I assume (and this is a big assumption) that the US government will be focused on limiting access to the latest model, not necessarily everything smarter than Fable 5. Having access to the frontier model from a year ago (Sonnet 4.7-ish) wouldn't really help you from a cybersecurity perspective.

I think there's a world where the US funds development of the next model in exchange for exclusivity, at which point they could "release" the previous version from that exclusivity.