[macOS][26.901.20858] Codex returns 404 on /backend-api/codex/responses while web works

What version of the Codex App are you using?

ChatGPT Desktop 26.901.20858 (macOS)
Bundled Codex CLI: 0.153.0-alpha.5

What subscription do you have?

ChatGPT Pro

What platform is your computer?

macOS, Apple Silicon

What issue are you seeing?

After updating ChatGPT Desktop to 26.901.20858, every Codex/Work prompt in the desktop app fails after reconnect attempts with:

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

The same ChatGPT account works normally in Codex/Work on chatgpt.com in the browser on the same Mac and network.

The bundled CLI reproduces the same failure:

Falling back from WebSockets to HTTPS transport.
unexpected status 404 Not Found: Unknown error,
url: wss://chatgpt.com/backend-api/codex/responses

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

Troubleshooting already attempted

• Fully quit and restarted ChatGPT Desktop.
• Signed out and signed back in.
• Reinstalled the current ChatGPT app by replacing the existing app bundle.
• Tested new and existing Codex conversations.
• Confirmed the browser version works on the same account/network.
• Confirmed bundled CLI auth is valid: Logged in using ChatGPT.
• Confirmed config parses successfully.

Codex doctor findings

codex doctor --json reports:

• auth.credentials: ok
• config.load: ok
• desktop.app_server.handshake: ok
• desktop.security.enforcement: ok
• installation: ok
• network.env: ok (no proxy configured, direct connection)
• network.provider_reachability: warning, ChatGPT inference URL returns HTTP 404
• network.websocket_reachability: warning, WebSocket handshake returns HTTP 404
• local state/sqlite integrity checks: ok

Effective model/config:

approval_policy = "on-request"
model = "gpt-5.6-sol"
model_reasoning_effort = "ultra"
sandbox_mode = "danger-full-access"

Steps to reproduce

1. Open ChatGPT Desktop 26.901.20858 on macOS.
2. Open Work/Codex.
3. Start any new conversation.
4. Send any prompt.
5. Observe reconnect attempts up to 5/5.
6. Request fails with 404 from /backend-api/codex/responses.
7. Open chatgpt.com on the same Mac/account/network.
8. Work/Codex works normally in the browser.
9. Running the bundled CLI directly also reproduces the same 404.

Expected behavior

Desktop Codex should send prompts normally, matching the working web client.

Additional information

This began immediately after the desktop update. Because web works while both Desktop and the bundled CLI fail, this appears to be a regression in the desktop/bundled Codex client or its backend routing rather than an account-wide or network-wide outage.

Related current reports appear to include Windows cases on the same desktop build and bundled core version.

Start with the bundled Codex CLI request path and the desktop app's handling of /backend-api/codex/responses, using the reported doctor diagnostics and WebSocket/HTTPS failures. Compare those requests with the working browser client; done means Desktop and the bundled CLI can send prompts without 404 responses.