macOS runner profiles have offered a single machine shape since launch: 6 vCPU / 14 GB. There is now a second, 12 vCPU / 28 GB, running on M4 Pro hardware.
Pick it when you create or edit a macOS profile. The 6 vCPU shape stays the default, and existing profiles keep the shape they were created with.
Learn more in the runner profiles documentation.