Apple has taken the first steps toward completely killing OpenGL and OpenCL in Mojave in favor of its own Metal technology.
Buried in the developer's documentation section, Apple made the declaration that it is starting a "grace period" from transitioning away from the older technologies.
Of the older graphics technologies, Apple says that:
Deprecation of OpenGL and OpenCL
Apps built using OpenGL and OpenCL will continue to run in macOS 10.14, but these legacy technologies are deprecated in macOS 10.14. Games and graphics-intensive apps that use OpenGL should now adopt Metal. Similarly, apps that use OpenCL for computational tasks should now adopt Metal and Metal Performance Shaders.
Metal is designed from the ground up to provide the best access to the modern GPUs on iOS, macOS, and tvOS devices. Metal avoids the overhead inherent in legacy technologies and exposes the latest graphics processing functionality. Unified support for graphics and compute in Metal lets your apps efficiently utilize the latest rendering techniques.
Given the news, it is just a matter of time until older apps using these technologies will no longer function — but they will still work for at least a year without updates. Apple also says that active development has ceased on OpenGL and OpenCL on the Mac, and the API's will only get "minor changes" going forward.
The move comes as no surprise. The OpenGL version on macOS High Sierra has been stuck at the version 3.3 that was released in 2010. The current version of OpenGL is version 4.6, released in 2017.
The Kronos group maintains the OpenGL standard. In February, the Khronos group released open source tools that allows Vulkan, a 3D graphics API, to work on iOS and macOS.
The move was intended to make it easier for developers to port games to Apple's hardware from other platforms, while still taking advantage of technologies like Apple's Metal graphics API. It isn't clear where the effort stands at present, however, given the deprecation of OpenGL.