Run Claude Code agents in parallel, and merge the best one

By hand, with git worktree

1. For each agent, make a worktree on a branch of its own: git worktree add ../api-lane-1 -b try/lane-1.
2. Start claude (or codex) in each worktree's folder, in a terminal of its own, and give each the same task.
3. When they're done, compare with git diff main...try/lane-1, run your tests in each worktree, and merge the one you like. git worktree remove ../api-lane-1 tidies up.

Each agent runs as you, though: it can read and change anything you can, not just its worktree. With one agent you're watching, that's usually fine. With several running at once, it's worth containing them.

With Parallex: Fleet

1. On an agent workspace's page, choose Start a Fleet, or run parallex fleet run in Terminal.
2. Give it the task, the repository and how many lanes; lanes go round the agents you choose, Claude Code or Codex. A check command, like npm test, and caps on turns and budget are optional.
3. Watch the lanes live. Each works in its own git worktree and branch, sealed so it reaches its worktree and its own copy of its agent's home, and nothing else of yours.
4. When they're done, each lane's work is committed on its branch, the check runs in each lane's seal, and one is suggested: passing the check first, then the smallest diff, then the fastest.
5. Pick one and merge it: its work becomes one commit of yours, with the task as its message. Keep the other branches to look at later, or remove them.

What it costs

Fleet is part of Parallex Pro. Its lanes run Claude Code and Codex with your own sign-ins, so each lane costs what that run costs on your plan or account, as if you'd run it yourself. Parallex shows Claude Code's own estimate for each lane: an estimate, not a bill.

How many lanes

Parallex suggests a number for your Mac's memory, three on a Mac with 16 GB, between 2 and 6. More than 6 is possible from Terminal when you ask for it.

Sealed, not a virtual machine

Each lane runs the way an agent workspace runs its agent: under the macOS sandbox, with the same kill switch and network proxy. It's not a virtual machine: it's your Mac, with each lane allowed to reach only its own worktree and its own copy of its agent's home.