When Microsoft started pushing out Redstone builds through the Windows 10 Mobile Insider Preview, it only came to Windows 10 Mobile devices, including Lumia 550, 650, 950, 950 XL, Alcatel OneTouch Fierce XL, and Xiaomi Mi4.
Gabe Aul had promised that once other devices were upgraded to Windows 10 Mobile, they would too be supported by the new Insider Preview builds. Today, he made good on that promise.
Here is the new list of supported devices for the Fast ring:
The firm also took the time to answer some questions that they thought would come up, such as what to expect if your device isn't on that list. The answer was that you have two options: roll back to Windows Phone 8.1 (if on the Insider Preview) or stay on the Insider Preview Release Preview ring until your device inevitably stops receiving updates sometime soon.
In short, if your device isn't on that list, don't expect to ever see it running Redstone. Sorry, Nokia Lumia Icon users.
Source: Microsoft Answers