Android 7.1.1 Nougat stable update is rolling out on Nexus 6P and Nexus 5X with Android 7.1.1 Beta. However, earlier on December 5th google has posted the stable build of Android 7.1.1.
The update weighs around 65 MB in size. It includes the Android security patch for the of December and running an even cleaner or more stable version of 7.1.1 than the last beta. Other than that, not much will be new since you were already running Android 7.1.1 in beta. Many Users of Nexus 6P and Nexus 5X have confirmed the Update.
As this is the OTA update if you did not receive the notification yet, Then don’t panic it will reach you by some time. Meanwhile you can check the update by going through the Settings of the phone.