The Pentagon does this kind of thing all the time. It's just usually not this official.
This is not the government saying they're going with a different vendor, it's the government saying everyone has to choose to either have federal contracts or Claude, they can't have both.
The difference with Anthropic is it's open and above board instead of the customer telling a company "You can't sub with those guys or you won't get the contract."
The impact of this is far more than just DoD procurement, which is already enormous.