HTC released the HTC 8X about 3 years ago. The device received Windows Phone 8.1 a while ago, and if you are waiting for Windows 10 Mobile, you will be disappointed: the company isn’t planning to release any further updates for the 8X.
@StefanMalter There are no further updates planned for the HTC Windows phone 8X currently ^CD
— HTC UK (@HTC_UK) January 11, 2016
Of course, not a lot of HTC’s customers use the 8X anymore and the device is also quite old now. Windows 10 Mobile is yet to roll out to old Lumia devices, and some other devices from third-party OEMs. It isn’t yet known if HTC will be releasing Windows 10 Mobile for the HTC One M8, but it will be quite surprising if the OS doesn’t come to the company’s latest and greatest Windows Phone.