The full release notes are on the Arcen forums. This new prerelease includes a number of bugfixes including a couple of important tweaks to the new CoN expansion beta (which wasn't installing completely correctly in the last release, although there was a simple workaround). This new version installs just fine, and additionally adds a new Neinzul Regeneration Chamber unit that makes the Neinzul ships a viable choice for planetary defense, instead of just an offensive-only ship class. More updates to come soon, for AI War, CoN, and Tidalis!
UPDATE: Now 3.175 is out, as well -- same link above. That's probably the last new release for today. It alters the balance of the Youngling ships to a fair degree, as well as adding in the new Vultures and Weasels (Mark I-V on both).