diff --git a/.changeset/spicy-hairs-watch.md b/.changeset/spicy-hairs-watch.md
new file mode 100644
index 00000000..ca7161f4
--- /dev/null
+++ b/.changeset/spicy-hairs-watch.md
@@ -0,0 +1,6 @@
+---
+"@repo/sandbox-container": patch
+"@cloudflare/sandbox": patch
+---
+
+feat: Add version sync detection between npm package and Docker image
diff --git a/.github/changeset-version.ts b/.github/changeset-version.ts
index 3297f960..ff5737a3 100644
--- a/.github/changeset-version.ts
+++ b/.github/changeset-version.ts
@@ -23,6 +23,12 @@ try {
 
   // Patterns to match version references in different contexts
   const versionPatterns = [
+    // SDK version constant
+    {
+      pattern: /export const SDK_VERSION = '[\d.]+';/g,
+      replacement: `export const SDK_VERSION = '${newVersion}';`,
+      description: "SDK version constant in version.ts",
+    },
     // Docker image versions (production and test)
     {
       pattern: /FROM docker\.io\/cloudflare\/sandbox:[\d.]+/g,
diff --git a/packages/sandbox-container/src/handlers/misc-handler.ts b/packages/sandbox-container/src/handlers/misc-handler.ts
index c227374e..4f8aa012 100644
--- a/packages/sandbox-container/src/handlers/misc-handler.ts
+++ b/packages/sandbox-container/src/handlers/misc-handler.ts
@@ -18,6 +18,8 @@ export class MiscHandler extends BaseHandler<Request, Response> {
         return await this.handleHealth(request, context);
       case '/api/shutdown':
         return await this.handleShutdown(request, context);
+      case '/api/version':
+        return await this.handleVersion(request, context);
       default:
         return this.createErrorResponse({
           message: 'Invalid endpoint',
@@ -54,4 +56,16 @@ export class MiscHandler extends BaseHandler<Request, Response> {
 
     return this.createTypedResponse(response, context);
   }
+
+  private async handleVersion(request: Request, context: RequestContext): Promise<Response> {
+    const version = process.env.SANDBOX_VERSION || 'unknown';
+
+    const response = {
+      success: true,
+      version,
+      timestamp: new Date().toISOString(),
+    };
+
+    return this.createTypedResponse(response, context);
+  }
 }
\ No newline at end of file
diff --git a/packages/sandbox-container/src/routes/setup.ts b/packages/sandbox-container/src/routes/setup.ts
index 056c226d..ce2af8ea 100644
--- a/packages/sandbox-container/src/routes/setup.ts
+++ b/packages/sandbox-container/src/routes/setup.ts
@@ -256,4 +256,11 @@ 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/version',
+    handler: async (req, ctx) => container.get('miscHandler').handle(req, ctx),
+    middleware: [container.get('loggingMiddleware')],
+  });
 }
\ No newline at end of file
diff --git a/packages/sandbox-container/tests/handlers/misc-handler.test.ts b/packages/sandbox-container/tests/handlers/misc-handler.test.ts
index adbf3cac..d0212388 100644
--- a/packages/sandbox-container/tests/handlers/misc-handler.test.ts
+++ b/packages/sandbox-container/tests/handlers/misc-handler.test.ts
@@ -150,6 +150,57 @@ describe('MiscHandler', () => {
     });
   });
 
