The X399 motherboards feature eight DDR4 memory slots and offer three PCI Express x16 slots with full x16 wiring thanks to 64 lanes:
The other characteristic feature of these boards is that they feature up to three PCI-Express 3.0 x16 slots with full x16 wiring, taking advantage of the 64-lane PCIe root complex, with the fourth slot splitting away x8 lanes from the third slot. This is unlike Intel, where after you've spend $999 on their 10-core processor, you can only run up to two slots at x16.Three products were spotted by TPU, including the ASRock X399 Fatal1ty Gaming 9, ASRock X399 Taichi and GIGABYTE X399 Aorus Gaming 7. You can view more photos and specs over here.