Set up an agent
Turn on Claude Code, Codex CLI, or OpenCode, then sign in with your subscription or an API key.
Turning an agent on installs it for you. There is nothing to download by hand and no terminal setup. Within a minute you can start a chat on Claude Code, Codex CLI, or OpenCode from the composer.
Turn the agent on
- Open Extensions → Harnesses.
- Find Claude Code, Codex CLI, or OpenCode and flip its switch. The card reads Turn on to install the first time; Mach Studio downloads and installs the agent on this computer, then switches it on.
- Click the card to open the agent's page. Mach Studio keeps the agent up to date from here on.
Sign in
Each agent has an Accounts section on its page. A new account appears when you turn the agent on.
- Click Sign in on the account row.
- Choose how to sign in. Continue with your existing plan is the recommended option: it uses the subscription you already have, with no key to manage. The alternative is an API key, billed per token to your API account.
- Finish signing in in the window that opens. Mach Studio checks the login automatically when it completes, and the row shows the email you signed in with.
Codex CLI signs in with your ChatGPT account. For Claude Code, signing in to your own Claude account is optional: it runs on Mach Studio's models until you do.
Sign in to OpenCode
OpenCode needs no sign-in at all. Turn it on and it runs on Mach Studio's models right away. If you would rather use your own provider keys, click Sign in on its account row, choose OpenCode login, and click Continue. A terminal opens inside the dialog: pick a provider, then paste its API key or follow the link it prints. Add as many providers as you like.
Using an API key instead
Pick the API key option in the sign-in dialog, paste your key, and click Save key. The key is encrypted by the system and kept on this computer. Mach Studio passes it to the agent when that account runs, and nowhere else.
Start a chat
Open a new chat, click the model picker in the composer, and choose the agent under Harness. Everything else works the way it does for the built-in agent: the same sidebar, projects, and permissions.
Next: Multiple accounts or Switch agents and models.