Nvidia is testing Rubin Ultra at 192GB and stepping back from HBM4E to HBM4.

TrendForce reporting via Tom's Hardware says prototype variants run 192GB or 256GB, down from the announced 288GB, with some configs using fewer than 16 stacks and substituting HBM4 for HBM4E. Driver is tightening HBM supply across SK hynix, Samsung, and Micron. At GTC 2025 configurations up to 1TB of HBM4E were on the table. Capacity planning consequence: a model that fits on four high-memory GPUs may need six or eight lower-memory ones, dragging along power, rack space, interconnect, and per-GPU licensing.