Microsoft has confirmed that the Xbox One's backward compatibility feature will fully supports Xbox 360 DLC.
However, as with full game titles, it is up to publishers to give Microsoft the go-ahead for DLC to be playable on Xbox One according to the Xbox Support Twitter account.
@SomberShadowI Hey there, good question! While the console allows it, DLC of specific titles is up to the publisher 🙂 ^GC
— Xbox Support (@XboxSupport3) June 22, 2015
Xbox 360 multiplayer, cloud saves, and achievements are all features which are supported by the One's backward compatibility technology. The feature essentially tricks the Xbox One into by emulating a virtual Xbox 360 environment on the system. Physical discs are installed when you insert the disc, while digital games simply need to be re-downloaded.
Though currently limited in scope, Microsoft plans to roll-out the feature to all Xbox One users this autumn and 100 titles are scheduled for support by the end of the year. Xbox One preview program members can already avail of backward compatibility.
21 titles including Mass Effect and Super Meat Boy are currently supported by the Xbox One's backward compatibility.
