diff --git a/.changeset/dull-forks-agree.md b/.changeset/dull-forks-agree.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/dull-forks-agree.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/integration/templates/tanstack-react-start/package.json b/integration/templates/tanstack-react-start/package.json
index 7e86c3cb0ab..bf45f3efb8d 100644
--- a/integration/templates/tanstack-react-start/package.json
+++ b/integration/templates/tanstack-react-start/package.json
@@ -13,7 +13,6 @@
     "@tanstack/react-start": "1.132.51",
     "react": "18.3.1",
     "react-dom": "18.3.1",
-    "srvx": "0.8.15",
     "tailwind-merge": "^2.5.4"
   },
   "devDependencies": {
diff --git a/packages/backend/src/tokens/__tests__/clerkRequest.test.ts b/packages/backend/src/tokens/__tests__/clerkRequest.test.ts
index 18c5c72ece0..35a5625afe0 100644
--- a/packages/backend/src/tokens/__tests__/clerkRequest.test.ts
+++ b/packages/backend/src/tokens/__tests__/clerkRequest.test.ts
@@ -204,4 +204,39 @@ describe('createClerkRequest', () => {
       expect(json.cookies).toBe('{}');
     });
   });
+
+  describe('duck typing detection (instanceof workaround)', () => {
+    it('should create a new ClerkRequest from a regular Request', () => {
+      const regularRequest = new Request('http://localhost:3000');
+      const clerkRequest = createClerkRequest(regularRequest);
+
+      expect(clerkRequest).not.toBe(regularRequest);
+      expect(clerkRequest.clerkUrl).toBeDefined();
+      expect(clerkRequest.cookies).toBeDefined();
+    });
+
+    it('should return an existing ClerkRequest instance unchanged', () => {
+      const firstClerkRequest = createClerkRequest(new Request('http://localhost:3000'));
+      const secondClerkRequest = createClerkRequest(firstClerkRequest);
+
+      expect(secondClerkRequest).toBe(firstClerkRequest);
+    });
+
+    it('should work correctly with bundler-scoped Request classes', () => {
+      // Simulate bundler creating a scoped Request class (like Request$1)
+      class RequestScoped extends Request {
+        constructor(input: RequestInfo | URL, init?: RequestInit) {
+          super(input, init);
+        }
+      }
+
+      const scopedRequest = new RequestScoped('http://localhost:3000');
+      const clerkRequest = createClerkRequest(scopedRequest);
+
+      // Should create a new ClerkRequest even though scopedRequest is a different Request class
+      expect(clerkRequest).not.toBe(scopedRequest);
+      expect(clerkRequest.clerkUrl).toBeDefined();
+      expect(clerkRequest.cookies).toBeDefined();
+    });
+  });
 });
diff --git a/packages/backend/src/tokens/clerkRequest.ts b/packages/backend/src/tokens/clerkRequest.ts
index f35b079d779..89ab5e6bc6d 100644
--- a/packages/backend/src/tokens/clerkRequest.ts
+++ b/packages/backend/src/tokens/clerkRequest.ts
@@ -82,7 +82,12 @@ class ClerkRequest extends Request {
 }
 
 export const createClerkRequest = (...args: ConstructorParameters<typeof ClerkRequest>): ClerkRequest => {
-  return args[0] instanceof ClerkRequest ? args[0] : new ClerkRequest(...args);
+  // Use duck typing instead of instanceof to avoid issues with polyfilled Request classes
+  // (e.g., in TanStack Start or other environments with multiple Request class instances)
+  // ClerkRequest has unique properties 'clerkUrl' and 'cookies' that distinguish it from Request
+  const isClerkRequest = args[0] && typeof args[0] === 'object' && 'clerkUrl' in args[0] && 'cookies' in args[0];
+
+  return isClerkRequest ? (args[0] as ClerkRequest) : new ClerkRequest(...args);
 };
 
 export type { ClerkRequest };
diff --git a/packages/nextjs/src/__tests__/keyless-custom-headers.test.ts b/packages/nextjs/src/__tests__/keyless-custom-headers.test.ts
index 48cc8cb896e..7be75419d7a 100644
--- a/packages/nextjs/src/__tests__/keyless-custom-headers.test.ts
+++ b/packages/nextjs/src/__tests__/keyless-custom-headers.test.ts
@@ -166,7 +166,7 @@ describe('keyless-custom-headers', () => {
   });
 
