bug(cli): gpt-5.5 returns 404 Model not found while gpt-5.4 works

What version of Codex are you using?

codex-cli 0.137.0

Which model were you using?

gpt-5.5

What operating system are you on?

Linux x86_64

What issue are you seeing?

Using Codex CLI with a ChatGPT account, gpt-5.5 is currently unusable while gpt-5.4 works on the same machine/account.

Observed behavior:

• Starting Codex with codex and defaulting or switching to gpt-5.5 fails.
• gpt-5.4 works from the same environment.
• Codex had been updated to the latest version roughly 30 minutes before reproduction.

Representative errors:

⚠ 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

unexpected status 404 Not Found: Model not found gpt-5.5, url: https://chatgpt.com/backend-api/codex/responses, cf-ray: a0884ce7586bca16-EZE, request id: db9ace7c-1ace-4d1a-8d2b-d6f7e82aaf6c

Model changed to gpt-5.5 low

unexpected status 404 Not Found: Model not found gpt-5.5, url: https://chatgpt.com/backend-api/codex/responses, cf-ray: a088508a598614a0-EZE, request id: ba2370ef-e800-43c1-aeaf-b34b2204bd49

This does not look like a generic local-network failure because another model (gpt-5.4) works in the same session/account.

Steps to reproduce

1. Update Codex CLI to the latest available version.
2. Run codex or codex --model gpt-5.5.
3. Sign in with a ChatGPT account if needed.
4. Send any prompt, or switch models to gpt-5.5 from within Codex.

Expected behavior

gpt-5.5 should accept requests when selectable/available, or Codex should return a clearer entitlement/availability message instead of a backend 404 Model not found.

Actual behavior

Requests to gpt-5.5 fail with backend 404 Not Found: Model not found gpt-5.5, while gpt-5.4 remains usable.

Additional context

• This resembles the earlier April 2026 Codex incidents involving intermittent not found errors for gpt-5.5.
• Public status currently shows Codex operational, so this may be a partial rollout / entitlement / catalog mismatch rather than a fully declared outage.