The legacy of AMD's Mantle project lives on in those two APIs. Mantle will remain supported for some time but future AMD video cards will no longer get optimizations for the small number of Mantle-supported games.
"In discussing the performance results of the R9 Fury X with Mantle, AMD has confirmed that while they are not outright dropping Mantle support, they have ceased all further Mantle optimization. Of particular note, the Mantle driver has not been optimized at all for GCN 1.2, which includes not just R9 Fury X, but R9 285, R9 380, and the Carrizo APU as well," the site explained. "Mantle titles will probably still work on these products—and for the record we can’t get Civilization: Beyond Earth to play nicely with the R9 285 via Mantle—but performance is another matter. Mantle is essentially deprecated at this point, and while AMD isn’t going out of their way to break backwards compatibility they aren’t going to put resources into helping it either. The experiment that is Mantle has come to an end."Via: PC Gamer