diff --git a/.changeset/vercel-sandbox-user-agent.md b/.changeset/vercel-sandbox-user-agent.md
new file mode 100644
index 000000000..1af7df9b1
--- /dev/null
+++ b/.changeset/vercel-sandbox-user-agent.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/ai-sandbox-vercel': patch
+---
+
+Vercel sandbox requests now append a `@tanstack/ai` token to the `user-agent`.
diff --git a/packages/ai-sandbox-vercel/src/provider.ts b/packages/ai-sandbox-vercel/src/provider.ts
index b172c0d65..c4da4beeb 100644
--- a/packages/ai-sandbox-vercel/src/provider.ts
+++ b/packages/ai-sandbox-vercel/src/provider.ts
@@ -1,5 +1,6 @@
 import { APIError, Sandbox } from '@vercel/sandbox'
 import { VERCEL_CAPS, VercelHandle } from './handle'
+import { withSandboxUserAgent } from './user-agent'
 import type {
   SandboxCapabilities,
   SandboxCreateInput,
@@ -67,6 +68,8 @@ export function isDirAlreadyExistsError(error: unknown): boolean {
 class VercelProvider implements SandboxProvider {
   readonly name = 'vercel'
 
+  private readonly fetch = withSandboxUserAgent()
+
   constructor(private readonly config: VercelSandboxConfig) {}
 
   capabilities(): SandboxCapabilities {
@@ -101,6 +104,7 @@ class VercelProvider implements SandboxProvider {
   async create(input: SandboxCreateInput): Promise<SandboxHandle> {
     const sandbox = await Sandbox.create({
       ...this.auth(),
+      fetch: this.fetch,
       runtime: this.config.runtime ?? DEFAULT_RUNTIME,
       ...(this.config.timeout !== undefined
         ? { timeout: this.config.timeout }
@@ -133,7 +137,11 @@ class VercelProvider implements SandboxProvider {
 
   async resume(input: SandboxResumeInput): Promise<SandboxHandle | null> {
     try {
-      const sandbox = await Sandbox.get({ name: input.id, ...this.auth() })
+      const sandbox = await Sandbox.get({
+        name: input.id,
+        ...this.auth(),
+        fetch: this.fetch,
+      })
       return new VercelHandle({
         sandbox,
         workdir: this.workdir,
@@ -147,7 +155,11 @@ class VercelProvider implements SandboxProvider {
 
   async destroy(input: SandboxDestroyInput): Promise<void> {
     try {
-      const sandbox = await Sandbox.get({ name: input.id, ...this.auth() })
+      const sandbox = await Sandbox.get({
+        name: input.id,
+        ...this.auth(),
+        fetch: this.fetch,
+      })
       await sandbox.stop()
     } catch {
       // Already stopped / gone.
diff --git a/packages/ai-sandbox-vercel/src/user-agent.ts b/packages/ai-sandbox-vercel/src/user-agent.ts
new file mode 100644
index 000000000..2a96f9077
--- /dev/null
+++ b/packages/ai-sandbox-vercel/src/user-agent.ts
@@ -0,0 +1,33 @@
+/**
+ * User-agent tagging for Vercel Sandbox traffic.
+ *
+ * The `@vercel/sandbox` SDK sends a `user-agent` of
+ * `vercel/sandbox/<sdk-version> (…)` on every API request. We wrap the SDK's
+ * `fetch` so each request also carries a `@tanstack/ai` token.
+ */
+
+export const USER_AGENT_TOKEN = '@tanstack/ai'
+
+/**
+ * Wraps a `fetch` so every request's `user-agent` contains the package name
+ * (e.g. `vercel/sandbox/2.2.1 (…) @tanstack/ai`). When no
+ * `user-agent` is present, the token becomes the whole header.
+ */
+export function withSandboxUserAgent(
+  inner: typeof globalThis.fetch = globalThis.fetch,
+): typeof globalThis.fetch {
+  return (input, init) => {
+    const headers = new Headers(
+      init?.headers ??
+        (typeof input === 'object' && 'headers' in input
+          ? input.headers
+          : undefined),
+    )
+    const existing = headers.get('user-agent')
+    headers.set(
+      'user-agent',
+      existing ? `${existing} ${USER_AGENT_TOKEN}` : USER_AGENT_TOKEN,
+    )
+    return inner(input, { ...init, headers })
+  }
+}
diff --git a/packages/ai-sandbox-vercel/tests/user-agent.test.ts b/packages/ai-sandbox-vercel/tests/user-agent.test.ts
new file mode 100644
index 000000000..e75c21c0e
--- /dev/null
+++ b/packages/ai-sandbox-vercel/tests/user-agent.test.ts
@@ -0,0 +1,73 @@
+import { describe, expect, it, vi } from 'vitest'
+import { USER_AGENT_TOKEN, withSandboxUserAgent } from '../src/user-agent'
+
+function userAgentOf(init: RequestInit | undefined): string | null {
+  return new Headers(init?.headers).get('user-agent')
+}
+
+describe('withSandboxUserAgent', () => {
+  it('appends the token to an existing user-agent (as the SDK sends)', async () => {
+    const inner = vi
+      .fn<typeof globalThis.fetch>()
+      .mockResolvedValue(new Response())
+    const wrapped = withSandboxUserAgent(inner)
+
+    await wrapped('https://api.vercel.com/v2/sandboxes', {
+      headers: { 'user-agent': 'vercel/sandbox/2.2.1' },
+    })
+
+    const [, init] = inner.mock.calls[0]!
+    expect(userAgentOf(init)).toBe(`vercel/sandbox/2.2.1 ${USER_AGENT_TOKEN}`)
+  })
+
+  it('sets the token as the user-agent when none is present', async () => {
+    const inner = vi
+      .fn<typeof globalThis.fetch>()
+      .mockResolvedValue(new Response())
+    const wrapped = withSandboxUserAgent(inner)
+
+    await wrapped('https://api.vercel.com/v2/sandboxes')
+
+    const [, init] = inner.mock.calls[0]!
+    expect(userAgentOf(init)).toBe(USER_AGENT_TOKEN)
+  })
+
+  it('preserves other request init fields (method, body, signal)', async () => {
+    const inner = vi
+      .fn<typeof globalThis.fetch>()
+      .mockResolvedValue(new Response())
+    const wrapped = withSandboxUserAgent(inner)
+    const signal = new AbortController().signal
+
+    await wrapped('https://api.vercel.com/v2/sandboxes', {
+      method: 'POST',
+      body: '{"ok":true}',
+      signal,
+    })
+
+    const [, init] = inner.mock.calls[0]!
+    expect(init?.method).toBe('POST')
+    expect(init?.body).toBe('{"ok":true}')
+    expect(init?.signal).toBe(signal)
+  })
+
+  it('reads the user-agent off a Request input when no init is given', async () => {
+    const inner = vi
+      .fn<typeof globalThis.fetch>()
+      .mockResolvedValue(new Response())
+    const wrapped = withSandboxUserAgent(inner)
+
+    await wrapped(
+      new Request('https://api.vercel.com/v2/sandboxes', {
+        headers: { 'user-agent': 'vercel/sandbox/2.2.1' },
+      }),
+    )
+
+    const [, init] = inner.mock.calls[0]!
+    expect(userAgentOf(init)).toBe(`vercel/sandbox/2.2.1 ${USER_AGENT_TOKEN}`)
+  })
+
+  it('defaults to globalThis.fetch when no inner fetch is supplied', () => {
+    expect(typeof withSandboxUserAgent()).toBe('function')
+  })
+})