Xbox One will let users play games, even if they're only partially downloaded. The feature is similar to what Sony proposed during PS4's reveal event in February.
Polygon points out that all games must be installed to the hard drive on Xbox One, including games purchased on disc. Previously, Microsoft said that games could be played while they were still being installed on the console, but did not clarify if that would apply to downloaded games as well.
In a UI video, Sony revealed that you could begin downloading the single-player portion of a PS4 game first and play that while the multiplayer half downloads in the background. It remains unclear how Xbox One will implement their play-while-you-download strategy, but with games potentially ballooning up to 50GB, we're glad to have that option.