Microsoft will release the Windows 8.1 Preview version at the BUILD developer conference (June 26 - 28, 2013) but the company hasn't announced when the final version of Windows 8.1 will be released. Now a new rumor claims that Windows 8.1 could arrive in August, only one month after the public launch of the preview version, as there is no other beta build is in the pipeline for the time being.
In these 30 days, Microsoft will collect feedback and resolve potential issues found by Windows 8.1 Preview users.
Source: Paul Thurrott