Google has been pushing a lot more functionality into Photos as of late, even after it sunset its most popular feature by far. Check your app today: if the odds are in your favor, you might see a new entry on the bottom navigation bar. Don't get too excited though, it's just a direct link to some of the app's less obvious social features.
The new "Sharing" tab will show off the new uploads and likes from contacts that have shared with you. We saw hints of it a few weeks ago, and oddly, the iOs version of the Google Photos app has already had this feature for some time. We're seeing it active in about one out of ten Android Police team members; some who saw it previously have subsequently seen it disappear, so the Sharing tab may still be in testing.
Based on what we've seen so far, the new tab seems to be a server-side switch, so there's no need to hunt down the latest version of the app. If you do see the sharing tab and don't find it particularly useful, well, no one's making you tap it I guess.