January 23, 2026

Unrolling the Codex agent loop

Codex CLI⁠(opens in a new window) is our cross-platform local software agent, designed to produce high-quality, reliable software changes while operating safely and efficiently on your machine. We’ve learned a tremendous amount about how to build a world-class software agent since we first launched the CLI in April⁠. To unpack those insights, this is the first post in an ongoing series where we’ll explore various aspects of how Codex works, as well as hard-earned lessons. (For an even more granular view on how the Codex CLI is built, check out our open source repository at https://github.com/openai/codex⁠(opens in a new window). Many of the finer details of our design decisions are memorialized in GitHub issues and pull requests if you’d like to learn more.)