Games With Gold is actually live now and if you are paying for Xbox Live Gold you can get Fable III for free up until June 30.
Microsoft will release new Games With Gold downloads on the 1st and 16th of each month. The Games With Gold program ends on December 31, 2013, which means Xbox Live Gold members will get thirteen free games. Unlike PlayStation Plus, these games are not rentals and tied to an Gold subscription. These downloads are yours to keep as long as you download it during the half-month window when it is free.