Madden 18 is getting a whole new engine, but it's not playable in 4K and HDR. At least not yet.
While it will support these features at a later date, they are not currently available in the review version that has been distributed to the press. The menus load very quickly, but there is no option for 4K or HDR in the settings.
Asked about 4K and HDR support, Madden director Rex Dickson told USgamer that PS4 Pro support will be added in a future patch, but would not reveal any further details.
In this case, "future update" is fairly ambiguous. It could be added before it launches next Friday, or it could be added in October. One way or another, though, it will not be available in the base version without a patch.
But when it does arrive, it's apt to look pretty great. I played it in 4K on Xbox Scorpio back at E3, and I was quite impressed by the bright colors—the sunsets really stand out in HDR—and the high-resolution textures.
Madden 18 is meant to represent the next major step forward for the series. In addition to (eventually) supporting 4K for the first time, it is shifting to the Frostbite Engine and adding Longshot—a brand new story mode.
We're currently in the process of downloading Madden 18 on the Xbox One so we can check on HDR support there as well. We've also reached out to EA to try and confirm whether 4K support will be available at launch [Update: It's not an option in the Xbox One version, either].
Madden 18 will be available for a limited time via EA Access on Xbox One starting August 17. It will be fully available to the public on August 25. Go here to find everything we know about Madden 18 so far.