# Codex environments

In the ChatGPT desktop app, open the ChatGPT dropdown and select **Codex**.
When starting a Codex chat, choose where it runs:

- **Local**: work directly in your current project directory.
- **Worktree**: isolate changes in a Git worktree. [Learn more](https://learn.chatgpt.com/docs/environments/git-worktrees).
- **Cloud**: run remotely in a configured cloud environment.

Both **Local** and **Worktree** chats run on your computer.

For the full glossary and concepts, explore the [concepts section](https://learn.chatgpt.com/docs/prompting).

<CodexScreenshot
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  darkSrc="/images/codex/app/modes-dark.webp"
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/>