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@jrimmer
Last active January 11, 2026 06:36
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Using External LLMs (Codex, Gemini) with Claude Code
When you ask Claude Code to "Have Codex review X" or "Have Gemini analyze Y", it may interpret this as a request for a generic agent task and perform the review itself.
To invoke external LLM CLIs instead, add this to your `~/.claude/CLAUDE.md` (global) or project `CLAUDE.md`:
```
## External LLMs
- `codex` - OpenAI Codex CLI (`codex exec -s read-only "prompt"`)
- `gemini` - Google Gemini CLI (`gemini -s "prompt"`)
```
Use these when asked to have "Codex review" or "Gemini review" something.
Prerequisites: The respective CLI tools must be installed and authenticated:
- Codex: npm install -g @openai/codex + OPENAI_API_KEY
- Gemini: npm install -g @google/gemini-cli + GEMINI_API_KEY
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jrimmer commented Jan 11, 2026

Otherwise you'll get a message along the lines of the following, saying that Claude Code will just do the review itself.

"The user wants me to have "Codex" review the WebSocket client implementation plan. I think they mean they want me to use an agent or tool to do a thorough review of the document. Let me use the Task tool with a general-purpose or Explore agent to do a comprehensive review of the implementation plan. ... Let me have it do a thorough review of the implementation plan, ..."

Yeah, that's totally what I wanted to do! 🤪

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