This one has a number of mod improvements, including some things for Sidekicks, and leveling up the Dyson Sphere sidekick in particular. The work of the Badger.
It also has a lot of experimental tooltip improvements that you can opt into from SirLimbo, and some updates to AMU. It also has a wide variety of bugfixes and improvements from Dismiss, most of which don't seem to be on the wiki quite yet, but should be before too long. Classic Fusion has also seen some updates to keep up to date with the core codebase changes, thanks to Puffin.