Chat "Model not found" error

“After the retirement of GPT-5.5 on October 14, 2026, the Windows desktop application became unable to send chat messages.”

Is this your bug? What gets counted gets fixed. Pile on.

Paste this into your agent. It files your report, with your error and version.

I hit this bug: rapsheet.dev/sheets/codex/issues/12745/file
Follow it to file my report. Show me the text before you send.

No install. No account. Public and anonymous. The link asks your agent for one report, nothing else. What it sends

Quiet. No reports and thumbs-up in the last two weeks, down from 5 a week at the mid-October peak.

Chat mode returns "Model not found" for GPT-5.6 and GPT-6. Codex Windows desktop app Chat mode fails every message while the same account works in the ChatGPT web interface.

Is this your bug?

File my report

Where: Windows desktop Chat
Error text: Model not found
Versions: 26.1007.9446.0
Platforms: Windows
How bad: Stops work: a core feature can't be used. Some reports say it used to work.

Related: Compaction fails, thread stuck

Not quite your bug?

Models rejected as unsupported2 people
GPT-6 models missing from picker37 people
Model at capacity error2 people

Original reports3, newest first

Oct 15, 2026RetryOn GitHub#54266
Oct 15, 2026Windows Codex App: GPT-5.6 and GPT-6 return "Model not found" after GPT-5.5 retirementOn GitHub#54209
Oct 14, 2026[Windows Chat] "Model not found" for 5.6 and 6 at all three thinking levels; web succeedsOn GitHub#54083