Xbox One has a backwards compatibility feature that developers can opt into which allows Xbox 360 games to be played on the Xbox One. However, this also extends to the DLC for a game if the developers allow it.
Head of Xbox Phil Spencer replied to a tweet asking how DLC would work via backwards compatibility by stating "We are working on a clear description of how DLC will work. It should work as expected."
Head of Xbox Phil Spencer replied to a tweet asking how DLC would work via backwards compatibility by stating "We are working on a clear description of how DLC will work. It should work as expected."
