Sources have said that the new update to Windows 8, also known as Windows Blue, will be called Windows 8.1. This is similar to the Windows Phone releases with WP7, WP7.1 and WP7.5 before jumping to Windows Phone 8. As Windows 8 is a new direction for Microsoft with more, but more incremental, updates it makes a lot of sense for these smaller version changes.
Microsoft executives like Windows Chief Financial Officer Tami Reller have said repeatedly that Microsoft envisions Windows 8 as something more than a one-season wonder. Reller has saidMicrosoft considers Windows 8 a product "of multiple selling seasons." So it makes sense that Blue would be christened Windows 8.x, not Windows 9.