I'm sure there is also a lot not on the Top500. I've got enough AMD MI300x compute for about 140th position, but haven't submitted numbers.
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Historically, those workloads and users were leading indicators of certain types of things. I don't think that's true anymore. In fact, I wonder if this is mostly a story of the government agencies not being able to compete with the private sector for NVIDIA gpus.
Companies like CoreWeave have deployed so many giant clusters (and growing), it is insane. Their IDLE compute is larger than most of the supercompuers out there.
Of course, they aren't on the list either.