http://gamerant.com/xbox-free-games-with-gold-january-2016/Jan games for XB1/xb360
XB1:
Killer Instinct Season One Ultra Edition: This includes all characters and they will not need to be purchased individually. The game will be available from January 1st and last all month.
Zheros: A 3rd person fighting game via the Id@xbox program, Zheros blends single player gameplay with a variety of customization and hilarious player animations. It will be available from January 16th through February 15th on Xbox One.
360:
DiRT Showdown: Will be available from January 1st - 15th for all Gold subscribers
Deus Ex: Human Revolution: Available from January 16th-31st.