Unity just released an experimental AutoLOD, a system for automatically creating LOD (level of detail) scenes and optimizing their performance. Once again, the entire thing is experimental, so expect warts and dont expect support. The extension requires Unity 2017.3 or newer as well as git-lfs and git-submodule.
Details from the Github page:
- LOD generation on model import with sensible defaults
- Project-wide and per-model LOD import settings
- Asynchronous, pluggable LOD generation framework
- Hierarchical LOD support via SceneLOD
Useful classes (for your own projects, too!)
You can learn a great deal more about AutoLOD in this blog post.