Albeit all X399 motherboards are compatible, ASUS deems in necessary to update the Zenith II serries towards an Alpha model with an even stronger VRM design.

Although it continues to maintain 16 phases of power, this Alpha version uses the Power-Stage Infineon TDA21490 instead of the TDA21472 used in the original model. This allows the maximum current per phase to be raised to 90A, compared to the original 70A. Threadripper 3990X likely is used with lots of memory, think 128 GB and 256 GB and that does require proper power stages for the higher frequencies. 

Otherwise the motherboard is identical to the original model. It still supports 8 ram modules in Quad-Channel with frequencies up to 4733MHz, 4 PCI-E 4.0 x16 slots, 10Gb/s Ethernet, Wi-Fi 6, maintains its OLED display. The audio adopts "ROG SupremeFX" of S1220 + ESS9018Q2C. At this time, no sales announcement has been issued for this product in the domestic market. The original model costs $850.