September’s Games with Gold have been announced just as August begins to draw to a close. The Deer God and Tomb Raider: Definitive Edition are the free Xbox One games for the month and Battlestations Pacific and Crysis 3 are the free Xbox 360 games.
The Deer God will be available for the entirety of September while Battlestations Pacificwill only be free from September 1 -15. Both Tomb Raider: Definitive Edition and Crysis 3 will become free on September 16; however, Crysis will only be available until September 30 while Tomb Raider will remain free until October 15. Remember that all Xbox 360 Games with Gold will be become backwards compatible in the future so be sure to add them to your account even if you no longer own a Xbox 360.
Source: Major Nelson