Codex backend returns 404 across CLI, VS Code and Desktop; codex login fails with 500

What issue are you seeing?

Codex suddenly stopped working across all clients for the same ChatGPT account.

The issue reproduces in:

• Codex CLI
• VS Code Codex extension
• Codex Desktop

Changing the model does not help.

Regular ChatGPT continues to work normally with the same account.

CLI / VS Code error

Both CLI and VS Code return:

unexpected status 404 Not Found: Unknown error,
url: https://chatgpt.com/backend-api/codex/responses

Example Cloudflare ray:

cf-ray: a3559b4d190ef5f4-EWR

Before falling back to HTTPS, WebSocket also fails:

Falling back from WebSockets to HTTPS transport.
unexpected status 403 Forbidden,
url: wss://chatgpt.com/backend-api/codex/responses

Example Cloudflare ray for the WebSocket failure:

cf-ray: a3559b018b733608-FRA

Codex login also fails

I tried re-authenticating:

codex logout
codex login

The browser authentication flow opens correctly.

After selecting the same ChatGPT account, the browser shows:

Route Error

500 Internal Server Error

Because of this, the Codex login flow cannot complete.

What steps can reproduce the bug?

1. Start Codex CLI, VS Code extension, or Codex Desktop.
2. Submit any prompt.
3. The request fails.
4. Switching to another Codex model produces the same result.
5. Run codex login.
6. Select the ChatGPT account in the browser.
7. Authentication fails with 500 Internal Server Error.

What is the expected behavior?

Codex should successfully authenticate and requests to:

https://chatgpt.com/backend-api/codex/responses

should complete normally.

Additional information

Since the same failure occurs across three different Codex clients, multiple models, and also affects the Codex browser authentication flow, this appears to be related to the Codex backend / authentication / account entitlement flow rather than a client-specific configuration issue.

Start by reproducing the failure with the documented Codex CLI commands and the /backend-api/codex/responses endpoint across the named clients. The payload names no repository files or tests, so trace the backend and browser authentication entry points before determining whether the issue is actionable in this repository. Done means login completes and requests succeed normally.