How many macOS VMs can run at once?

Two. Apple's licence and its Virtualization framework limit one Mac to two macOS guest VMs running at the same time. Linux guests are not subject to that limit. The why kinhin exists page has the sources.

So a design that runs one VM per runner tops out at two parallel macOS jobs on one Mac, however fast the Mac is.

How kinhin gets past two

• Several runners in one VM. runners_per_vm runs more than one runner process inside a single Tart VM, so one VM can take several jobs. Size vm.cpu and vm.memory_gb for the sum of the jobs it will run. See Job density.
• Linux jobs in containers or Linux VMs. Linux jobs run in apple/container microVMs, Docker containers, or Tart Linux VMs. The two-VM limit applies to macOS guests only. See Runtimes.

The cap still depends on your Mac. Cores, memory and free disk set how many jobs fit at once, as described in How scaling works.

Next steps

• Quick start: From zero to a working fleet
• Install: Pinned versions, updates and uninstall
• Forge support: What has been run against a real server
• Why kinhin: Why most runners do one job at a time