Microsoft’s new Lumias 950 and 950 XL packed with Windows 10 will ship in November but existing Windows Phone users will have to wait for a Windows 10 until December. Microsoft said broad availability for Windows 10 on mobile phones will start by the end of the year.

To be eligible for the Windows 10 upgrade your phone must be rocking the Lumia Denim update (version 8.10.14219.341, or higher) and have 8GB of internal memory available.

Of those Denim Lumia phones, the ones slated to get Windows 10 Mobile first include the Lumia 430, Lumia 435, Lumia 532, Lumia 535, Lumia 540, Lumia 635 (1 GB RAM), Lumia 640, Lumia 640 XL, Lumia 735, Lumia 830, and Lumia 930.