The first beta of Unity 2018.3 was just released and can be downloaded here or from the Unity hub. By far and away the star of the 2018.3 release is the new ability to nest prefabs, instead of forcing you to organized your prefabs in giant monolithic structures or tiny granular detail, you can now mix and match, composing prefabs out of other prefabs. If you are interested in learning more about this new feature, be sure you check out the dedicated Unity page on prefabs.
This release also included several other improvements including:
- Improved Prefab workflows
- Terrain System Improvements (Preview)
- Isometric 2D Tilemaps
- 2D Animation V2
- High Definition Render Pipeline (Preview)
- Memory Profiler (Preview)
- New Default Scripting Runtime
- Editor Improvements
Additionally there are an absolutely huge number of fixes and improvements in this release. For full details be sure to check the complete release notes for details.