Claude Code + Codex Plugin: Two AI Brains, One Terminal

You're debugging a gnarly race condition. Claude Code has been going at it for 10 minutes — reading files, forming theories, running tests. Then it hits a wall. Same hypothesis, same failed fix, third attempt. What if you could call in a second brain — a completely different model with fresh eyes — without leaving your terminal? That's what the Codex plugin for Claude Code does. It puts OpenAI's Codex (powered by GPT-5.4) inside your Claude Code session as a callable rescue agent. Two models. Two reasoning styles. One shared codebase. What Is It, Exactly? The Codex plugin is a Claude Code plugin — not a standalone tool. It lives inside your Claude Code session and gives you slash commands to dispatch tasks to OpenAI's Codex CLI. Think of it as a second engineer sitting next to you. Claude (Opus) is your primary — it has the full conversation context, knows your project, runs your tools. Codex is your specialist — you hand it a focused task, it works in a sandboxed environment, and retu