The Vulkan API has been brought to macOS and iOS, without Apple's involvement

The Vulkan API was initially designed to support all platforms, though sadly Apple didn't actively encourage its development, instead focusing on their Metal API. This lack of support has left games to run on the ageing OpenGL API on MacOS and OpenGL ES on iOS, leaving gamers and developers at a disadvantage when running their programs on these platforms.

This lack of support means that developers need to work on an additional version of their software to run on Metal to receive the same low-level optimisations as Vulkan, but now Kronos has released MoltenVK, a subset of Vulkan that can translate Vulkan calls to Metal calls, enabling Vulkan on iOS and Mac OS. 

MoltenVK came into existence thanks to Valve, LunarG and Brenwill Workshop, who together with Kronos created the open source SDK. Valve has already built a Vulkan update for DOTA 2 which offers an incredible performance boost in DOTA 2 on MacOS, which currently is only available using the OpenGL on Apple devices. Below you can see a graph which showcases up to a 50% increase in performance after moving to the Vulkan API on MacOS. 

Vulkan offers developers the opportunity to bring their existing games to MacOS without the need for an all-new Metal API version, allowing the same low-level API to be used across Windows, Linux and MacOS.