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# What `SubagentStart` runs once when Codex creates a thread-spawned subagent, before that child sends its first model request. Thread-spawned subagents use `SubagentStart` instead of the normal root-agent `SessionStart` hook. Configured handlers match on the subagent `agent_type`, using the same value passed to `spawn_agent`. When no agent type is specified, Codex uses the default agent type. Hook input includes the normal session-start fields plus: - `agent_id`: the child thread id. - `agent_type`: the resolved subagent type. `SubagentStart` may return `hookSpecificOutput.additionalContext`. That context is added to the child conversation before the first model request. # Lifecycle Scope Only thread-spawned subagents run `SubagentStart`. Internal/system subagents such as Review, Compact, MemoryConsolidation, and Other do not run normal `SessionStart` hooks and do not run `SubagentStart`. This avoids exposing synthetic matcher labels for internal implementation paths. Also the `SessionStart` hook no longer fires for subagents, this matches behavior with other coding agents' implementation # Stack 1. This PR: add `SubagentStart`. 2. #22873: add `SubagentStop`. 3. #22882: add subagent identity to normal hook inputs.
npm i -g @openai/codex
or brew install --cask codex
Codex CLI is a coding agent from OpenAI that runs locally on your computer.
If you want Codex in your code editor (VS Code, Cursor, Windsurf), install in your IDE.
If you want the desktop app experience, run
codex app or visit the Codex App page.
If you are looking for the cloud-based agent from OpenAI, Codex Web, go to chatgpt.com/codex.
Quickstart
Installing and running Codex CLI
Install globally with your preferred package manager:
# Install using npm
npm install -g @openai/codex
# Install using Homebrew
brew install --cask codex
Then simply run codex to get started.
You can also go to the latest GitHub Release and download the appropriate binary for your platform.
Each GitHub Release contains many executables, but in practice, you likely want one of these:
- macOS
- Apple Silicon/arm64:
codex-aarch64-apple-darwin.tar.gz - x86_64 (older Mac hardware):
codex-x86_64-apple-darwin.tar.gz
- Apple Silicon/arm64:
- Linux
- x86_64:
codex-x86_64-unknown-linux-musl.tar.gz - arm64:
codex-aarch64-unknown-linux-musl.tar.gz
- x86_64:
Each archive contains a single entry with the platform baked into the name (e.g., codex-x86_64-unknown-linux-musl), so you likely want to rename it to codex after extracting it.
Using Codex with your ChatGPT plan
Run codex and select Sign in with ChatGPT. We recommend signing into your ChatGPT account to use Codex as part of your Plus, Pro, Business, Edu, or Enterprise plan. Learn more about what's included in your ChatGPT plan.
You can also use Codex with an API key, but this requires additional setup.
Docs
This repository is licensed under the Apache-2.0 License.