The Google Nexus 4 is receiving a new software update starting today which is being pushed OTA over-the-air. This is a very lightweight update at just 1.8MB in size which brings the JWR66Y (from the earlier JWR66V) software version with it.
Keep in mind that you will not receive this update if your device is rooted
T-Mobile has shared information regarding this update on their website and have stated that it is aimed to improve security on your device.. T-Mobile recommends that you have at least 50% battery on your device before you download and install the update.
The update is currently only available for the Nexus 4, but it is also expected to make its way to the other members of the Nexus family eventually.
source: T-Mobile | Android Central