@whatsausername3 Likely by the end of 2015.
— Phil Spencer (@XboxP3) March 21, 2015
He also added that the combined market of the PC and Xbox One immediately gives game developers access to a lot of DX12 gamers.
@Xone_br33 @BuckGamer Obviously studios will do what is best for them. DX12 across Xbox1 & Win10 will give devs a lot of DX12 gamers.
— Phil Spencer (@XboxP3) March 21, 2015
Source: eTeknix