Which APIs are being deprecated? [Inject] ComponentDataArray SharedComponentDataArray EntityArray BufferArray ComponentArray GameObjectArray ComponentGroupArray Edit: Removed TransformAccessArray from this list until we have a good alternative Why are they being deprecated? Usability is always at the core of Unity, and the simplicity of our APIs is a key part of that. But simplicity should never come at the cost of transparency, especially when performance is involved. We've recently identified some key performance problems with these APIs which are not immediately obvious from the surface. While they provide a neat and simple way to access your data, they abstract away the systems underneath them, which makes identifying bottlenecks and optimizing your code more difficult. It becomes more difficult to move to the low-level APIs when performance or control requires it. So simply put, they make it harder to learn how to use ECS to write fast code. A more detailed explanation can be found in this talk from Unite LA 2018: What are the recommended replacements for _Array? IJobProcessComponentData provides a simple way to iterate through and transform component data. You can also use ForEach in a main-thread ComponentSystem for added simplicity, but at the cost of performance and parallelization. IJobChunk and ComponentGroup.CreateArchetypeChunkArray provide more manual control, which may be necessary to solve certain problems efficiently. What are the recommended replacements for [Inject] ComponentGroup injection (injecting structs) is replaced by (Job)ComponentSystem.GetComponentGroup, ForEach, IJobProcessComponentData, IJobChunk, and manual chunk iteration. ComponentDataFromEntity injection is replaced by (Job)ComponentSystem.GetComponentDataFromEntity. Injecting other systems is replaced by (Job)ComponentSystem.World.GetOrCreateManager. Note: When converting the injection of a EntityCommandBufferSystem (formerly BarrierSystem), you must explicitly inform the EntityCommandBufferSystem of which JobHandle(s) to wait on before executing with EntityCommandBufferSystem.AddJobHandleForProducer. A well-commented example of this can be found in the HelloCube_06 sample. You can read about all of these APIs on the GitHub Documentation page. The repository also has Samples which show how these APIs are used. When will they be removed from the Entities package? All of these APIs will be marked as Obsolete in either release 0.0.23 or 0.0.24. At the earliest, they will be removed in release 0.0.25. What about my use case [x]? It's possible we've missed something, or that the new APIs aren't completely clear. Feel free to use this thread as a place to discuss your individual use cases and provide feedback.