New Windows 10 Mobile build 10586.122 is getting tested inside Microsoft
Windows 10 Mobile at one time was expected to roll out this coming Monday, which happens to be the earliest when we can expect this new build to be available. Instead, Microsoft now says that many Windows Phone 8.1 models are going to need a firmware update before they can be loaded with Windows 10 Mobile. And we still don't have a date when to expect Windows Phone 8.1 models to start receiving the update.
Previously, Microsoft said that certain models, like the Lumia 430, Lumia 532, Lumia 535, Lumia 540, Lumia 640, Lumia 640 XL, Lumia 735, Lumia 830 and Lumia 930 would get first crack at the Windows 10 Mobile update.
source: @tfwboredom via WMPoweruser, TechTimes