The 20-year-old will join up with the Potters in January following successful talks between the two parties.
Manager Mark Hughes told the club's official website: "We've put a lot of work into this deal, and I am delighted that we have managed to get the deal over the line.
"It's a good deal for us, because he is a very good young player who boasts a lot of talent as well as a lot of potential too. I've known of him for a couple of years now. He burst on to the scene for the United States at the age of 17 and everybody has paid attention to him since."
The USA international has scored twice in 17 appearances for the national side.