Windows 10 will be free for beta testers, provided they keep testing
Microsoft has confirmed that users testing Windows 10 through the Windows Insider Program will be able to keep using the operating system for free, even if they didn't upgrade from Windows 7 or Windows 8.1.
If a tester wishes to keep using their preview copy of Windows 10, it will be upgraded to full the version on July 29. The user will however continue to receive prerelease software ahead of its public release, potentially exposing them to bugs. If a user opts out of this program, their copy of Windows 10 will eventually expire.
Alternatively, users who installed the Windows 10 beta on top of an existing Windows 7 or Windows 8.1 install will be able to opt out of the Windows Insider Program and continue to use the new operating system without testing newer updates.
Users who installed Windows 10 without upgrading will need roll back to Windows 7 or Windows 8.1 if they wish to opt out of the Insider Program and still receive the free upgrade.
Windows 7 and Windows 8.1 users not testing Windows 10 will be eligable for a free update when the operating system launches on July 29, provided they upgrade within its first year of availability.