While people who want to play XCOM: Enemy Within on the PC and Mac will be able to just download the $30 expansion as DLC, Xbox 360 and PS3 players won’t have that convenience.
According to an employee at XCOM developer Firaxis Games, the expansion’s file is too big for a console download. Instead Enemy Within will only be available through the new retail Commander’s Edition, which includes XCOM: Enemy Unknown and the Slingshot and Elite Soldier content packs as well as Enemy Within.