Yeah! The long wait is over! We are not going to mess around and will give you the blog post from the official Windows Blog:
“Today, we’re pleased to begin the roll-out of Windows 10 Mobile to select Windows Phone 8.1 devices. There are a lot of great new features in Windows 10 Mobile, like Continuum, Windows Hello and Cortana.
Consistent with our approach to the Windows 10 PC upgrade, we are focused on delivering a high quality experience for our customers. The Windows 10 Upgrade Advisor app can be downloaded from the Windows Store to see if the upgrade is available for your device.
You can see the current list of Windows Phone 8.1 devices that are supported for the upgrade to Windows 10 here.
This list includes a limited set of Windows Phone 8.1 devices and does not include some devices that are currently running Windows 10 Mobile in the Windows 10 Mobile Insider program. As Windows 10 delivers significant new innovations, many older devices are not able to successfully upgrade without an impact on the customer experience. Our goal is to only offer the Windows 10 upgrade to devices that we are confident can continue to deliver a good customer experience.
For more information on Windows 10 for phones, go here.
To download the Windows 10 Upgrade Advisor app, go here.
Updated March 17, 2016 9:23 am”