Anandtech has a story about AMD moving away from Mantle, encouraging support for Vulkan and the upcoming Direct X 12. It’s not really the end of the world, though, as Vulkan, which is developed by the Khronos Group (the team that manage OpenGL), is actually based off of Mantle, meaning the transition should be fairly smooth. Launched in 2013, Mantle was meant to give 3D games access to very low-level instructions, meaning faster rendering.
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.
I’d really love for there to be more traction of cross platform APIs like this, to reduce the reliance on Microsoft Windows for PC gaming. If you look at the market share for different PC platforms, the landscape is very different from five years ago, with so many more games to choose from on OS X and Linux. Having a popular powerful platform-agnostic graphics language should help us see some AAA titles on SteamOS as well as Windows.
You can read a bit more about the stat of Mantle in Anandtech’s R9 Fury X graphics card review.