ID@Xbox developers now have access to Unreal Engine 4 tools through the subscription program announced by Epic Games back in March 2014. Previously, the program was catered to Xbox One developers. Now it has been made available to participants in the ID@Xbox initiative. UE4 is a middleware toolset designed to improve and accelerate development efforts by providing smart scripting tools, material editors, and animation systems. Developers can apply for a subscription on the Unreal Engine website.
Source: Xbox Wire