   describe('formatMetadataHeaders', () => {
-    it('should format complete metadata object with all fields present', () => {
+    it('should format complete metadata object with all fields present', async () => {
       const metadata = {
         nodeVersion: 'v18.17.0',
         nextVersion: 'next-server (v15.4.5)',
@@ -181,7 +181,7 @@ describe('keyless-custom-headers', () => {
         isCI: false,
       };
 
-      const result = formatMetadataHeaders(metadata);
+      const result = await formatMetadataHeaders(metadata);
 
       // Test exact header casing and values
       expect(result.get('Clerk-Node-Version')).toBe('v18.17.0');
@@ -196,7 +196,7 @@ describe('keyless-custom-headers', () => {
       expect(result.get('Clerk-Auth-Status')).toBe('signed-out');
     });
 
-    it('should handle missing optional fields gracefully', () => {
+    it('should handle missing optional fields gracefully', async () => {
       const metadata = {
         userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)',
         host: 'localhost:3000',
@@ -208,7 +208,7 @@ describe('keyless-custom-headers', () => {
         // Missing: nodeVersion, nextVersion, npmConfigUserAgent, port
       };
 
-      const result = formatMetadataHeaders(metadata);
+      const result = await formatMetadataHeaders(metadata);
 
       // Test that only present fields are set
       expect(result.get('Clerk-Client-User-Agent')).toBe('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)');
@@ -225,7 +225,7 @@ describe('keyless-custom-headers', () => {
       expect(result.get('Clerk-Node-Port')).toBeNull();
     });
 
-    it('should handle undefined values for optional fields', () => {
+    it('should handle undefined values for optional fields', async () => {
       const metadata = {
         nodeVersion: undefined,
         nextVersion: undefined,
@@ -240,7 +240,7 @@ describe('keyless-custom-headers', () => {
         isCI: false,
       };
 
-      const result = formatMetadataHeaders(metadata);
+      const result = await formatMetadataHeaders(metadata);
 
       // Test that undefined fields are not set
       expect(result.get('Clerk-Node-Version')).toBeNull();
@@ -257,7 +257,7 @@ describe('keyless-custom-headers', () => {
       expect(result.get('Clerk-Auth-Status')).toBe('test-auth-status');
     });
 
-    it('should handle empty string values', () => {
+    it('should handle empty string values', async () => {
       const metadata = {
         nodeVersion: '',
         nextVersion: '',
@@ -272,7 +272,7 @@ describe('keyless-custom-headers', () => {
         isCI: false,
       };
 
-      const result = formatMetadataHeaders(metadata);
+      const result = await formatMetadataHeaders(metadata);
 
       // Empty strings should not be set as headers
       expect(result.get('Clerk-Node-Version')).toBeNull();
@@ -513,7 +513,7 @@ describe('keyless-custom-headers', () => {
 
     // Collect metadata and format headers
     const metadata = await collectKeylessMetadata();
-    const headers = formatMetadataHeaders(metadata);
+    const headers = await formatMetadataHeaders(metadata);
 
     // Verify the full pipeline works correctly
     expect(headers.get('Clerk-Client-User-Agent')).toBe('Integration-Test-Agent');
diff --git a/packages/nextjs/src/server/keyless-custom-headers.ts b/packages/nextjs/src/server/keyless-custom-headers.ts
index ff016d028e7..73ca03837b6 100644
--- a/packages/nextjs/src/server/keyless-custom-headers.ts
+++ b/packages/nextjs/src/server/keyless-custom-headers.ts
@@ -99,7 +99,7 @@ function getNextVersion(): string | undefined {
 /**
  * Converts metadata to HTTP headers
  */
-export function formatMetadataHeaders(metadata: MetadataHeaders): Headers {
+export async function formatMetadataHeaders(metadata: MetadataHeaders): Promise<Headers> {
   const headers = new Headers();
 
   if (metadata.nodeVersion) {