https://support.circle.com/hc/en-us/articles/217972003
https://blog.circle.com/2016/12/06/spark-new-markets-app-messaging-and-bitcoin-changes/
"Circle is now more than ever not a consumer bitcoin exchange, and we will continue to focus resources on global social payments and future next-generation blockchain technology rather than devoting those resources to supporting the buying and selling of bitcoins directly.
Circle customers who currently hold bitcoin instead of US dollars, pound sterling, or euros may convert instantly to any of those currencies (depending upon availability in the customer's area). Customers who previously bought and sold bitcoin in the Circle apps may still sell, if they choose, by converting their bitcoin to dollars, euros, or sterling and then withdrawing the balance to their linked card or bank account. Once converted, the account will remain in dollars, euros, or sterling.
Consumers who seek to buy and sell bitcoin in the future may now leverage our new preferred partnership with Coinbase. Customers may still send their bitcoin to any wallet or exchange of their choosing, but Coinbase is our recommended consumer bitcoin exchange."
L-O-Motherfucking-L