Z390 will get an LGA1151 socket using the traditional DMI 3.0 chipset-bus (which basically is an x4 PCIe link lane up/downlink. Similar to the Z370 chipset, it'll have 24 PCI-Express gen 3.0 lanes.

Unlike previous architectures, the block diagram shows two CPU-attached M.2 NVMe slots, ... a Gen 5 x4 M.2, and a DMI 4.0 x8 chipset bus, along with an additional CPU-attached Gen 4 x4 M.2 slot.