Microsoft announced today on their Windows blog that Windows 8.1 “Blue” will be a free update for current Windows 8 users:
Today at the JP Morgan Technology, Media & Telecom Conference in Boston, Tami Reller shared with the audience that the update previously referred to as “Windows Blue” will be called Windows 8.1and will be a free update to Windows 8 for consumers through the Windows Store.
Unlike Service Packs for previous versions of Windows, Windows 8.1 introduces a lot of visual and functional changes. The public preview for Windows 8.1 will be available on June 26, with an RTM release scheduled at a later date.