Another sibling thread already called this out, but mentioning here: it's not "USA only", it's "US citizens only" (and I'm not entirely sure how dual-citizenship interacts with this, but I assume you can't sell to them, either, since they are by definition also foreign nationals). A private company only being able to do business with folks they can verify are solely US citizens (who themselves are also willing to submit verification of said citizenship to a private company), has a relatively small pool of potential users.

And so if this policy holds, Anthropic has functionally had Fable killed by government intervention, and in a logically consistent world, this would imply all other US-based AI labs may also never exceed existing (read: Opus) capabilities.

What interesting times we live in, indeed.

Regarding the dual-citizenship, you are wrong to assume that. To US government you are US citizen and that is all that matters, even if you have 5 different citizenships government and justice system don't care, you need to follow the US laws and can't cherry pick what you want. Regarding users, for any of this big 3 (Alphabet, Anthropic, OpenAI) only important customers are enterprises, not individual users.

It kills their entire Enterprise market which is a far bigger deal than just consumer KYC headaches

I don't think so, most of enterprise customers are US based companies. They will basically give Mythos to US citizens in R&D while others will use Opus. I hope this is not the actual intent.

You think Anthropic will ask all their enterprise customers to provide passports for all their employees and then setup individual Claude accounts for each and every employee to gatekeep access to Mythos? Because a plain ole api key no longer cuts it

How many entreprise customers that aren't in the defense sector currently have R&D departments entirely composed of US citizens?

And what does it mean for indirect access to the models, through say agents working off ticket systems.

The problem here is that the valuations of these AI companies was based on the fact that they'd keep improving models. A company that just serves the latest Opus isn't worth trillions.