Update: Microsoft clarified its blog post to reflect that only users with Windows 7 and Windows 8.1 can upgrade to Windows 10.

After a number of publications reported that Microsoft would be giving away Windows 10 for free to anyone as long as they test it out through the Windows Insiders program, Microsoft clarified its offer:

“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.”

In the original blog post, Microsoft made it seem like it would upgrade testers with the preview version to Windows 10. Gabe Aul, Microsoft’s general manager for the operating system group’s data and fundamentals team, wrote (emphasis ours):

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.

Only users with Windows version 7 and 8.1 will be able to upgrade to 10 for free — as long as they do so within a year of the release date.

Update on June 22: Microsoft updated its post again, this time with a full explanation. Below is the crux of it. Again, this is for Windows 10 testers.

If you want continue as a Windows Insider after July 29 (Windows 10’s launch date), there is nothing you need to do: “You’re already opted in and receiving builds in the Fast or Slow ring depending upon your selection. This is prerelease software and is activated with a prerelease key. Each individual build will expire after a time, but you’ll continue to receive new builds so by the time an older prerelease build expires you’ll have received a new one. Since we’re continuing the Windows Insider Program you’ll be able to continue receiving builds and those builds will continue to be activated under the terms of the Windows Insider Program. We provide ISOs for these builds for recovery from any significant problems, but they are still pre-release software. As part of the program we’ll upgrade Insiders to what is for all intents and purposes the same build as what other customers will get on 7/29, but that will be just another build for Insiders, and those who stay in the program will simply get the next build after as well.”

If you want to opt out of the Windows Insider Program and upgrade to the final copy of Windows 10 on July 29: “you will be subject to exactly the same terms and conditions that govern the offer that was extended to all Genuine Windows 7 and 8.1 customers. This is not a path to attain a license for Windows XP or Windows Vista systems. If your system upgraded from a Genuine Windows 7 or Windows 8.1 license it will remain activated, but if not, you will be required to roll back to your previous OS version or acquire a new Windows 10 license. If you do not roll back or acquire a new license the build will eventually expire.”

In other words, if you’re not a tester, you can’t get the final Windows 10 release on launch day by becoming a tester.