EDIT: To everyone here, the solution was actually reasonably simple, just follow these instructions.
What version of the Codex App are you using (From “About Codex” dialog)?
26.611.61753
What subscription do you have?
Pro x20
What platform is your computer?
Darwin 25.3.0 arm64 arm
What issue are you seeing?
Repeatedly encountering in my GPT 5.4 xhigh session:
unexpected status 404 Not Found: Unknown error, url: https://chatgpt.com/backend-api/codex/responses, cf-ray: ...
I can send a message and get an update back, but then when the agent would think and continue I encountered this error 3 times in a row.
I have another session running with GPT 5.5 xhigh and it seems to be unaffected.
What steps can reproduce the bug?
I have a long running session going, it's had many compactions and plenty of steering. I've also been spinning up sub-agents for smaller tasks where this session is acting as an orchestrator. It failed shortly after steering it to spin up a sub-agent, not sure if that's related.
Session stopped with this error, it retried 5/5 times and gave up. This did not occur immediately after compaction, but it was shortly there after, maybe around 50k tokens.
Sending Continue did work, but it failed again after taking a turn. I tried this twice more and it does seem that for now the session is continuing on.
What is the expected behavior?
Don't die mid session.
Ideally we'd also have more error resistant retries with exponential back-off to something like 20 retries over 10 minutes.
Additional information
No response