Several Nexus 6 owners were a bit baffled to receive an OTA update rolling their phones back to Android 7.0 from Android 7.1.1. The initial thought was that there must have been some sort of huge security bug or some other bug that Google thought it necessary to downgrade phones. Google's response as to why they released the downgrade OTA was to keep everyone on the OTA update supported track. So the update was meant for those who were sideloading beta builds but was made available for all and is stated to be the version of Android you must be on to guarantee future OTAs. Google says if you wish to sideload your own updates feel free to stay on Android 7.1.1.
via Reddit