OpenAI has released GPT-5.1-Codex-Max, built on GPT-5.1, optimized for long-horizon software engineering tasks with improved token efficiency and multi-hour agentic capabilities.
What’s new:
The model supports significantly longer tasks by handling context spanning millions of tokens through “compaction,” enabling workflows like extensive refactoring, prolonged debugging, and iterative coding sessions. In the Codex agent harness in the CLI, IDE extension, or cloud, it can work across multiple context windows, automatically pruning the session history to only retain context most relevant to the task at hand.
Benefits for developers:
- ~30% fewer reasoning tokens used compared to GPT-5.1-Codex (SWE-Bench Verified benchmark).
- Enhanced support for multi-file projects and extended coding loops.
- Verified compatibility with Windows environments and CLI workflows.
Availability:
GPT-5.1-Codex-Max is available immediately within Codex for ChatGPT Plus, Pro, Business, Edu, and Enterprise plans. API access is coming soon. It now replaces GPT-5.1-Codex as the default.
Check out the official announcement for more details.
We’d love to hear your feedback, benchmarks, or insights from your workflows!