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Codex CLI

OpenAI's open-source terminal coding agent, rewritten in Rust.

Open official site developers.openai.com/codex/cliFree tier available · from $20/moAI Coding ToolsAI Agents

Codex CLI runs in the terminal, reads the repository, edits files and runs commands. The client is Apache-2.0 and installs locally; the intelligence comes from your ChatGPT plan or API credits. The Rust rewrite made startup and long-session behaviour noticeably steadier than the original TypeScript version.

The path here is almost always a ChatGPT subscription you already have. That makes the choice less about capability than about which vendor's meter you would rather be on, because the tool is not portable — leaving OpenAI means leaving Codex CLI. Worth knowing before you build habits around it: this is the first-party delivery mechanism for a model, so its prompts are tuned by the same people who trained it, and that tuning is a real advantage you give up by going model-agnostic.

Our take

The obvious choice if your team already pays for ChatGPT, because the agent comes with the plan rather than as another line item. The client being open source matters more than it sounds: you can read what it sends and pin a version. What you are buying is the model behind it, not the tool, and that is worth being clear about — switching away from OpenAI means switching tools too.

Last checked 2026-09-02

Best for

  • Teams already on a ChatGPT plan who want an agent without a new subscription
  • Command-line workflows where the editor is not the centre of gravity
  • People who want to read the client source before granting it shell access

Limitations

  • Tied to OpenAI models; the open-source client does not make it portable
  • Cost tracks steps executed, not questions asked
  • Long autonomous runs still need a human to check the result

When to pick something else

  • Anyone who needs to route work to a different model provider
  • Environments where a tool may not run shell commands
  • Fixed, repeatable steps that a plain script would do more cheaply

Key features

  • Open-source client, runs entirely on your machine
  • Reads the repository and edits across files
  • Runs commands and acts on the output
  • Works from a ChatGPT plan or API credits

Codex CLI alternatives

If Codex CLI is not the right fit, these solve similar problems.

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