Release notes here!
This one is mostly about the new architecture to support “External Data” that modders can store with various parts of the gamestate. This is obviously useful for data you want to persist across saving and loading the game, but even during normal operation it’s nice to be able to store data directly on ships (for example) so you don’t have to keep some kind of external dictionary and all the lookup-overhead that can mean.
It’s also set up in such a way that many different mods written by different modders can coexist without anyone stomping on anyone else’s data.
There’s also a key addition in the ways you can add ships to a control group. Actually, it appears that the previous way of adding ships to a control group may not have been working anyway. Which made the recently-added Rally command less useful than it could be.