With a full integration in Unreal Engine 4, Substance Engine makes the creation of next-gen textures a seamless experience for even the most ambitious of game developers. integration comes as a free plugin available for all Unreal 4 licensees.
That is what the email from Allegorithmic says.
What is does not say is, how to actually install it. You must have a github account linked to your UE4 account so the Allegorithmic Substance github page appears. Then you look for the dll files in the plugins folder branch, and download.
Download… and copy… where? Anybody?