diff --git a/packages/sdk/src/proxy/client.ts b/packages/sdk/src/proxy/client.ts
index 70ab0ff..b66d98d 100644
--- a/packages/sdk/src/proxy/client.ts
+++ b/packages/sdk/src/proxy/client.ts
@@ -23,6 +23,20 @@ export interface ProxyContext {
   remoteTools: Tool[];
 }
 
+/**
+ * Build the appropriate auth headers based on config.
+ */
+function buildAuthHeaders(config: StitchProxyConfig): Record<string, string> {
+    if (config.accessToken) {
+        const headers: Record<string, string> = { Authorization: `Bearer ${config.accessToken}` };
+        if (config.quotaProjectId) {
+            headers['X-Goog-User-Project'] = config.quotaProjectId;
+        }
+        return headers;
+    }
+    return { 'X-Goog-Api-Key': config.apiKey! };
+}
+
 /**
  * Forward a JSON-RPC request to Stitch.
  */
@@ -45,7 +59,7 @@ export async function forwardToStitch(
       headers: {
         'Content-Type': 'application/json',
         Accept: 'application/json',
-        'X-Goog-Api-Key': config.apiKey!,
+        ...buildAuthHeaders(config),
       },
       body: JSON.stringify(request),
     });
@@ -92,7 +106,7 @@ export async function initializeStitchConnection(
     headers: {
       'Content-Type': 'application/json',
       Accept: 'application/json',
-      'X-Goog-Api-Key': ctx.config.apiKey!,
+      ...buildAuthHeaders(ctx.config),
     },
     body: JSON.stringify({
       jsonrpc: '2.0',
diff --git a/packages/sdk/src/proxy/core.ts b/packages/sdk/src/proxy/core.ts
index 72633be..ba45892 100644
--- a/packages/sdk/src/proxy/core.ts
+++ b/packages/sdk/src/proxy/core.ts
@@ -32,6 +32,8 @@ export class StitchProxy implements StitchProxySpec {
   constructor(inputConfig?: Partial<StitchProxyConfig>) {
     const rawConfig = {
       apiKey: inputConfig?.apiKey || process.env.STITCH_API_KEY,
+      accessToken: inputConfig?.accessToken || process.env.STITCH_ACCESS_TOKEN,
+      quotaProjectId: inputConfig?.quotaProjectId || process.env.STITCH_PROJECT_ID || process.env.GOOGLE_CLOUD_PROJECT,
       url: inputConfig?.url || process.env.STITCH_MCP_URL,
       name: inputConfig?.name,
       version: inputConfig?.version,
@@ -40,8 +42,8 @@ export class StitchProxy implements StitchProxySpec {
     // Validate config
     this.config = StitchProxyConfigSchema.parse(rawConfig);
 
-    if (!this.config.apiKey) {
-      throw new Error('StitchProxy requires an API key (STITCH_API_KEY)');
+    if (!this.config.apiKey && !this.config.accessToken) {
+      throw new Error('StitchProxy requires an API key (STITCH_API_KEY) or access token (STITCH_ACCESS_TOKEN)');
     }
 
     this.server = new McpServer(
diff --git a/packages/sdk/src/spec/proxy.ts b/packages/sdk/src/spec/proxy.ts
index 7c1dbe3..ed88dfb 100644
--- a/packages/sdk/src/spec/proxy.ts
+++ b/packages/sdk/src/spec/proxy.ts
@@ -23,6 +23,12 @@ export const StitchProxyConfigSchema = z.object({
   /** API key for Stitch authentication. Falls back to STITCH_API_KEY. */
   apiKey: z.string().optional(),
 
+  /** Access token for Stitch authentication (Bearer). Falls back to STITCH_ACCESS_TOKEN. */
+  accessToken: z.string().optional(),
+
+  /** Quota project ID for billing. Required with accessToken auth. Falls back to STITCH_PROJECT_ID or GOOGLE_CLOUD_PROJECT. */
+  quotaProjectId: z.string().optional(),
+
   /** Target Stitch MCP URL. Default: https://stitch.googleapis.com/mcp */
   url: z.string().default(DEFAULT_STITCH_API_URL),
 
diff --git a/packages/sdk/test/proxy.test.ts b/packages/sdk/test/proxy.test.ts
index 7114ec3..2e7a623 100644
--- a/packages/sdk/test/proxy.test.ts
+++ b/packages/sdk/test/proxy.test.ts
@@ -43,9 +43,25 @@ describe('StitchProxy', () => {
     expect(proxy).toBeDefined();
   });
 
-  it('should throw if no API key is provided', () => {
+  it('should throw if neither API key nor access token is provided', () => {
     delete process.env.STITCH_API_KEY;
-    expect(() => new StitchProxy({})).toThrow("StitchProxy requires an API key");
+    delete process.env.STITCH_ACCESS_TOKEN;
+    expect(() => new StitchProxy({})).toThrow("StitchProxy requires an API key (STITCH_API_KEY) or access token (STITCH_ACCESS_TOKEN)");
+  });
+
+  it('should initialize with accessToken instead of apiKey', () => {
+    delete process.env.STITCH_API_KEY;
+    delete process.env.STITCH_ACCESS_TOKEN;
+    const proxy = new StitchProxy({ accessToken: 'test-token' });
+    expect(proxy).toBeDefined();
+  });
+
+  it('should initialize with STITCH_ACCESS_TOKEN env var', () => {
+    delete process.env.STITCH_API_KEY;
+    process.env.STITCH_ACCESS_TOKEN = 'env-token';
+    const proxy = new StitchProxy({});
+    expect(proxy).toBeDefined();
+    delete process.env.STITCH_ACCESS_TOKEN;
   });
 
   it('should connect to stitch and fetch tools on start', async () => {
@@ -99,6 +115,37 @@ describe('Proxy Client Error Handling', () => {
     vi.clearAllMocks();
   });
 
+  it('forwardToStitch should send Authorization: Bearer header when accessToken is configured', async () => {
+    mockFetch.mockResolvedValue({
+      ok: true,
+      json: async () => ({ result: 'ok' })
+    } as Response);
+
+    await forwardToStitch({ url: 'http://test', accessToken: 'my-token', quotaProjectId: 'my-project' } as any, 'testMethod');
+
+    const fetchCall = mockFetch.mock.calls[0];
+    expect(fetchCall[1].headers).toEqual(expect.objectContaining({
+      Authorization: 'Bearer my-token',
+      'X-Goog-User-Project': 'my-project',
+    }));
+    expect(fetchCall[1].headers).not.toHaveProperty('X-Goog-Api-Key');
+  });
+
+  it('forwardToStitch should send X-Goog-Api-Key header when only apiKey is configured', async () => {
+    mockFetch.mockResolvedValue({
+      ok: true,
+      json: async () => ({ result: 'ok' })
+    } as Response);
+
+    await forwardToStitch({ url: 'http://test', apiKey: 'my-api-key' } as any, 'testMethod');
+
+    const fetchCall = mockFetch.mock.calls[0];
+    expect(fetchCall[1].headers).toEqual(expect.objectContaining({
+      'X-Goog-Api-Key': 'my-api-key',
+    }));
+    expect(fetchCall[1].headers).not.toHaveProperty('Authorization');
+  });
+
   it('forwardToStitch should throw Stitch API error on non-ok response', async () => {
     mockFetch.mockResolvedValue({
       ok: false,