I have been reading some of this news articles comments various sites, some still don't believe it will be a legal licensed version if you upgrade from insider preview to windows 10 rtm. They are still thinking you have to a key or a previous version. At least we know better.
Here is another tweet from Gabriel.
Surprised they're doing it like this. I was thinking MS would either say "lol format" or instead give a free upgrade to Final (home) for Insiders that have been registered for 3 months or more, and Pro for those over 6 months. And sent a pandabear to those that registered in October 2014
Awesome they finally clarified this, was beginning to wonder if I needed to another 7 build or not.
Real simple If you do a clean install of build 10130, sign up for a Microsoft Account . Once upgraded to the release. You will be able to activate without any previous license and it will be genuine. Then you can download the release iso for a later clean install that will be pre-activated.