Phil Spencer, ‘the head of Xbox’, just announced at the E3 2015 Microsoft conference that backwards compatibility is coming to Xbox One. Head of Engineering Mike Ybarra then showed off Mass Effect 1 running on the console and states that games will run exactly the same, but better as they will be able to take advantage of Xbox One features like multiplayer and screen sharing.
No mention as to when this change will be added but it’s a feature that Xbox fans have been clamoring for and it appears Microsoft put the work in to making sure everything works right.