Nexus 4 with Android 4.3 appears, system dump available for the brave
Android 4.3 first made its appearance on the Google Play Editions of the Samsung Galaxy S4 and the HTC One, and now we see that the Nexus 4 too is a running a build of the new version. Jeff Williams, who purchased a Nexus 4 from a Google employee, much to his surprise, found that the purchased phone was running Android 4.3 JWR66N, coincidentally the same build running on the Play Edition of the Galaxy S4.
He has managed to upload the system dump of the phone, but there's no radio and bootloader in there. Jeff promised to upload them soon, and you can use TWRP to restore the dump. As always proceed with caution and a full backup.
If you wish to wait Google is going to announce the new version of Android on July 24 and will possibly start to seed the update the very same day. But if you are brave enough the system dump of 339 MB is available here or you can try the source link as well.