Me and a friend live long distance and want to play fable and halo together co-op but I have a one and she a 360. So I was wondering if the backwards compatibility would let us play multiplayer. Any answer is appreciated
Absolutely. An Xbox 360 game running on the Xbox One has full multiplayer support. From the Xbox One Backward Compatibility FAQ:
Can I do multiplayer gaming with friends who are playing the game on Xbox 360 or Xbox One?
Yes. For games that offer multiplayer gaming, you'll be able to play with others who own the title on Xbox 360.