Microsoft and NVIDIA has decided to release some information about DirectX 12 (and DirectX 11.3) alongside the launch of the Maxwell-based GeForce GTX 980 and GeForce GTX 970 graphics cards. Mostly, they announced that Microsoft teamed up with Epic Games to bring DirectX 12 to Unreal Engine 4. They currently have two demos, Elemental and Infiltrator, that are up and running with DirectX 12.
Moreover, they have provided a form for developers who are interested in "early access" to apply for it. They continually discuss it in terms of Unreal Engine 4, but they do not explicitly say that other developers cannot apply. UE4 subscribers will get access to the Elemental demo in DX12, but it does not look like Infiltrator will be available.
DirectX 12 is expected to target games for Holiday 2015.