AI Code Review at Scale: How OpenAI’s Codex Reviewer Earns Developer Trust

A Practical Approach to Verifying AI-Generated Code at Scale: Lessons from OpenAI’s Codex Reviewer Core question this post answers: When AI can write code far faster than humans can review it, how do we build a verification system that engineers actually trust and use every day? On December 1, 2025, OpenAI published one of the most concrete alignment progress updates of the year: a detailed case study of the dedicated code-review agent shipped with GPT-5-Codex and GPT-5.1-Codex-Max. This isn’t a research prototype — it’s running on every internal pull request at OpenAI, used proactively by engineers via the /review CLI …