Start a session

Start a session to run a harness on a task in your project. Make sure you have installed a harness first.

Open the form

Any of these opens the “New session” form:

Click + next to Agents in the sidebar (“New agent”).
Run tyrn: new session from the command palette.
Choose New Agent Here on a worktree’s menu.

Fill it in

Field	What it does
Role	Optional. Start from a saved role.
Harness	Which agent to run. “Install more harnesses…” opens the harness list.
Name	Optional, up to 80 characters.
Worktree	“This workspace (branch)”, an existing worktree, or “New worktree…”. See Run sessions in parallel.
Inference	“Native: uses `<Harness>`’s own sign-in”, or Tyrn router. Connect provider takes you to settings.
Model, Effort	With Native, type a model or keep the harness default, and pick the effort. With Tyrn router, pick from the models you connected.
Plugins	Choose which plugins to load for this session. Add plugin adds one.
More options	Advanced harness settings and the Subagents to load. Collapsed, it shows a summary such as “default settings · 1 subagent”.

The New session form with Role, Harness, Worktree, Inference, Model and Effort fields and a Start button.

Some harnesses can’t use the Tyrn router. The form then says “<Harness> does not support Tyrn router inference” and gives the reason. The form can also show notes about how completely a harness is isolated from your global setup.

Start

Click Start, or press Enter. The session opens in a tab and appears under Agents.

Other ways to open a session

tyrn: open terminal opens the first installed harness.
tyrn: open shell terminal opens a plain shell, shown as “Shell”.
tyrn: attach session attaches to a session that is already running.

Change settings later

Use Restart with New Settings… on a session to restart it with changed options.