Earlier today, AT&T announced that their Lumia 1520 is now receiving the Lumia Cyan and Windows Phone 8.1 updates. However, it quickly became evident that those with the Preview for Developers installed on their Lumia 1520s did not have an update, but those with Windows Phone 8.0 did. The reason for the discrepancy is Microsoft has put on hold updates for those running the Preview.
As such, those who are on the Preview and who still want the Lumia Cyan update need to downgrade their OS first. This is still Microsoft's position on the situation.