https://www.gamespot.com/articles/cuphead-passes-3-million-sold-on-xbox-one-and-pc/1100-6461114/

Cuphead, the gorgeous and difficult Xbox One and PC indie game, has reached an impressive new sales milestone. StudioMDHR's game has now sold 3 million copies. This is up from 2 million as of December 2017 and 1 million after its first two weeks back in September.

"It's hard for us to express just how appreciative we are to everyone who has played and enjoyed our niche little run & gun game with the wacky rubber-hose characters," the developer said in a blog post (via Gamasutra).