I don't think something like Graviton would come close to half their opex. Ampere, linked elsewhere, made a competitive chip with just half a billion in total

I don't think something like Graviton would come close to half their opex. Ampere, linked elsewhere, made a competitive chip with just half a billion in total funding, and most of that was to scale up after the prototypes were built. Who knows, though. Nvidia's R&D expenses skyrocketed over the last five years and maybe Grace is a large part of it.