Following the Nokia Lumia 1320, its higher-spec brother the Lumia 1520 too is receiving its Lumia Cyan update. Microsoft has also just updated their availability list with a total of 4 Lumia models currently up to date with the latest Windows Phone 8.1.
If you haven’t received any notification yet on your Lumia 1520, you can check manually under Settings > Phone update.
Thanks @Steady2Twit for the alert!