diff --git a/.changeset/protect-server-action-401.md b/.changeset/protect-server-action-401.md
new file mode 100644
index 00000000000..b11c18078d8
--- /dev/null
+++ b/.changeset/protect-server-action-401.md
@@ -0,0 +1,5 @@
+---
+'@clerk/nextjs': major
+---
+
+Return 401 instead of 404 for unauthenticated server action requests in `auth.protect()`
diff --git a/packages/nextjs/src/server/__tests__/clerkMiddleware.test.ts b/packages/nextjs/src/server/__tests__/clerkMiddleware.test.ts
index 69419e2d504..9e82f19c75c 100644
--- a/packages/nextjs/src/server/__tests__/clerkMiddleware.test.ts
+++ b/packages/nextjs/src/server/__tests__/clerkMiddleware.test.ts
@@ -518,6 +518,31 @@ describe('clerkMiddleware(params)', () => {
       expect((await clerkClient()).authenticateRequest).toBeCalled();
     });
 
+    it('returns 401 when protect is called, the user is signed out, and the request is a server action', async () => {
+      const req = mockRequest({
+        url: '/protected',
+        headers: new Headers({
+          'next-url': '/protected',
+          'next-action': '1',
+        }),
+        appendDevBrowserCookie: true,
+      });
+
+      authenticateRequestMock.mockResolvedValueOnce({
+        publishableKey,
+        status: AuthStatus.SignedOut,
+        headers: new Headers(),
+        toAuth: () => ({ tokenType: TokenType.SessionToken, userId: null }),
+      });
+
+      const resp = await clerkMiddleware(async auth => {
+        await auth.protect();
+      })(req, {} as NextFetchEvent);
+
+      expect(resp?.status).toEqual(401);
+      expect((await clerkClient()).authenticateRequest).toBeCalled();
+    });
+
     it('throws an unauthorized error when protect is called and the machine auth token is invalid', async () => {
       const req = mockRequest({
         url: '/protected',
diff --git a/packages/nextjs/src/server/protect.ts b/packages/nextjs/src/server/protect.ts
index 3171c263aea..7a1ea7a05d3 100644
--- a/packages/nextjs/src/server/protect.ts
+++ b/packages/nextjs/src/server/protect.ts
@@ -126,6 +126,9 @@ export function createProtect(opts: {
         // TODO: Handle runtime values. What happens if runtime values are set in middleware and in ClerkProvider as well?
         return redirectToSignIn();
       }
+      if (isServerActionRequest(request)) {
+        return unauthorized();
+      }
       return notFound();
     };
 
diff --git a/packages/upgrade/src/versions/core-3/changes/nextjs-protect-server-action-401.md b/packages/upgrade/src/versions/core-3/changes/nextjs-protect-server-action-401.md
new file mode 100644
index 00000000000..32f3203a89b
--- /dev/null
+++ b/packages/upgrade/src/versions/core-3/changes/nextjs-protect-server-action-401.md
@@ -0,0 +1,32 @@
+---
+title: '`auth.protect()` returns 401 instead of 404 for unauthenticated server actions'
+packages: ['nextjs']
+matcher: 'auth\.protect\('
+matcherFlags: 'm'
+category: 'breaking'
+---
+
+`auth.protect()` in `clerkMiddleware()` now returns a `401 Unauthorized` response instead of a `404 Not Found` when an unauthenticated request is made from a server action.
+
+Previously, unauthenticated server action requests would receive a `404` response, which made it difficult for client-side code to distinguish between "not found" and "not authenticated." The new behavior returns `401`, which is the semantically correct HTTP status code for unauthenticated requests.
+
+### Who is affected
+
+If your application uses `auth.protect()` inside `clerkMiddleware()` and you have server actions that may be called by unauthenticated users, the HTTP status code returned will change from `404` to `401`.
+
+### What to do
+
+If you have client-side error handling that checks for `404` responses from server actions when the user is signed out, update it to handle `401` instead:
+
+```diff
+try {
+  await myServerAction();
+} catch (error) {
+-  if (error.status === 404) {
++  if (error.status === 401) {
+    // Handle unauthenticated user
+  }
+}
+```
+
+No changes are required if you are not explicitly checking the HTTP status code in your error handling.