Windows 8.1 will be officially released in a month on October 18, 2013 (that's actually 12:00am on October 18th in New Zealand, so 4:00 a.m. PT 7:00 a.m. ET on October 17). Those who are already running Windows 8 will receive the upgrade to 8.1 for free, but those will on Windows 7 and below will need to pay for the pleasure to use the new Start Screen.
Pricing for Windows 8.1 will be the exact same as for the version before it: $119.99 and Windows 8.1 Pro will be available for $199.99. What's different from Windows 8, however, is that upgrade versions will be full version software.
"This shift allows more flexibility for customers in specific
technical scenarios and is in response to feedback we’ve received," Microsoft Brandon LeBlanc wrote. "It will be easier for those consumers who want to build PCs from scratch, run Windows 8.1 in Virtual Machine (VM) environments, or run Windows 8.1 on a second hard drive partition."
New PC owners with Windows 8.1 can upgrade to the Pro version for $99.
Those making the jump from Windows 7 can do an upgrade, but will have to reinstall desktop apps such as Office. Those upgrading from Windows XP and Vista will have to start clean as files, settings and programs will not transfer.
Furthermore, Microsoft recommends those upgrading from XP or Vista to purchase a retail boxed copy and perform a clean install.