When Microsoft released the Windows 10 Mobile upgrade for older devices last March, it didn't exactly inform users that it was available. Instead, you had to be aware of it, and go to the Store to download the Upgrade Advisor app, which would then determine if your handset was eligible for the update.
While Upgrade Advisor remains available through the Store, Microsoft seems to have shut down the service, breaking the one official upgrade path that existed. Naturally, you can still use the Windows Insider app to upgrade through the Insider Program. Once you do, you can set your phone to the Production ring.
The news comes after the firm announced yesterday that just 13 devices will be eligible for the Windows 10 Mobile Creators Update, effectively ending support for all Windows Phone 8.1 devices aside from the Microsoft Lumia 640 and 640 XL. Once again, if you have a phone that was dropped from support, you can continue to receive updates via the Release Preview ring of the Windows Insider Program.
We tested out Upgrade Advisor on a Lumia Icon, 1520, and 640, and none of them worked, despite the fact that the 640 is still an officially supported device. And Microsoft hasn't updated any of the factory images that are available through the Windows Device Recovery Tool, so if you use the app to reset your phone, you'll be back on Windows Phone 8.1 without a proper upgrade path.
If you have a Windows Phone 8.1 handset and you're still considering installing Windows 10 Mobile, now would be the time to do it. While using Windows Insider might be OK as a workaround for now, that won't last forever.
Thanks to Michael West for the tip!