BioShock Infinite. The free weekend kicks off on Friday, March 8, starting 12:00 GMT and lasting until 23:59 GMT on Sunday, March 10.
A variety of multiplayer events will go down throughout the weekend, starting with "Rockstar Friday" when developers from the New York outfit will be online and competing in games of GTA IV: Episodes from Liberty City, Max Payne 3, Red Dead Redemption and Midnight Club LA. Other multiplayer events for games such as Halo 4, Borderlands 2, Tomb Raider, FIFA Ultimate Team, Forza Horizon, Far Cry 3 and Assassin's Creed 3 will also take place.
A Microsoft representative has confirmed with Joystiq that this is for the UK only.