IMO this is all just great marketing. The government needs to keep the hype for AI going as long it can cause so much of the economy and stocks depend on it now. Unless they have cracked RSA or something, no model warrants such a restriction, period. Mythos has already been used by the likes of Microsoft, Linux etc. If no big security gaps were found there, what is the government so afraid of?

I use Opus everyday on my code. It finds security gaps, but nothing outrageous, and that's coming from someone who writes code that is nowhere near weapons grade secure. It finds mostly things that are technically bugs, but virtually intractable for exploits. Often things I overlooked cause I was lazy, like not synchronizing access to a shared pointer etc.