If you have Windows 8 licence then Windows 9 will be a free for you, according to a translated article on Indonesian site Detik.com. The website published a statement by President of Microsoft Indonesia, Andreas Diantoro confirming the news. Diantoro siad, "when the OS (Windows 9) was launched later, users who have been using Windows 8 just need to do the update via his device. It will be installed automatically."
ZDNet also reported a few months ago that Microsoft was thinking about making the next version of Windows free for Windows 7, 8 and 8.1 owners.
Source: WPCentral