Largest GPU cluster at the moment is X.ai's 100K H100's which is ~$2.5B worth of GPUs. So, something 10x bigger (1M GPUs) is $25B, and add $10B for 1GW nuclear reactor.

This sort of $100-500B budget doesn't sound like training cluster money, more like anticipating massive industry uptake and multiple datacenters running inference (with all of corporate America's data sitting in the cloud).