I am fairly certain that the existing UE crowd manager uses GPU flocking.
Chris Murphy showed us a demo of something else recently though that I think was compute accelerated for large crowd skeletal animation. I think it’s used in fortnite single player to help with animating large numbers of enemies, it’ll dynamically switch from compute to CPU as zombies break from the proscribed animation or something. That is probably 4.23 at least. Might be worth asking him on Twitter about it: https://twitter.com/HighlySpammable