There has been much speculation about just how much improvement, if any that Direct X12 would add to the Xbox One, and after the Microsoft keynote speech at GDC15 it has been confirmed that the Xbox One will gain a 20% graphical boost from Direct X12. Head of all things Xbox, Mr (Cool As ) Phil Spencer stated that the Xbox One will benefit from a 20% GPU performance increase which is a staggering boost. Along with the news about Direct X 12, came the following news, rounded up by XboxWire:
apu in the x1 was designed around dx12 so a 20% increase is graphical output sounds about right and i remember reading something about older games may benefit from it too if developers decide to tinker with old games.