This one revamps the Dark Spire minor faction and does a balance overhaul on Starships, notably adding a long-requested new important capturable structure: The Advanced Starship Constructor.
For the Dark Spire:they should still be just as influential upon the galaxy once truly unleashed (in fact, more influential due to improved "what do I do now?" logic), but now they (probably) won't melt your CPU in the process. Previously you could wind up with 50k+ of the things if you really cranked up one of the vengeance generators, but now it's much better about concentrating spawns into a smaller number of more powerful units as the overall Dark Spire population increases.
For the Starships: the main combat and combat-support starships have had their caps halved, their cap-DPS reduced significantly (so individual DPS is the same or a bit higher), their metal/crystal/energy costs halved, and their knowledge costs slightly-more-than-halved. The result is a better deal but it's much less likely that you'll be able to get all the core firepower you need from just starships. This helps better emphasize the role of starships as a category: supplementary to fleet ships, and capable of some important independent operations, but not something that contests with the fleet ships category for the role of damage-dealing.
In addition, there's now a starship equivalent of the Advanced Factory so you can produce mkIV versions of many starship types (if you have the corresponding mkIII type unlocked). To top it off, Fabricators for the mkV versions of those starship types are now also on the list of possible experimental-starship fabs.
The release also has a few other changes, notably an increase to starting metal/crystal stockpiles. The difference is only a matter of minutes even at just-the-homeworld resource harvesting levels, but it does help the very early game drag less.
This is a standard update that you can download through the in-game updater itself, if you already have 4.000 or later. When you launch the game, you'll see the notice of the update having been found if you're connected to the Internet at the time. If you don't have 4.000 or later, you can download that here.