The new Apple iMac Pro will be fitted with Radeon Pro Vega graphics solutions. Information published by Apple reveal more details.
You guys know that R9 Fury and Fury X had either 4096 cores (64 CUs) and 3584 cores (56 CUs). AMD likely will do the same with Vega, as confirmed by Apple iMac Pro specs and this is actually confirmed at the Apple website.
The new iMac will be fitted with Radeon Pro Vega 56 with 8GB HBM2 memory or Radeon Pro Vega 64 with 16GB HBM2 memory. The model numbers seem to be referencing the NCU count, which means 56x64=3584 cores and a full 64x64=4096 shader processors for the Radeon Pro Vega 64.