It's actually split. The NVMe controller is in the M1 SoC, but the flash modules contain their own dumber controller and connect via PCIe in the back end (using

It's actually split. The NVMe controller is in the M1 SoC, but the flash modules contain their own dumber controller and connect via PCIe in the back end (using a custom protocol, not NVMe). Apple could and have put their SSDs in modules - that's how the T2 Mac Pro does it. They're still proprietary though, of course, due to the split design.