Google has not graced us with a blog post or changelog to detail exactly what's different this time. So far we've spotted a new button for joining communities that pops up at the bottom of the screen, as well as a gear icon for accessing community settings. In your location list, you can now press the three-dot button to get directions or send a message to any contact. That's much better than the hidden swipe gesture we had before. There was also an odd text select bug in the last version that made the action buttons invisible, but that appears to be fixed now.
The APK is signed by Google and upgrades your existing app. The cryptographic signature guarantees that the file is safe to install and was not tampered with in any way. Rather than wait for Google to push this download to your devices, which can take days, download and install it just like any other APK.
File name: com.google.android.apps.plus-220.127.116.11692696-413339292-minAPI19.apk.
Version: 18.104.22.168692696 (413339292) (Android 4.4+).