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

128,000