OpenAI Codex Review

Codex started as a terminal tool in April 2025 and spent the following year turning into the whole surface. There is a CLI, a cloud agent that takes a task and returns a pull request, extensions for VS Code, JetBrains and Xcode, a web view inside ChatGPT, and since February 2026 a desktop application for Windows and macOS that merged into the ChatGPT desktop app in July. Five million weekly active developers by June settles the argument about whether anyone is actually using it.

The model line did the heavy lifting. Codex-1 was a variant of o3. GPT-5.3-Codex followed on February 5, 2026, with a Spark variant running on Cerebras hardware at roughly fifteen times the speed, and that changes what the tool is for: a model that answers in a second gets used inside the edit loop, not just for the long jobs. GPT-5.4 arrived on March 5. Codex Security, a vulnerability scanner built on the same agent, shipped in March, and the acquisition of the Python toolmaker Astral brought tooling that most of its users already depended on in house.

The reservation is the meter, as it is with everything OpenAI ships in this category. Codex draws agent credits from a ChatGPT plan rather than a flat allowance, and it shares that pool with Work, so two products compete for one budget and a heavy afternoon can end both. There is nothing extra to buy: it comes with Plus at $20 a month, Pro at $100 to $200, and with Business and Enterprise seats.