The EHP is a combination of a main die, housing a large number of CPU cores, a large GPGPU unit, and an interposer, which connects the main die to 32 GB of HBM2 memory that's on-package, and is used as both main-memory and memory for the integrated GPGPU unit, without memory partitioning, using hUMA (heterogeneous unified memory access). The CPU component consists of 32 cores likely based on the "Zen" micro-architecture, using eight "Zen" quad-core subunits. There's no word on the CU (compute unit) count of the GPGPU core. The EHP in itself will be highly scalable. AMD hopes to get a working sample of this chip out by 2016-17.
Source: TPU