In a series of tweets, Spencer answered a range of fan questions about the new feature, which is currently in testing for Preview members and is scheduled to roll out for everyone this fall.
Among other things, he talks about bringing Microsoft's entire lineup of first-party Xbox 360 games to Xbox One via backwards compatibility, and also spells out some of the challenges, including licensing and save games.
He also teases that the Fable Trilogy--which includes Fable, Fable II, and Fable III--will be one of the Xbox 360 games supported on Xbox One by way of backwards compatibility.
Check out some of the questions and answers below. Not that Spencer refers to backwards compatibility as BC.
@CameronMines Some games, racing is most difficult, can have licensing issues (songs, logos etc) but we want to support BC completely.