In a blog post, Bryan Langley from Microsoft has written that the final version of the just-announced Windows 10 will come with DirectX 12. To be clear, the current technical preview that's available does not come with DirectX 12.
In the blog post, Langley points out that Microsoft has also been working with Epic to create a DirectX 12 branch in the Unreal Engine 4 GitHub repository. If you've been granted a pass to the DirectX 12 Early Access program, you can already kick off your development for the new API on Windows 10.
The screenshot provided above is of Epic's UE4.4 Landscape Mountains demo running on Intel Haswell graphics hardware. (Yes, we would have liked a higher-resolution image too.)
What makes DirectX 12 so interesting is that it allows developers to code much closer to the hardware, resulting in reduced overhead and therefore improved performance. This is similar to AMD's already-available Mantle API, which was designed from the ground up to deliver better performance than DirectX 11.
Of course, it's all jolly good that Windows 10 will support DirectX 12, but that doesn't really matter if the hardware support isn't there. Well, the good news is that back in March at GDC, both Nvidia and AMD confirmed that DirectX 12 will be supported on all of the current hardware, which for Nvidia are Fermi-, Kepler- and Maxwell-based GPUs and for AMD is its GCN hardware. Whether the two companies will live up to their promises remains to be seen, but we're going to remain hopeful.