After Lumia Spain’s confirmation, Lumia US has also confirmed that Windows 10 Mobile will start rolling out in November to Windows Phone 8.1 devices. As you can see in the above screenshot, Lumia US Facebook account has revealed this info while replying to a question from a Lumia user.
Windows 10 Mobile brings lots of new features and UI changes over Windows Phone 8.1. You can go to our Windows 10 Mobile dedicated page to read all the changes and watch them in hands-on video demos, that Windows 10 Mobile brings with itself.