OpenAI Codex CLI

OpenAI's Codex CLI is the terminal-native coding agent built for developers who think in shell sessions, not GUI panels. Written in Rust for speed, open-sourced under Apache 2.0, and backed by 75,000+ GitHub stars, it has become the fastest-growing CLI coding tool in history.

The agent reads your codebase, generates a plan, writes code, runs tests, and iterates, all within a sandboxed environment that prevents accidental damage to your system. On Terminal-Bench 2.0, GPT-5.3-Codex scores 77.3%, placing it among the top autonomous terminal agents.

The three-tier autonomy model is the design decision that matters most. Suggest mode requires approval for every action. Auto-Edit applies file changes automatically but asks before running commands.

Full-Auto gives the agent complete freedom to edit and execute. Combined with sandbox modes (workspace-write for safe local work, danger-full-access for unrestricted operation), this gives you precise control over how much rope you hand the AI. Enterprise teams behind corporate firewalls get custom CA cert support and structured network policies as of v0.116.0.

The pricing model is uniquely accessible: the CLI itself is free and open source, and you pay only through your existing ChatGPT subscription or API key. Plus ($20/month) gets you 30-150 messages per 5 hours, while the new Pro tier ($100/month) delivers 5x the usage.

For a limited promotional period, Codex is even included with ChatGPT Free. The catch is ecosystem lock-in, Codex CLI only works with OpenAI models, so you cannot swap in Claude or Gemini the way you can with Roo Code or Aider.