Running Claude Code and Codex side by side

Claude Code and Codex are good at different things, and it is common to want one reviewing what the other wrote. Here is how to run both in the same project, at the same time, without juggling two terminals.

Install both

Open Settings › Features (⌘,) and turn on sessions. Then, in Settings › Agents, install Claude Agent (claude-acp) and Codex (codex-acp) from the ACP registry. Both ship as npm packages, so Node.js has to be on your PATH. Each agent signs in the way it does on its own.

One session each

Open your project with ⌘O. ⌘N starts a session on the agent the project last used; ⌥⌘N starts one on the next agent you have installed. Press ⌘N for Claude Code, then ⌥⌘N for Codex. The two sessions run independently: a turn in one never waits for the other.

Watch both

Drag the Codex session's tab onto the edge of the pane to divide it in two, and ⌃⇥ steps between the panes. Each pane keeps its own scroll and selection, so following Codex never loses your place in Claude Code's transcript.

Hand out work from a board

Make a board for the task and write a card for each piece. ▶ on a card sends it to a session you pick; ▶ on a column's heading sends every card in it that is neither busy nor blocked. A card spins while an agent has it, and clicking it follows the work into the transcript.

Keep what they find

Both agents get Cydonia's MCP tools, so a turn can end as an article in the project instead of scrollback. Ask one to write up its plan as an article, then ask the other to review it. Both read the same file in .cydonia/, and the link #12 means the same entry to either.

See Running several agents for the rest.