http://news.xbox.com/2014/05/xbox-delivering-more-choices
At the bottom:
**Free Games Offer: For paid Gold members only. On Xbox One, active Gold membership required to play free games you’ve downloaded. Must download titles during designated window. Kinect and/or hard drive required for some games.
Seems it will be exactly like PS+ now in this regard.
This should result in some more recent games.