Apple has just proposed to the golden master version of OS X Yosemite. It is therefore of the final version, it is reserved for developers. The public will get it within the next week, Apple will announce the date at the next keynote.
Final versionThis version allows developers to test the final version of OS X Yosemite prior to public release. This is the final version that will be available on the Mac App Store and default in the new Mac. For information, the build number is 14A379a.
You may require a revision of the Golden Master is published prior to public release, this was the case with OS X Mavericks last year. But it was more of a problem than anything last minute thing. Point to note, it is possible to switch from OS X Yosemite Beta to OS X Yosemite Golden Master update is from the Mac App Store.
Interestingly, OS X Yosemite Golden Master is available with full conference that Microsoft will unveil the successor to Windows 8.