The Nexus 6 wasn’t expected to get any further updates. The device was launched late 2014 and received both two years of software updates and three years of security updates, as promised. Support ended back in October 2017.
Nonetheless, people are now seeing an OTA to build N8I11F. This is still Android 7.1.1 Nougat and the security patch is still October 2017, but the baseband has been updated.
The factory image and OTA image are both up and imply that the update was related to T-Mobile, though everyone seems to be getting the update. It’s likely that the baseband was modified for an improved experience on the carrier.
The benefit of this update is that, for those still stuck on Android 7.0, this update will finally get you to 7.1.1. This is likely an unintended consequence but a nice one nonetheless. Enjoy the unexpected update, Nexus 6 users!