+  describe('handleVersion - GET /api/version', () => {
+    it('should return version from environment variable', async () => {
+      // Set environment variable for test
+      process.env.SANDBOX_VERSION = '1.2.3';
+
+      const request = new Request('http://localhost:3000/api/version', {
+        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();
+      expect(responseData.success).toBe(true);
+      expect(responseData.version).toBe('1.2.3');
+      expect(responseData.timestamp).toBeDefined();
+      expect(responseData.timestamp).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/);
+    });
+
+    it('should return "unknown" when SANDBOX_VERSION is not set', async () => {
+      // Clear environment variable
+      delete process.env.SANDBOX_VERSION;
+
+      const request = new Request('http://localhost:3000/api/version', {
+        method: 'GET'
+      });
+
+      const response = await miscHandler.handle(request, mockContext);
+
+      expect(response.status).toBe(200);
+      const responseData = await response.json();
+      expect(responseData.version).toBe('unknown');
+    });
+
+    it('should include CORS headers in version response', async () => {
+      process.env.SANDBOX_VERSION = '1.0.0';
+
+      const request = new Request('http://localhost:3000/api/version', {
+        method: 'GET'
+      });
+
+      const response = await miscHandler.handle(request, mockContext);
+
+      expect(response.headers.get('Access-Control-Allow-Origin')).toBe('*');
+      expect(response.headers.get('Access-Control-Allow-Methods')).toBe('GET, POST, OPTIONS');
+      expect(response.headers.get('Access-Control-Allow-Headers')).toBe('Content-Type');
+    });
+  });
+
   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/Dockerfile b/packages/sandbox/Dockerfile
index 3fe70c9c..67a1de8d 100644
--- a/packages/sandbox/Dockerfile
+++ b/packages/sandbox/Dockerfile
@@ -60,9 +60,15 @@ RUN npm ci --production
 # ============================================================================
 FROM ubuntu:22.04 AS runtime
 
+# Accept version as build argument (passed from npm_package_version)
+ARG SANDBOX_VERSION=unknown
+
 # Prevent interactive prompts during package installation
 ENV DEBIAN_FRONTEND=noninteractive
 
+# Set the sandbox version as an environment variable for version checking
+ENV SANDBOX_VERSION=${SANDBOX_VERSION}
+
 # Install essential runtime packages
 RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
diff --git a/packages/sandbox/package.json b/packages/sandbox/package.json
index cfde9fd4..8c30e1a3 100644
--- a/packages/sandbox/package.json
+++ b/packages/sandbox/package.json
@@ -24,9 +24,9 @@
     "check": "biome check && npm run typecheck",
     "fix": "biome check --fix && npm run typecheck",
     "typecheck": "tsc --noEmit",
-    "docker:local": "cd ../.. && docker build -f packages/sandbox/Dockerfile -t cloudflare/sandbox-test:$npm_package_version .",
-    "docker:publish": "cd ../.. && docker buildx build --platform linux/amd64,linux/arm64 -f packages/sandbox/Dockerfile -t cloudflare/sandbox:$npm_package_version --push .",
-    "docker:publish:beta": "cd ../.. && docker buildx build --platform linux/amd64,linux/arm64 -f packages/sandbox/Dockerfile -t cloudflare/sandbox:$npm_package_version-beta --push .",
+    "docker:local": "cd ../.. && docker build -f packages/sandbox/Dockerfile --build-arg SANDBOX_VERSION=$npm_package_version -t cloudflare/sandbox-test:$npm_package_version .",
+    "docker:publish": "cd ../.. && docker buildx build --platform linux/amd64,linux/arm64 -f packages/sandbox/Dockerfile --build-arg SANDBOX_VERSION=$npm_package_version -t cloudflare/sandbox:$npm_package_version --push .",
+    "docker:publish:beta": "cd ../.. && docker buildx build --platform linux/amd64,linux/arm64 -f packages/sandbox/Dockerfile --build-arg SANDBOX_VERSION=$npm_package_version -t cloudflare/sandbox:$npm_package_version-beta --push .",
     "test": "vitest run --config vitest.config.ts",
     "test:e2e": "cd ../.. && vitest run --config vitest.e2e.config.ts \"$@\""
   },
diff --git a/packages/sandbox/src/clients/index.ts b/packages/sandbox/src/clients/index.ts
index e09c90ba..9c4c2cfe 100644
--- a/packages/sandbox/src/clients/index.ts
+++ b/packages/sandbox/src/clients/index.ts
@@ -59,5 +59,6 @@ export type {
 export type {
   CommandsResponse,
   PingResponse,
+  VersionResponse,
 } from './utility-client';
 export { UtilityClient } from './utility-client';
\ No newline at end of file
diff --git a/packages/sandbox/src/clients/utility-client.ts b/packages/sandbox/src/clients/utility-client.ts
index 417c0827..171e6fba 100644
--- a/packages/sandbox/src/clients/utility-client.ts
+++ b/packages/sandbox/src/clients/utility-client.ts
@@ -17,6 +17,13 @@ export interface CommandsResponse extends BaseApiResponse {
   count: number;
 }
 
