We’ve known for a while that when Windows 10 comes out, it will be a free upgrade to most users. What if you’re using the preview version, though? Yep, you’re included. So if you’re on an old version of Windows that isn’t eligible for the upgrade (like XP or Vista), installing the Preview can get you in the door.
As Microsoft details on its Windows blog, if you’re running the Windows 10 Technical Preview as part of the Windows Insider Program, and you have a valid Microsoft account connected to your installation, you’ll be upgraded to Windows 10 for free. If you’re already in the program, future builds will prompt you to connect your Microsoft account if you haven’t already done so.
While this is good news for those on the preview builds, it’s also a handy workaround for anyone who might be getting left behind when the free upgrades start rolling out. Microsoft is only extending the free upgrade path to Windows 7 users and higher, so if you’re running XP or Vista, you’d need to pay for the full version in order to get Windows 10. However, if you install the Preview now, you’ll be included in the free upgrade path. This also works if you’re building a new PC now.
Upcoming changes to Windows 10 Insider Preview builds | Windows Blog