Can I run Hy3 on an RTX 5090?

No

Even its smallest file (4-bit (estimate), 168 GB) is more than an RTX 5090 can hold (28.8 GB usable): it needs 6 of them.

Files and context on RTX 5090

Each file of Hy3 (and of GGUF versions the site has analyzed), and how much context fits next to it, with the context cache in 16-bit or 8-bit.

Hy3 on other hardware

Popular models that run on RTX 5090

Assumes 90% of the card's memory is usable and at least 4K tokens of context for one conversation, with the context cache in 16-bit unless noted. Fits leaves at least 20% of that memory for context; Tight leaves less.