Anthropic should just cancel the contract then. Draw the line in the sand, tell them "this is how our model works, take it or leave it." If their model is so good, and the pentagon just has to use it because it works so well for them, Anthropic is the one with the power here. Cancel the contract, cut the pentagon's access immediately, and let them come crawling back.
But, they won't, because they'd never voluntarily give up that sweet, sweet military contract worth many billions of dollars. They'll bend over and take it just like every other spineless company has, does, and will do.