This one contains many visible changes but mainly a lot of behind-the-scenes changes in preparation for the upcoming "Vengeance of the Machine" expansion (more details to come on that fairly soon).
Some of those changes are peeking out from behind the curtain: the AI's Guardians are now becoming another source of variety between games (i.e. Replay Value). So we're revising the existing guardians to be more notable so that you'll care whether the AI rolled Laser Guardians or Artillery Guardians or Special Forces Guardians (or all three) or whatever. Right now there are only 19 guardian types to choose from (Tachyon Guardians are separate) so there's something like a 40% chance in any given game that one guardian type will be in the initial 3 picks for both fo the AI players. That's not too bad, as far as variety goes, but one goal of the expansion is to add substantially to that guardian variety. We'll see!
Other notable changes include some significant follow-up buffs to the Enclave after its recent re-imagination, fixes for some longstanding (mainly edge-case) AI behavior quirks, and an increase in the number of rolls of tissue paper used to armor Advanced Factories.
Update: 6.027 hotfix to get some for-next-expansion stuff back behind the scenes (sounds of something being hit with a cane). "Shoo! Shoo!"
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.