Assassin’s Creed II will be free on Xbox Live for Gold members until July 30 under the Games with Gold program.
https://www.youtube.com/watch?v=Xt4YBjsP2hQ?modestbranding=1
Announced at E3 2013 (watch the E3 announcement trailer below), the “Games With Gold” deal would be offering two free games each month. The first free July game was Defense Grid: The Awakening, a tower-defense title.
https://www.youtube.com/watch?v=sz6Qwaels_Y?modestbranding=1
In related news, Assassin’s Creed content is currently discounted on Xbox Live. More details on it is at Major Nelson’s blog.