The 'gpt-5.3-codex' model is not supported when using Codex with a ChatGPT account.
The message
The 'gpt-5.3-codex' model is not supported when using Codex with a ChatGPT account.What it means
OpenAI has retired that model for Codex when you're signed in with a ChatGPT account. Your request still names it, often from a saved setting, so the server refuses it.
What to do
Switch to a model your plan still offers: /model in the CLI, the picker in the app, or the model line in config.toml. OpenAI recommends gpt-6.1-sol where available. Then remove the old name from scripts, agents and scheduled tasks.
You'll get this from Codex when it asks for a model that your ChatGPT sign-in can't use any more. The model's name sits in the quotes, so the line changes with whatever model was requested. In some clients it arrives wrapped in JSON, inside a detail field.
The two GitHub issues we found were both opened on June 3, 2026 by Plus subscribers, one in the Codex app and one in Xcode, and both say Codex had worked the day before. OpenAI closed both as not planned.
Why it happens
OpenAI retired the model for ChatGPT accounts. Its Codex models page lists it under deprecated Codex models.
The gpt-5.2 and gpt-5.3-codex models are already deprecated in Codex when you sign in with ChatGPT.
So the request still names the old model, and the server turns it away. Often that's because the name is saved somewhere (config.toml, a script, a custom agent) and you forgot it was there.
How to fix it
Change the model. In the CLI, run /model, or start Codex with --model and a current name. In the app, use the picker under the composer. Then hunt down every place the old name is written: the model line in config.toml, codex exec --model commands, custom agents and scheduled tasks. The docs ask you to update all of them.
OpenAI recommends GPT-6.1 Sol, written gpt-6.1-sol, for complex coding where your account and client have it, and gpt-6-luna for focused, repeatable tasks. Availability depends on the rollout, your sign-in method and your client, so a model on the page may not be in your picker yet.
Codex can also sign in with your own API key instead of ChatGPT. The docs say that route isn't affected by the GPT-5.4 retirement, and they send you to the API models page for what the API still carries. Check there for the model you want before you switch.
GPT-5.5 is next
The docs say GPT-5.5 retires from ChatGPT, ChatGPT Work and Codex on every plan on October 14, 2026, while staying on the API. On Plus and up, OpenAI's suggested replacement is gpt-6-sol. On Free and Go, it's gpt-6-luna. The gpt-5.4 and gpt-5.4-mini models already went the same way on August 31, 2026.