That's not a typo in the headline. This patch is not for the recently released Galactic Civilizations 3, but for the nearly ten year-old Galactic Civilizations 2. Released last Thursday, version 2.20 incorporates a number of community mods into the base game, as well as making tweaks to its already formidable AI.
As the forum post describes, there are changes to the game's tech tree, "AI value judgement" and more by users Gaunathor and MabusAltarn, as well as other tweaks - including lots of changes to in-game tech descriptions - from other long-time players. Stardock CEO Brad Wardell also says that the community "gave me a long list of areas where they thought I could improve the AI, which I used to dig into the now 10 year old AI source code base to implement."
Galactic Civilizations III left early access earlier this year and has been receiving regular updates of its own, including a revision of its diplomacy system at the start of the month. Adam's review of that game rightly noted at the end that updates were likely:
It’s also worth noting that GalCiv III will most likely be a better game in two, three, five and seven years than it is now. Currently, it’s neither a perfected version of its predecessor or a successful step in a radical new direction. So what is it? On a medium map (maybe large with scarce habitable planets if you fancy losing a couple of weeks), with a good mix of AI opponents, it’s a fantastic update to one of the best 4X games in existence. Whether that’s enough, only you can decide. Don’t be surprised if I’m revisiting in a couple of years to tell you it’s become something much more remarkable though.
While updates are standard practice these days, I still find something fundamentally delightful about developers going to patch their more ancient works.