Google has just announced Android 7.1.2, a maintenance release focused on fixing bugs and improving performance. The initial devices eligible for the update are the Nexus 5X, Nexus Player, Pixel C, and both Pixel phone models. The Nexus 6P will be eligible, but not yet, with Google saying they expect the 7.1.2 beta will be "released soon."
Factory images don't yet appear to be live. Factory images are live here. Be sure to enroll your device in the beta program if you want to receive the OTA, which Google says will start rolling out soon.
As for what's changed? Google doesn't really say beyond a cryptic reference to "enhancements for carriers and users," whatever that means. We'll have to wait till we have it in our hands to know for sure.
- Android Developers