What is OpenAI Codex?
Codex is OpenAI's coding agent: it works from the terminal, from an editor extension, from the web and from mobile, and it is included in whichever ChatGPT subscription you already have. It can work in the cloud on several tasks in parallel, review pull requests automatically and run code in a sandboxed environment. Its CLI is open source.
Pros
- Included in the ChatGPT subscription you already pay for
- Its CLI is open source and accepts your own API key
- Works in the cloud on several tasks at once
- There is some usage, though limited, even on the free plan
Cons
- Since April 2026 it bills against token credits: hard to predict
- Real heavy usage runs to $100-200 a month per developer
- Limits are shared across terminal, web and editor
Frequently asked questions
Is Codex free?
There is limited use on the free ChatGPT plan, and the CLI is free if you connect your own API key and pay for the tokens. For serious use, plans run from $8/month (Go) to $200/month (Pro).
How is it billed?
Since 2 April 2026, usage on Plus, Pro, Business and Enterprise is deducted from token credits rather than per message, which makes spending less predictable.
Codex or Claude Code?
Both are powerful terminal agents. Codex is good value if you already pay for ChatGPT; Claude Code is the benchmark for many developers on long tasks over large repositories.