---
id: "openai/gpt-5.1-codex-max"
also: ["openai/gpt-5.1-codex-max-20251204", "vercel/openai/gpt-5.1-codex-max"]
cheapest_list_usd_per_m: "1.25 in, 10.0 out, at azure on openrouter"
cheapest_effective_usd_per_m: "0.1953 in, 10.0 out, at azure on vercel"
context: 400000
max_output: 128000
input: ["text", "image"]
output: ["text"]
released: "2025-12-04"
reasoning: ["xhigh", "high", "medium", "low"]
api: ["/api/v1/chat/completions", "/api/v1/completions", "/api/v1/messages", "/api/v1/responses"]
params: ["include_reasoning", "max_completion_tokens", "max_tokens", "reasoning", "reasoning_effort", "response_format", "seed", "stop", "structured_outputs", "temperature", "tool_choice", "tools", "verbosity"]
endpoints: 2
gateways: "openrouter (1), vercel (1)"
no_training: 2
trains: 0
retains_prompts: 0
---
# OpenAI: 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...