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.

ChatOpenAI400k tokens$1.3626 / $10.9006 · 1M

openai/gpt-5.1-codex-max

Context
400k tokens
Completion cap
128,000
Tools
Yes
JSON
Yes
Released
2025-12-04

Call it from Geek Hub

Same OpenAI SDK. Change the base URL and the model id.

curl https://api.geekhub.mx/v1/chat/completions \
  -H "Authorization: Bearer $GEEKHUB_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.1-codex-max",
    "messages": [{"role": "user", "content": "Hola"}]
  }'
Get an API key

Frequently asked questions

What is 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. GPT-5.1-Codex-Max runs on the Geek Hub API (OpenAI-compatible). Model id: openai/gpt-5.1-codex-max.
Is GPT-5.1-Codex-Max free?
No. Input is $1.3626 per 1M tokens and output is $10.9006 per 1M tokens on Geek Hub (markup included).
What is the context length of GPT-5.1-Codex-Max?
GPT-5.1-Codex-Max has a 400k tokens context window. It supports up to 128,000 completion tokens.
Does GPT-5.1-Codex-Max support tool calling and structured outputs?
GPT-5.1-Codex-Max accepts tools and tool_choice for function calling. It also supports structured outputs via a JSON schema in response_format.
When was GPT-5.1-Codex-Max released?
GPT-5.1-Codex-Max was released on 2025-12-04.

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