I've also been under the (possibly incorrect) impression that the majority of Circle's dealings are with exchanges like Coinbase — parties who are probably willing and able to play some inside baseball in terms of dealing with duration mismatch and waiting out the feds.

Edit: Yeah, they are very strict with who they interact with — individuals cannot exchange their USDC for dollars directly with Circle: https://www.circle.com/en/legal/acceptable-use-policy.