Building more with GPT-5.1-Codex-Max

Introduction

We’re introducing GPT‑5.1‑Codex‑Max, our new frontier agentic coding model, available in Codex today.  GPT‑5.1‑Codex‑Max is built on an update to our foundational reasoning model, which is trained on agentic tasks across software engineering, math, research, and more. GPT‑5.1‑Codex‑Max is faster, more intelligent, and more token-efficient at every stage of the development cycle–and a new step towards becoming a reliable coding partner.

GPT‑5.1‑Codex‑Max is built for long-running, detailed work. It’s our first model natively trained to operate across multiple context windows through a process called compaction, coherently working over millions of tokens in a single task. This unlocks project-scale refactors, deep debugging sessions, and multi-hour agent loops.

GPT‑5.1‑Codex‑Max is available in Codex today for use in the CLI, IDE extension, cloud, and code review, and API access is coming soon.

Frontier coding capabilities

GPT‑5.1‑Codex‑Max was trained on real-world software engineering tasks, like PR creation, code review, frontend coding, and Q&A and outperforms our previous models on many frontier coding evaluations. The model’s gains on benchmarks also come with improvements to real-world usage: GPT‑5.1‑Codex‑Max is the first model we have trained to operate in Windows environments, and the model’s training now includes tasks designed to make it a better collaborator in the Codex CLI.

Speed and cost

GPT‑5.1‑Codex‑Max shows significant improvements in token efficiency due to more effective reasoning. On SWE-bench Verified, GPT‑5.1‑Codex‑Max with ‘medium’ reasoning effort achieves better performance than GPT‑5.1‑Codex with the same reasoning effort, while using 30% fewer thinking tokens. For non-latency-sensitive tasks, we’re also introducing a new Extra High (‘xhigh’) reasoning effort, which thinks for an even longer period of time for a better answer. We still recommend medium as the daily driver for most tasks.