https://developer.apple.com/macos/whats-new/

Deprecations and Removed APIs

Periodically, Apple adds deprecation macros to APIs to indicate that those APIs should no longer be used in active development. When a deprecation occurs, it’s not an immediate end of life for the specified API. Instead, it is the beginning of a grace period for transitioning from that API and to newer and more modern replacements. Deprecated APIs typically remain present and usable in the system for a reasonable time past the release in which they were deprecated. However, active development on them ceases, and the APIs receive only minor changes to accommodate security patches or to fix other critical bugs. Deprecated APIs may be removed entirely from a future version of the operating system.

As a developer, avoid using deprecated APIs in your code as soon as possible. At a minimum, new code you write should never use deprecated APIs. And if your existing code uses deprecated APIs, update that code as soon as possible.

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. For information about developing apps and games using Metal, see the developer documentation for Metal, Metal Performance Shaders, and MetalKit. For information about migrating OpenGL code to Metal, see Mixing Metal and OpenGL Rendering in a View.