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GPT-5.1-Codex-Max
GPT-5.1-Codex-Max is OpenAI’s latest agentic coding model, designed for long-running, high-context software development tasks. It is based on an updated version of the 5.1 reasoning stack and trained on agentic workflows spanning software engineering, mathematics, and research. GPT-5.1-Codex-Max delivers faster performance, improved reasoning, and higher token efficiency across the development lifecycle.
12/4/2025
400,000 tokens
Specifications
Modalities
Input
text
image
Output
text
Supported Parameters
include_reasoning
max_tokens
reasoning
response_format
seed
structured_outputs
tool_choice
tools
Max Output Tokens
128,000Reasoning Configuration
- Default
- Thinking on (effort: medium)
- Selectable effort levels
- xhighhighmediumlow
- Turning thinking off
- Not possible (always thinks)
Data policy
- Prompt retention
- Unknown — we could not confirm
- Training
- Unknown — not declared
"Unknown" does not mean "safe". It means we could not confirm it.
Whether a provider trains on prompts is a declared value from our terms with them. Retention is determined from the upstream listing for every host this model can reach. Neither is guessed.
Frequently asked questions
- Is GPT-5.1-Codex-Max available on FastMetal?
- Not at the moment. GPT-6.1 Sol, from the same lab, is available on the FastMetal API today.
- What is the context window of GPT-5.1-Codex-Max?
- 400,000 tokens, shared between the prompt and the response.