Thanks for sending that over! I'll post back with my results very shortly. I have not tried switching build platforms with that many assemblies, no -- I wound up culling the number of assemblies to more like 9 before doing that, and it was basically as fast as ever. The bulk of the platform-switching time is shaders and materials and other non-C# assets from what I can glean, so if there's an extra 10% (or whatever) time required to recompile all of the C# code compared to non-split assemblies, it would still be well worth it. For me in general, I tend to use Advanced Builder to just have it compile all of the platforms in sequence while I get a coffee or catch up on reading documentation or whatever. For asset bundles I have a specific set of code I put together myself that also profiles how long it takes (same time for lightmap baking), but the asmdef stuff doesn't affect those at all since they don't require platform context switches. On a totally random side note, I do wish it was possible to re-bake just all the reflection probes from code. For my scenes, typically static reflection probes are reflecting what the other static reflection probes are reflecting, which means that I have to do a normal lightmap bake pass plus reflection probe bake, then a second reflection probe bake manually from the lighting window. Not a crisis, but it's been interesting.