Update (6/22): Microsoft has had to clarify their stance on the Windows Insider program, and it seems this last time they've finally figured it out. To learn exactly how it's going to go, read our updated feature:

Is Windows 10 Free? Yes, and No. An Explainer

Update (6/21): Is Microsoft backtracking? Maybe, maybe not. After a tech media frenzy on Saturday, because, well, free Windows is an unseen phenomenon, Microsoft quietly updated their original blog post with this: "It’s important to note that only people running Genuine Windows 7 or Windows 8.1 can upgrade to Windows 10 as part of the free upgrade offer."

Some believe this goes back to the same story from last March, when similar ambiguity lead media to believe Windows 10 was going to be given away. Microsoft is not getting rid of the ambiguity in full this time either, and the blog post has comments closed so users can't ask for clarification. Others, like long-time Windows reporter Ed Bott, believe this is all in purpose.

His theory is that the original/edited blog post won't mention the Windows license status because it would get Microsoft in a compromising legal situation. Windows is not free, not to PC builders, OEMs, or enterprises. But "with a wink and a nod" they are telling us that for individuals, here's one way you can get it, and ultimately they want you to drive adoption. We'll be keeping an eye on any further developments.

The original story follows below:

Microsoft has finally committed to something I suspect they intended to do all along (or not? see below). Windows 10 Insiders (anyone who is currently using the Windows 10 Preview builds) will receive a direct upgrade to the final release of the operating system and that copy will remain valid indefinitely. Even if you decide to clean install later, you get your free copy of Windows 10. Thanks, Microsoft.

The only requirement is that as part of the Insider program, your Preview build needs to be connected to a Microsoft account, and then the final copy of Windows 10 will be associated to this account. There will be one or two additional Preview builds before the OS goes RTM and launches July 29, so it's likely signing with the MSA (Microsoft Account) will be made mandatory in one of those builds, as hinted in the company's official blog post:

Windows Insiders running the Windows 10 Insider Preview (Home and Pro editions) with their registered MSA connected to their PC will receive the final release build of Windows 10 starting on July 29th. This will come as just another flight. I've gotten a lot of questions from Windows Insiders about how this will work if they clean installed from ISO. As long as you are running an Insider Preview build and connected with the MSA you used to register, you will receive the Windows 10 final release build and remain activated. Once you have successfully installed this build and activated, you will also be able to clean install on that PC from final media if you want to start over fresh.

It's crystal clear Microsoft is serious about moving as many people as possible to its latest platform and as soon as possible, even if that means giving it away. At this year's Build conference, the company forecasted 1 billion devices would be running Windows 10 in three years and that becomes easier to accomplish now that the offer is not limited to valid Windows 7 and Windows 8/8.1 users.

The Windows Insider Program will also continue after Windows 10 is launched. Insiders will keep receiving future updates, there will be a fast and slow ring, and according to Redmond they will begin to work on the next release of Windows immediately after Windows 10 ships. Also note that Windows Enterprise edition customers are excluded from the free offer since they need to activate using the Volume Licensing Service Center.