OpenAI spills technical details about how its AI coding agent works

On Friday, OpenAI engineer Michael Bolin published a detailed technical breakdown of how the company’s Codex CLI coding agent works internally, offering developers insight into AI coding tools that can write code, run tests, and fix bugs with human supervision. It complements our article in December on how AI agents work by filling in technical details on how OpenAI implements its “agentic loop.”

AI coding agents are having something of a “ChatGPT moment,” where Claude Code with Opus 4.5 and Codex with GPT-5.2 have reached a new level of usefulness for rapidly coding up prototypes, interfaces, and churning out boilerplate code. The timing of OpenAI’s post details the design philosophy behind Codex just as AI agents are becoming more practical tools for everyday work.

These tools aren’t perfect and remain controversial for some software developers. While OpenAI has previously told Ars Technica that it uses ...