Codex CLI
Codex CLI is OpenAI's open-source terminal agent · GPT-powered, repo-aware, installed with npm.
Text reviewed October 5, 2026
Codex CLI is OpenAI's open-source terminal agent · GPT-powered, repo-aware, installed with npm.
Basic
Codex CLI launched April 2025 (not to be confused with the 2021 Codex model). Install via `npm i -g @openai/codex`; run `codex` in a repo. The agent reads your files, proposes changes, and executes shell commands. Built on o-series reasoning models with a custom "computer-using-agent" harness.
Deep
Codex CLI is Apache-2.0 licensed · same repo as the Codex IDE (VSCode) and Codex Cloud (web SaaS). The harness exposes shell commands, file diffs, and HTTP calls. Token cost is high · a single task may burn $2-$5.
Expert
Codex CLI uses the Responses API (OpenAI's structured tool-use endpoint) with a custom tool set: shell_exec, file_edit, file_read, web_fetch. Reasoning tokens are charged separately from output tokens, making it visibly more expensive than Claude Code or Aider. The Codex suite · CLI, IDE, Cloud · shares state via a cloud workspace, so users can hand off tasks between environments. OpenAI open-sourced the harness to establish a standard for computer-using agents.
Depending on why you're here
- ·OpenAI's official terminal AI coding tool
- ·Similar shape to Claude Code but uses GPT models
- ·Installed from npm · free to install but pay for API tokens
- ·npm install · runs from the terminal
- ·High token cost · reasoning tokens billed separately
- ·Best when you want the latest o-series model in your IDE
- ·Strategic move: OpenAI shipping open-source tooling to shape the agent standard
- ·Sets template for reasoning-model agent UX
- ·Competes with Claude Code, Aider on terminal share
- ·Apache-2.0 harness from OpenAI · reference for o-series agent integration
- ·Uses Responses API + custom tool set
- ·Designed around reasoning-heavy models
Codex CLI is OpenAI's answer to Claude Code · same shape, rival model. The terminal agent war is a proxy for frontier model loyalty.