According to Mary Jo Foley, the target date for Microsoft’s Windows 8.1 Update 1 is March 11.
If Microsoft does hit the March 11 date with Windows 8.1 Update 1, that release will hit just a few weeks before the Windows Phone 8.1 operating system supposedly will. Rumors have indicated that Windows Phone 8.1 (a k a “Blue”) will RTM just prior to the kick off of Microsoft’s Build 2014 conference, which starts April 2.
Foley, M. J. (2014). Microsoft’s Windows 8.1 Update 1: Rumored release target is March 11. ZDNet. Retrieved January 24, 2014, from http://www.zdnet.com/microsofts-windows-8-1-update-1-rumored-release-target-is-march-11-7000025559/.