Alongside Apple’s release of the OS X Yosemite Developer Preview Six, they also released a new beta version of their Xcode developer tools. However, after developers discovered the new version was unusable, Apple pulled it from their developer portal.
Apple has apparently fixed the issues affecting the beta, as it has been made available once again on the Apple developer site. The version number of the beta is two builds newer than the one seeded this morning.
The Xcode 6 Beta 6 is available for download at Apple’s Dev Center.