From the Codex docs, checked on 2026-10-04:
- Codex CLI works against your local repository. It inspects files, makes edits and runs the tools already installed on your machine.
- Codex Cloud gives each task its own workspace on the repositories you choose. Network access and credentials are set in the environment settings.
- Codex reads AGENTS.md files before it does any work.
A rough rule: work you want to watch and steer as it happens suits the CLI. Tasks you can hand off and review afterwards suit cloud. Reply with what you're using it for.