Back to timeline

GPT-5.1-Codex-Max

OpenAI introduces GPT-5.1-Codex-Max, a frontier agentic coding model built for long-running tasks via compaction.

Model Release

What Happened

OpenAI introduced GPT-5.1-Codex-Max as a new frontier model for agentic coding in Codex, highlighting long-running tasks and a compaction mechanism for sustaining work over very long sessions.

Why It Matters

This release illustrates the “agent reliability” direction: not just writing code, but persisting across hours-long workflows, iterating on tests, and maintaining coherence across repeated context windows.

Technical Details