GPT-5.1 Codex
RetiredOpenAI retired this model on 23 July 2026, so you can't start new chats with it. Use GPT-5.3 Codex instead. Your previous conversations are still available.
Built for programming and long, self-directed coding tasks. Not meant for general chat.
- Best for
- Coding, deep reasoning, and agent workflows
- Superseded by
- GPT-5.2 Codex
Context window
400,000 tokens
≈ 300,000 words · about 1,200 pages
Max output
128,000 tokens
≈ 96,000 words in a single answer
Knowledge cutoff
September 2024
its training cutoff
Modalities
- TextInput and output
- ImageInput only
- AudioNot supported
- VideoNot supported
Reasoning effort
Features
- StreamingSupported
- Function callingSupported
- Structured outputsSupported
- Fine-tuningNot supported
Ready to try it?
Polymeti is currently invite-only.
Log inBring your own API key · Your chats stay in your browser