Microsoft recently acknowledged that the much-anticipated Windows 10 Mobile update will be rolled out to a slew of Windows Phone OS-powered smartphones. Nevertheless, a definitive time frame for the update was not given by the tech giant.

Now, it looks like about 50 percent of the active Windows Phone handsets will not be receiving the Windows 10 Mobile update “anytime soon,” according to AdDuplex Founder and CEO Alan Mendelevich.

As it turns out, AdDuplex took into account the “number of active users” pertaining to each Windows Phone handset to arrive at the 50 percent figure. However, Microsoft initially noted that the company would try and update all the possible Windows Phone handsets to the latest Windows 10 Mobile OS. But, going by AdDuplex analysis, about 50 percent of Windows Phone handsets that are active right now will not be updated anytime soon.

Microsoft apparently took this decision based on the feedback from the device owners using the company’s Insider Builds. The tech giant will only roll out the update to those handsets where the firmware build receives “most positive reviews.”

While AdDuplex CEO said 50 percent will not receive the update “anytime soon,” MSPowerUser says those handsets may “never receive” the latest firmware. In any case, readers should note that Microsoft has not confirmed this report yet.

AdDuplex shows the Nokia Lumia 520 is the most used Lumia variant with a whopping 12.9 percent share out of all Windows Phones. The Microsoft Lumia 535 takes the second place with 11.7 percent share. adduplex-jan2016-devices-global Chart showing all the Windows Phone devices that are active across the globe. Photo: MSPowerUser, AdDuplex

Meanwhile, here is the list of eligible handsets earmarked to receive Windows 10 Mobile update: Nokia Lumia 1520, Nokia Lumia 930, Microsoft 640, Microsoft Lumia 640 XL, Nokia Lumia 730, Nokia Lumia 735, Nokia Lumia 830, Microsoft Lumia 532, Microsoft Lumia 535, Microsoft Lumia 540, Nokia Lumia 635 1GB, Nokia Lumia 636 1GB, Nokia Lumia 638 1GB, Microsoft Lumia 430, Microsoft Lumia 435, BLU Win HD w510u, BLU Win HD LTE x150q and MCJ Madosma Q501.

However, the widely-used Nokia Lumia 920 and Nokia Lumia 520 will apparently not be receiving the new firmware at all, Phone Arena reported.

Here is the official tweet from CEO of AdDuplex: