Unreal Engine 4.9 was released yesterday with DirectX 12 now supported as an experimental feature. If you are using Windows 10, you can try it out by running the engine with “-DX12” on the command line.
Microsoft’s engineers added support for DirectX 12 to UE4, and we have worked with them to integrate their changes into 4.9. The feature is still new and is considered experimental. DirectX 12 offers a much lower-level rendering API that is more efficient and allows for rendering commands to be submitted in parallel across many threads, a feature inspired by console rendering APIs. Going forward, we’ll continue to improve support for DirectX 12 and look for ways to leverage the new API in upcoming versions of the engine.
Source: Unreal Engine