Lightmap baking multi-threaded or via GPU?

[system]

They are working on GPU lightmapper:

Progressive GPU Lightmapper preview

GPU lightmapper is a preview feature. Preview means that you should not rely on it for full scale production. No new features will be backported to 2018.4, 2019.x or any of the following releases. We recommend using 2023.2 or later because the GPU lightmapper has reached feature parity with the CPU version at this point. The goal of the GPU lightmapper is to provide the same feature set as the CPU progressive lightmapper, with higher performance. We would like you to take it for a spin in the …

And on the progressive as well:

Progressive CPU Lightmapper

Dear beta users, The latest Unity beta (5.6b6) includes an experimental version of the new Progressive Lightmapper. We are super excited to bring this feature to you and hope that it will considerably improve the workflow of those of you who work with baked lighting. Preliminary docs: https://docs.google.com/document/d/18dN_KWdF52ou7NXgbqhdB36kVFEyfmojn_JlCeoLN9Q We still have a few features incoming (see below) and some bugs to iron out. At the same time please note that the release in 5…