Microsoft is going to offer customers who purchase a Xbox One from participating retailers during the 7th to the 13th of September a free game valued $59.99 or lower. This offer is only available in the US.
Some of the games that you have the opportunity to pick up during the promotion are Watch Dogs, Diablo 3, Titanfall and Plants vs Zombies: Garden Warfare just to name a few. The game must be a brand new disc-based unit.
Although it is limited to a maximum of one game, if you purchase either the Madden NFL 15 or the Forza Motorsport 5 or Xbox One with Kinect bundles, you can still get a brand new game on top of the said bundles as long as the value of the game is $59.99 or lower.
Source: Xbox Wire