Seems like some free Gears of War Judgment DLC popped up on Xbox Live during the long weekend. The DLC contains both the “Execution” mode and the new Haven map.
Execution mode has the players having to kill all members of the opposing team within a time limit, but finishing them off with an execution before they get back up. The DLC also includes the Haven map. Check out the screens below. Playing on the Haven map or in Execution mode will rack the player double XP, or triple if they already have the season pass, for a limited time.