The Nexus lineup from Google has always been ahead of the rest of the Android devices when it has come to getting the latest Android update. Google's two generations old flagships, the Nexus 4 and Nexus 7(2012) have just started getting the latest Android 5.1 Lollipop in India.
The Android 5.1 update is available as an OTA update. It has a size of 174.5MB for Nexus 4 and 101.6MB for Nexus 7. Google hasn’t released any official change-log for the update but has instead stated that it will improve the performance of the devices and brings bug fixes with it.
The update brings a revised Quick Settings menu in the notifications panel. It also comes with an enhanced ART (Android Run Time) which would allow for a faster opening of apps. The Android 5.1 Lollipop update for Nexus 5 had started rolling out earlier this month.
You will get a notification to install the same if your device is eligible to get it. Just in case you wish to manually check for the update, just head over to Settings, from there tap on About Phone and then on System Updates. Google has done pretty well to bring the latest software update to over two year old devices. Do let us know if and when you get the update.