Upgrade Advisor app in working again on Windows Phone 8.1
Microsoft fixed the direct upgrade path to Windows 10 Mobile
No, Microsoft has not disabled the ability to upgrade from Windows Phone 8.1 to Windows 10 Mobile. The company has fixed the server-side issues preventing users with old Windows phones to get the official update to Windows 10 Mobile via the Upgrade Advisor app.
The app is again fully working and can be downloaded on any eligible for official update device running Windows Phone 8.1. When Microsoft released Windows 10 Mobile, the company did not roll out the update to all devices, but instead published an app for users willing to upgrade.
Although phones like the Lumia 1520, 930 and 830 can upgrade officially to Windows 10 Mobile using the app, they won’t be supported outside of the Anniversary Update branch. Microsoft announced last week that only 13 of the devices will be getting the Creators Update this spring, and can continue to receive Insider builds.
You can download the Upgrade Advisor app for Windows Phone 8.1 from the Store.