not supported by this sandbox container. Recreate the sandbox or upgrade to a newer container image.'
+      );
+    });
+  });
+
   describe('constructor options', () => {
     it('should initialize with minimal options', () => {
       const minimalClient = new UtilityClient();
diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
index 103f75bb8..2c5d9f315 100644
--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -172,6 +172,7 @@ export type {
   RemoteMountBucketOptions,
   RenameFileResult,
   RestoreBackupResult,
+  RuntimeIdentity,
   // Sandbox configuration options
   SandboxOptions,
   // Session management result types
diff --git a/packages/shared/src/types.ts b/packages/shared/src/types.ts
index 2e3be370e..e5055d6c3 100644
--- a/packages/shared/src/types.ts
+++ b/packages/shared/src/types.ts
@@ -1071,6 +1071,18 @@ export interface ExecutionSession {
   terminal(request: Request, options?: PtyOptions): Promise<Response>;
 }
 
+/**
+ * Identity for a single container runtime.
+ *
+ * `runtimeId` changes whenever the underlying container boots again.
+ */
+export interface RuntimeIdentity {
+  /** Unique identifier for the current container boot. */
+  runtimeId: string;
+  /** When the current container boot started. */
+  startedAt: string;
+}
+
 // Backup types
 /**
  * Options for creating a directory backup
@@ -1333,6 +1345,9 @@ export interface ISandbox {
   createBackup(options: BackupOptions): Promise<DirectoryBackup>;
   restoreBackup(backup: DirectoryBackup): Promise<RestoreBackupResult>;
 
+  // Runtime lifecycle metadata
+  getRuntimeIdentity(): Promise<RuntimeIdentity>;
+
   // WebSocket connection
   wsConnect(request: Request, port: number): Promise<Response>;
 }
diff --git a/tests/e2e/runtime-identity-workflow.test.ts b/tests/e2e/runtime-identity-workflow.test.ts
new file mode 100644
index 000000000..ab98d0968
--- /dev/null
+++ b/tests/e2e/runtime-identity-workflow.test.ts
@@ -0,0 +1,63 @@
+import { afterAll, beforeAll, describe, expect, test } from 'vitest';
+import {
+  cleanupTestSandbox,
+  createTestSandbox,
+  type TestSandbox
+} from './helpers/global-sandbox';
+import type { RuntimeIdentityResponse } from './test-worker/types';
+
+describe('Runtime Identity E2E', () => {
+  let sandbox: TestSandbox | null = null;
+  let workerUrl: string;
+
+  beforeAll(async () => {
+    sandbox = await createTestSandbox();
+    workerUrl = sandbox.workerUrl;
+  }, 120000);
+
+  afterAll(async () => {
+    await cleanupTestSandbox(sandbox);
+    sandbox = null;
+  }, 120000);
+
+  test('should keep identity stable until the sandbox is recreated', async () => {
+    if (!sandbox) {
+      throw new Error('Sandbox was not initialized');
+    }
+
+    const response1 = await fetch(`${workerUrl}/api/runtime/identity`, {
+      method: 'GET',
+      headers: sandbox.headers()
+    });
+    expect(response1.ok).toBe(true);
+
+    const runtime1 = (await response1.json()) as RuntimeIdentityResponse;
+
+    const response2 = await fetch(`${workerUrl}/api/runtime/identity`, {
+      method: 'GET',
+      headers: sandbox.headers()
+    });
+    expect(response2.ok).toBe(true);
+
+    const runtime2 = (await response2.json()) as RuntimeIdentityResponse;
+    expect(runtime2).toEqual(runtime1);
+
+    await cleanupTestSandbox(sandbox);
+
+    const recreateResponse = await fetch(`${workerUrl}/api/execute`, {
+      method: 'POST',
+      headers: sandbox.headers(),
+      body: JSON.stringify({ command: 'echo ready' })
+    });
+    expect(recreateResponse.ok).toBe(true);
+
+    const response3 = await fetch(`${workerUrl}/api/runtime/identity`, {
+      method: 'GET',
+      headers: sandbox.headers()
+    });
+    expect(response3.ok).toBe(true);
+
+    const runtime3 = (await response3.json()) as RuntimeIdentityResponse;
+    expect(runtime3.runtimeId).not.toBe(runtime1.runtimeId);
+  }, 120000);
+});
diff --git a/tests/e2e/test-worker/index.ts b/tests/e2e/test-worker/index.ts
index 2ba86d591..a637c8f5d 100644
--- a/tests/e2e/test-worker/index.ts
+++ b/tests/e2e/test-worker/index.ts
@@ -28,6 +28,7 @@ import type {
   ErrorResponse,
   HealthResponse,
   PortUnexposeResponse,
+  RuntimeIdentityResponse,
   SessionCreateResponse,
   SuccessResponse,
   SuccessWithMessageResponse,
@@ -494,6 +495,18 @@ console.log('Terminal server on port ' + port);
         });
       }
 
+      if (
+        url.pathname === '/api/runtime/identity' &&
+        request.method === 'GET'
+      ) {
+        const runtimeIdentity = await sandbox.getRuntimeIdentity();
+        const response: RuntimeIdentityResponse = runtimeIdentity;
+
+        return new Response(JSON.stringify(response), {
+          headers: { 'Content-Type': 'application/json' }
+        });
+      }
+
       // Command execution
       if (url.pathname === '/api/execute' && request.method === 'POST') {
         const result = await executor.exec(body.command, {
diff --git a/tests/e2e/test-worker/types.ts b/tests/e2e/test-worker/types.ts
index 8a0bce2a6..f504be7fd 100644
--- a/tests/e2e/test-worker/types.ts
+++ b/tests/e2e/test-worker/types.ts
@@ -31,6 +31,11 @@ export interface SuccessWithMessageResponse {
   message: string;
 }
 
+export interface RuntimeIdentityResponse {
+  runtimeId: string;
+  startedAt: string;
+}
+
 // R2 bucket operations
 export interface BucketPutResponse {
   success: boolean;