GPT-5.5 selected in Codex App but backend returns 404 Model not found

Resolved 💬 5 comments Opened Jun 8, 2026 by gf5ckszr2d-cell Closed Jun 12, 2026

💡 Likely answer: A maintainer (github-actions[bot], contributor) responded on this thread — see the highlighted reply below.

What version of the Codex App are you using (From “About Codex” dialog)?

v0.137.0

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Windows 11 x64

What issue are you seeing?

Codex App starts correctly and authenticates successfully.

Current configuration:

model = "gpt-5.5"
model_reasoning_effort = "medium"

The model appears in /status and can be selected successfully.

However, when sending any prompt, Codex returns:

unexpected status 404 Not Found: Model not found gpt-5.5

Additional output:

Falling back from WebSockets to HTTPS transport.
unexpected status 404 Not Found: Model not found gpt-5.5-codex-1p-exp-p-0604-811f2f-ev3-text-1-treatment

Request ID:
cdc4d6c6-d1e2-48fb-b350-3b2245db32fe

CF-Ray:
a083c4afceb93c1b-LIM

GPT-5.4 works correctly on the same installation and account.

Account type:
ChatGPT Plus

Codex version:
v0.137.0

Operating system:
Windows 11 x64

What steps can reproduce the bug?

Feedback ID: 019ea4a5-6373-7932-b443-e29f94a3cc11

Steps to reproduce:

Launch OpenAI Codex App v0.137.0.
Sign in with a ChatGPT Plus account.
Select model "gpt-5.5" (medium reasoning effort).
Start a new session.
Send a simple prompt such as:

hola

Result:

Codex fails and returns:

unexpected status 404 Not Found: Model not found gpt-5.5

Additional output:

Falling back from WebSockets to HTTPS transport.
unexpected status 404 Not Found: Model not found gpt-5.5-codex-1p-exp-p-0604-811f2f-ev3-text-1-treatment

GPT-5.4 works correctly on the same installation and account.

What is the expected behavior?

When GPT-5.5 is selected, Codex should successfully process prompts and generate responses, just like GPT-5.4.

The model appears in /status and can be selected successfully, so prompts should execute without returning a 404 error.

Additional information

Codex version: v0.137.0

Subscription: ChatGPT Plus

Platform: Windows 11 x64

Request ID:
cdc4d6c6-d1e2-48fb-b350-3b2245db32fe

CF-Ray:
a083c4afceb93c1b-LIM

The issue occurs only with GPT-5.5.
GPT-5.4 works normally on the same machine and account.

A feedback report was already submitted through the Codex App.
Feedback ID:
019ea4a5-6373-7932-b443-e29f94a3cc11

View original on GitHub ↗

5 Comments

github-actions[bot] contributor · 2 months ago

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

#26892
#26916
#26902
#26910

Powered by Codex Action

gwagwa2003 · 2 months ago

I am seeing the same issue from Taiwan / TPE region.

Environment:

OS: Windows
Codex CLI: 0.137.0
Codex App: previously installed, now uninstalled
Model selected/configured: gpt-5.5
Endpoint: https://chatgpt.com/backend-api/codex/responses

Error:

Falling back from WebSockets to HTTPS transport.
unexpected status 404 Not Found: Model not found gpt-5.5-codex-1p-exp-p-0604-811f2f-ev3-text-control

unexpected status 404 Not Found: Model not found gpt-5.5,
url: https://chatgpt.com/backend-api/codex/responses
cf-ray: a088c562ea774a39-TPE
request id: 74565b1f-e6c5-49c4-b993-b0125139faa9

This has persisted for more than 12 hours. It looks like gpt-5.5 is exposed in the local model selection/config, but the backend still returns 404 Model not found.

I have also tried removing the Codex App and using only Codex CLI, but the issue still occurs.

ax-openai · 2 months ago

Hi everyone! Sorry, we are looking into this. Will report back here shortly.

ax-openai · 2 months ago

Thanks for your patience. The backend issue causing gpt-5.5 requests to return 404 Model not found is now resolved.

Please try again. If it still fails, share a fresh request ID and timestamp.

ax-openai · 2 months ago

Closing as resolved. If this recurs, please open a new issue with a fresh request ID and timestamp.