Microsoft has just announced the new Windows 10 Mobile Redstone build 14291. This preview build is available for older Lumia devices, but is only distributed by the Windows Insider program.
The previously available version of Windows 10 Mobile was for devices that were released with Windows 10 Mobile already pre-installed, namely: Lumia 550, 650, 950, and 950 XL.
Build 14291 is the latest version of the Redstone update and can only be installed through the Windows Insider program.
Microsoft said that the Redstone build will be released to older Lumias after they receive the upgrade to Windows 10 Mobile, and given that the installation began last week, the company can now move forward with the upcoming OS update.
The only device that doesn't appear to be receiving the new Windows 10 Mobile Redstone build 14291 is the Lumia 635, but Microsoft says that this device will be supported at some point in the future.
Unfortunately, unsupported phones are not allowed to install the Redstone build, but they can continue to receive 10586.x updates, according to Microsoft's Gabe Aul. Devices like the Lumia 520 and 1020 are included in this list.
At the moment, no one knows whether the new devices will be supported at some point in the future.
