Update 1 for Windows Phone 8.1 became available for Developer Preview users on Monday. I should actually say, MOST users, because the Update seemed to be available for everyone except those with HTC device hardware. Microsoft stated they are working on the problem and that the issue has to do with specific OEM drivers that Update 1 needs to function correctly on HTC's smartphones. Today, HTC has issued a similar statement in its forums.
Translated from Chinese…
HTC after repeated communication Research Department and Microsoft, HTC Windows Phone 8X/8S upgrade 8.1 Update developer preview of items now make the following notifications:
HTC 8X will test your system stability push notification the first time after time, while HTC 8S because some hardware that does not meet the criteria, this will not be able to upgrade at is using HTC 8S friend can understand. More timely information will users please keep an eye on the official Micro-Blog messages, thank you for you continued support for HTC, thank you!
Based on the statement, it seems that HTC will definitely be working to ensure that the 8X devices are able to apply the update sometime in the near future, but unfortunately, those with 8S devices will be left out of Windows Phone 8.1 Update 1 testing – and quite possibly, will not be able to install the update at all outside the developer program when it becomes publicly available.
8S customers have posted responses to HTC's communication in the forums, and they're not happy. A specific date for the release of the 8X fix has not been promised.
Original link: HTC 8X/8S upgrade WP8.1 GDR1 preview announcement