Apple announced the Metal API is coming to the next version of OSX due out this fall. Odd choice. Wonder if that means they're not going to support Vulkan.
Metal is a low level api, like Mantle, Vulcan and D3D12. I've read some posts on this forum that suggest it's missing some good features from those other APIs. It doesn't sit on top of OpenGL. It's a separate API that's available only on iOS and OSX. Apple handles drivers for you, so if you have OSX 10.11 when it's out, or iOS 8 or higher, you have Metal support. Not sure what the hardware cutoff will be, or if they do feature levels for Metal.
Currently with the technology behind Macs and the way Overwatch runs it's just too challenging for us at this point to support it," Kaplan said. "Our focus right now is entirely on PC, Xbox One and PlayStation 4.