Stolen from GAF:
https://www.youtube.com/watch?v=Pjh1Uo_xaSQ&feature=youtu.be&t=11170
"The new leadership team made the decision to invest in backwards compatibility about a year ago, they emulate the full 360 hardware level and it's running the OS, frame by frame performance, Xbox Live thinks you're on 360 so you can play with people who are on 360, Xbox One sees it as an Xbox One game so that's why Xbox One features work too, emulator runs exactly the same for all games unlike original Xbox emulation on 360 where emulation didn't scale well and they had to 'shim' on a title by title basis, emulator will be tweaked if any issues are found as they bring more games over, for 3rd party games they just need permission from publisher and then they'll run them through a QA test, Kinect games won't work, currently figuring out how to do multi-disc games."