+/**
+ * Response interface for getting container version
+ */
+export interface VersionResponse extends BaseApiResponse {
+  version: string;
+}
+
 /**
  * Request interface for creating sessions
  */
@@ -91,4 +98,22 @@ export class UtilityClient extends BaseHttpClient {
       throw error;
     }
   }
+
+  /**
+   * Get the container version
+   * Returns the version embedded in the Docker image during build
+   */
+  async getVersion(): Promise<string> {
+    try {
+      const response = await this.get<VersionResponse>('/api/version');
+
+      this.logSuccess('Version retrieved', response.version);
+      return response.version;
+    } catch (error) {
+      // If version endpoint doesn't exist (old container), return 'unknown'
+      // This allows for backward compatibility
+      this.logger.debug('Failed to get container version (may be old container)', { error });
+      return 'unknown';
+    }
+  }
 }
\ No newline at end of file
diff --git a/packages/sandbox/src/sandbox.ts b/packages/sandbox/src/sandbox.ts
index f2ec2534..86b0f4d8 100644
--- a/packages/sandbox/src/sandbox.ts
+++ b/packages/sandbox/src/sandbox.ts
@@ -29,6 +29,7 @@ import {
   validatePort
 } from "./security";
 import { parseSSEStream } from "./sse-parser";
+import { SDK_VERSION } from "./version";
 
 export function getSandbox(
   ns: DurableObjectNamespace<Sandbox>,
@@ -161,6 +162,54 @@ export class Sandbox<Env = unknown> extends Container<Env> implements ISandbox {
 
   override onStart() {
     this.logger.debug('Sandbox started');
+
+    // Check version compatibility asynchronously (don't block startup)
+    this.checkVersionCompatibility().catch(error => {
+      this.logger.error('Version compatibility check failed', error instanceof Error ? error : new Error(String(error)));
+    });
+  }
+
+  /**
+   * Check if the container version matches the SDK version
+   * Logs a warning if there's a mismatch
+   */
+  private async checkVersionCompatibility(): Promise<void> {
+    try {
+      // Get the SDK version (imported from version.ts)
+      const sdkVersion = SDK_VERSION;
+
+      // Get container version
+      const containerVersion = await this.client.utils.getVersion();
+
+      // If container version is unknown, it's likely an old container without the endpoint
+      if (containerVersion === 'unknown') {
+        this.logger.warn(
+          'Container version check: Container version could not be determined. ' +
+          'This may indicate an outdated container image. ' +
+          'Please update your container to match SDK version ' + sdkVersion
+        );
+        return;
+      }
+
+      // Check if versions match
+      if (containerVersion !== sdkVersion) {
+        const message =
+          `Version mismatch detected! SDK version (${sdkVersion}) does not match ` +
+          `container version (${containerVersion}). This may cause compatibility issues. ` +
+          `Please update your container image to version ${sdkVersion}`;
+
+        // Log warning - we can't reliably detect dev vs prod environment in Durable Objects
+        // so we always use warning level as requested by the user
+        this.logger.warn(message);
+      } else {
+        this.logger.debug('Version check passed', { sdkVersion, containerVersion });
+      }
+    } catch (error) {
+      // Don't fail the sandbox initialization if version check fails
+      this.logger.debug('Version compatibility check encountered an error', {
+        error: error instanceof Error ? error.message : String(error)
+      });
+    }
   }
 
