Vulkan is Here
NOT a successor. It's a very different beast. It's frequently described as a "low-level" API, but "explicit API" is more correct. It gives you control (and responsibility) for things that happen behind your back in OpenGL, e.g. semantics of sharing of resources between the CPU and the GPU, explicit separate access to many GPUs, explicit separation of command buffer building and submission etc.It will live side-by-side with OpenGL for the foreseeable future. It's just targeting the same general area (graphics using GPUs) and is standardized by the same folks (Khronos).