The Windows Phone 8X was one of two devices (the second being the 8S) that HTC unveiled as its launch handsets for Windows Phone 8, way back in September 2012. The two phones were described as 'signature devices' for the OS - but neither of them will be getting an upgrade to Windows 10 Mobile.
In response to an enquiry from a Microsoft MVP on Twitter, asking if Windows 10 Mobile would make its way to the 8X, HTC's UK team delivered the bad news:
While that response does appear to leave the door open for a possible upgrade in the future, it's probably best not to get your hopes up. The first Windows 10 Mobile devices have already been released, and the rollout to existing handsets is now imminent. If HTC had any intentions of upgrading the 8X, it would already be 'planning' to do so at the very least.
As for the 8S, its measly 4GB of onboard storage fails to meet Microsoft's platform specifications for Windows 10 Mobile upgrades - existing devices require a minimum of 8GB to be able to upgrade.
Given that both the Windows Phone 8X and 8S are now well over three years old, it's not entirely surprising that HTC isn't planning to upgrade those devices to the newest version of the OS.
However, it's still not clear if HTC still intends to release any further Windows devices - despite the company's Chief Financial Officer saying last April that it was 'working closely' with Microsoft on a Windows 10 device, it hasn't revealed any further details on those plans.