After the official announcement of Android 5.1, Google has started to roll out the OTA updates for the Nexus family. The release is coming gradually to those devices, so if you don’t want to wait much longer, the factory images are already available for some models.
The first ones available were for the Nexus 5, Nexus 10, and Nexus 7 (2012). Surprisingly, the last flagship device from Google was not among them, but in a few days the file also been available for the Nexus 6.
Here you can find the download links for those devices. Before attempting to flash them, check that the building number match yours, or the update will fail. The update will bring all the devices to the number LMY47D.
Nexus 7 (2012) WiFi number LRX22G.
You probably know how it works. All those images can be found on the Google developer’s page, so you can check there the next days for the files that are not released yet.
Google has the detailed instruction to flash the images on the Nexus devices. All the steps are described on the same page, so read them carefully if this is the first time you attempt to install an update from an image file.
If you are interested in the binary files, there are some already posted (for the same models that the image files). There is no information yet regarding the other models, but they will probably be available soon.
Source: Droid-life.