Git worktree
Also called worktree, git worktree add
A second working folder for the same git repository, on its own branch, so 2 agents or tasks never edit the same files.
A git repository normally has one working folder, so 2 people or 2 agents working at once would be editing the same files. A worktree adds another folder, checked out on a different branch, that shares the same history. Changes in one don't touch the other until you merge.
That's what makes it safe to run coding agents side by side. It doesn't make it cheap: each agent still draws on your usage, and each finished branch is another diff to review.
For example
One agent fixes a billing bug in a worktree on its own branch while another writes tests in the main folder; neither touches the other's files.
Put it to use
Where you'll meet git worktree in ChatGPT, Gemini and Claude, how to use it there, and the mix-up most people make.
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