Microsoft has some bad news for those running Windows Phone 8.1 devices - the upgrade to Windows 10 Mobile won't be released in December after all. As such, the only way to try Microsoft's new OS this year (outside of the Windows Insider program) is to buy one of its two new handsets - the Lumia 950 or the Lumia 950 XL.

Gabe Aul, corporate vice president of the engineering systems team at Microsoft, recently announced the publishing of a cumulative update for Windows 10 Mobile Insider Preview Build 10586. In the post, Aul revealed that due to the holidays, the engineering team will be running at a slower pace and many of the key people who drive the process will be out (Aul included).

As such, they won't be releasing any new builds to Windows Insiders until January. That goes for both PC and mobile applications.

In a brief statement to ZDNet, a spokesperson for Microsoft said the Windows 10 Mobile upgrade will begin rolling out early next year to select existing Windows 8 and Windows 8.1 phones. The spokesperson didn't specify exactly which devices would or wouldn't be eligible for the update.

Microsoft officially unveiled its new flagship smartphones in early October after accidentally listing the devices on the Microsoft Store a week ahead of schedule. Both handsets went on sale in November.