Is Mantle a Vulkan?
AMD’s Robert Hallock confirmed on a blog post that Mantle had, for the most part, been turned into the Khronos Group’s Vulkan API that would supersede OpenGL.
What happened to AMD Mantle?
Ultimately, AMD discontinued Mantle as a game API due to the similar aims DirectX 12 and glNext (later renamed Vulkan). AMD donated the Mantle API to the Khronos group, which developed it into the Vulkan API.