How to run Codex sessions in parallel

Running them side by side works the same way it does for Claude Code. One of them will always be stopped.

Table of contents

Why it stops

Codex asks before it runs a command.

Claude Code takes --permission-mode, which skips the asking. Grok has --permission-mode auto and muse has --yolo.

Codex is passed none of these. There is per-MCP-server auto-approval, but nothing that waives approval as a whole. Run several in parallel and somebody is always waiting on you.

Being told that it stopped

Codex 0.156 added hooks. PermissionRequest fires when the approval dialog is shown, and was measured firing then and on no other tool call.

Wiring it yourself is one flag at launch:

codex -c 'hooks.PermissionRequest=[{hooks=[{type="command",command="curl -s -X POST http://127.0.0.1:8080/waiting || true"}]}]'

Three things to get right:

  1. Codex asks you to trust the hook once. A “Hooks need review” dialog appears, and nothing fires until you accept. It asks again whenever the command’s text changes, so keep anything per-session in an environment variable and the command itself constant
  2. End with || true. Codex reads the hook’s exit status, so a server that is down must not read as a refusal
  3. Read “finished” from somewhere else. Turn boundaries are appended to the rollout file, and reading that needs no trust prompt

With MulmoTerminal

Both halves are wired already.

npx mulmoterminal@latest

Pick Codex in a cell and the cell changes colour when it is waiting, with a different sound from the one for finished.

The hook is not registered on Windows — the command leans on shell expansion that has not been measured there. It is also skipped when a seed prompt is passed, because the prompt would be typed into the trust dialog and lost.

日本語版: codex-parallel

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