OpenAI Codex CLI Review (2026)

Codex CLI is OpenAI's open-source terminal coding agent, the spiritual response to Anthropic's Claude Code. It runs locally, executes in a sandboxed environment, and routes to GPT-5.1 (or o4 reasoning models) for planning and edits. The 2026 release added stable MCP support, multi-step plans, and a 'review mode' that asks for approval before any non-read action. It's noticeably faster than Claude Code on simple tasks and noticeably weaker on long-horizon reasoning. For engineers heavily invested in OpenAI infra, or who want a fully open-source agent they can audit and extend, it's the right pick.