Google is on an update spree for most of its apps, probably getting everything as ready as it could before the end of the year holidays. An update to Google+ rolled out yesterday, bringing the app up to version 6.9 and updating the look of the Notifications tab.
[Update: Full Changelog] Google+ 6.9 Introduces A Full Tab For Your Notifications [APK Download] was written by the awesome team at Android Police.
Source: Andriod Police