Nokia says that all Windows Phone 8 powered Lumia models will receive Windows Phone 8.1
We wouldn't be surprised to see demand surge for low-end Lumia models over the next few days. The Nokia Lumia 520 is already the most popular Windows Phone handset. Also slated to receive the update, and Cortana, is the T-Mobile branded version of the Lumia 520 called the Nokia Lumia 521.
For those with a Windows Phone 8 powered handset, from the Nokia Lumia 520 to the Nokia Lumia 1520, summer can't get here soon enough. The update will be sent out OTA in a package called Lumia Cyan.
source: Nokia via Phonescoop