   override onStop() {
diff --git a/packages/sandbox/src/version.ts b/packages/sandbox/src/version.ts
new file mode 100644
index 00000000..d7db4c0b
--- /dev/null
+++ b/packages/sandbox/src/version.ts
@@ -0,0 +1,6 @@
+/**
+ * SDK version - automatically synchronized with package.json by Changesets
+ * This file is auto-updated by .github/changeset-version.ts during releases
+ * DO NOT EDIT MANUALLY - Changes will be overwritten on the next version bump
+ */
+export const SDK_VERSION = '0.4.5';
diff --git a/packages/sandbox/tests/utility-client.test.ts b/packages/sandbox/tests/utility-client.test.ts
index e38ef2ec..6e59a95d 100644
--- a/packages/sandbox/tests/utility-client.test.ts
+++ b/packages/sandbox/tests/utility-client.test.ts
@@ -1,7 +1,8 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import type {
   CommandsResponse,
-  PingResponse
+  PingResponse,
+  VersionResponse
 } from '../src/clients';
 import { UtilityClient } from '../src/clients/utility-client';
 import {
@@ -25,6 +26,13 @@ const mockCommandsResponse = (commands: string[], overrides: Partial<CommandsRes
   ...overrides
 });
 
+const mockVersionResponse = (version: string = '0.4.5', overrides: Partial<VersionResponse> = {}): VersionResponse => ({
+  success: true,
+  version,
+  timestamp: '2023-01-01T00:00:00Z',
+  ...overrides
+});
+
 describe('UtilityClient', () => {
   let client: UtilityClient;
   let mockFetch: ReturnType<typeof vi.fn>;
@@ -249,6 +257,64 @@ describe('UtilityClient', () => {
     });
   });
 
+  describe('version checking', () => {
+    it('should get container version successfully', async () => {
+      mockFetch.mockResolvedValue(new Response(
+        JSON.stringify(mockVersionResponse('0.4.5')),
+        { status: 200 }
+      ));
+
+      const result = await client.getVersion();
+
+      expect(result).toBe('0.4.5');
+    });
+
+    it('should handle different version formats', async () => {
+      const versions = ['1.0.0', '2.5.3-beta', '0.0.1', '10.20.30'];
+
+      for (const version of versions) {
+        mockFetch.mockResolvedValueOnce(new Response(
+          JSON.stringify(mockVersionResponse(version)),
+          { status: 200 }
+        ));
+
+        const result = await client.getVersion();
+        expect(result).toBe(version);
+      }
+    });
+
+    it('should return "unknown" when version endpoint does not exist (backward compatibility)', async () => {
+      // Simulate 404 or other error for old containers
+      mockFetch.mockResolvedValue(new Response(
+        JSON.stringify({ error: 'Not Found' }),
+        { status: 404 }
+      ));
+
+      const result = await client.getVersion();
+
+      expect(result).toBe('unknown');
+    });
+
+    it('should return "unknown" on network failure (backward compatibility)', async () => {
+      mockFetch.mockRejectedValue(new Error('Network connection failed'));
+
+      const result = await client.getVersion();
+
+      expect(result).toBe('unknown');
+    });
+
+    it('should handle version response with unknown value', async () => {
+      mockFetch.mockResolvedValue(new Response(
+        JSON.stringify(mockVersionResponse('unknown')),
+        { status: 200 }
+      ));
+
+      const result = await client.getVersion();
+
+      expect(result).toBe('unknown');
+    });
+  });
+
   describe('constructor options', () => {
     it('should initialize with minimal options', () => {
       const minimalClient = new UtilityClient();
diff --git a/packages/sandbox/tests/version.test.ts b/packages/sandbox/tests/version.test.ts
new file mode 100644
index 00000000..81374777
--- /dev/null
+++ b/packages/sandbox/tests/version.test.ts
@@ -0,0 +1,16 @@
+import { describe, expect, test } from 'vitest';
+import packageJson from '../package.json';
+import { SDK_VERSION } from '../src/version';
+
+describe('Version Sync', () => {
+  test('SDK_VERSION matches package.json version', () => {
+    // Verify versions match
+    expect(SDK_VERSION).toBe(packageJson.version);
+  });
+
+  test('SDK_VERSION is a valid semver version', () => {
+    // Check if version matches semver pattern (major.minor.patch)
+    const semverPattern = /^\d+\.\d+\.\d+(-[\w.]+)?$/;
+    expect(SDK_VERSION).toMatch(semverPattern);
+  });
+});