I have put the link below to the Forbes article on it. Apparently it will be free to any Windows 7 or 8 user for up to a year after it's release (if you want it you need to upgrade before July 29, 2016). I'm not a Windows user, but thought I would put this out there for any of you who are and haven't heard this yet.
http://www.forbes.com/sites/gordonkelly/2015/06/03/microsoft-windows-10-free-upgrades-upgraded/
http://www.forbes.com/sites/gordonkelly/2015/06/03/microsoft-windows-10-free-upgrades-upgraded/