As the name suggests, Android 7.1.2 is an incremental update that mostly focuses on “refinements, so it includes a number of bug fixes and optimizations,” according to the Android Developer Dashboard. The beta update is currently available to enrolled Pixel, Pixel XL, Nexus 5X, Nexus Player, and Pixel C devices. If you want to sign up for the beta, you can enroll here.
One of the silent features introduced in 7.1.2 is fingerprint gestures — a Pixel feature that seems to have made its way to the Nexus 5X. Nexus 5X owners are able to toggle fingerprint gestures on in Settings.
The update will also make its way to the Nexus 6P soon, which will likely introduce fingerprint gestures as well. The Nexus 6 and the Nexus 9 will not receive the update, as they are past the two-year support window and most likely will be the end of the road for them.
The Android 7.1.2 update will not come to the Nexus 6 and Nexus 9, as those devices have run their course of Android version updates. They will continue to receive Android security updates for another year.