The Windows Blue operating system update is likely to be named "Windows 8.1" when it hits later this summer, according to sources. From All About Microsoft:

The client version of Blue, codenamed Windows Blue, is a refresh of Windows 8. It is expected to be released to manufacturing around August of this year. As I've blogged a few times, Microsoft is planning to position Blue as part of the Windows 8 wave, not as Windows 9.

On Twitter this morning Roman L. (a k a @AngelWZR) tweeted a link to a screen shot, which I've embedded in this post, above, of what appears to be a build of Windows Blue that postdates the one that leaked a week ago. The week-ago leak was build 9364; the new one is 9375. It is labeled in AngelWZR's screen shot as "Windows 8.1 Pro." The original source of this screen shot is Winforum.eu.

 Microsoft's Windows Blue looks to be named Windows 8.1