Yes, it’s free – for fully licensed valid installs of Win7 / Win8.1
If you have a pirate copy, you will have to pay. The good news, for folks that register for the upgrade – future updates will also be free. Good move Microsoft.
Windows 10 is coming July 29th 2015
Windows 10 will see the illustrious return of the Start menu — except it isn’t quite the Start menu that you’re used to from Windows 7. In fact, it’s better! The Windows 10 Start menu is possible the best Start menu yet.
The left side of the Windows 10 Start menu is, except for some new coloring and formatting, is mostly identical to Windows 7. There are a few improvements, however: The power button has moved to the top, and the right-hand menus like Documents, Computer, and Control Panel have moved to the left, to a “pinned” section at the top. This frees up the right side of the Windows 10 Start menu for… live tiles.