According to notices on Apple's developer site, Apple has just issued a Golden Master build of OS X 10.9 to all registered developers today. Like the "release to manufacturing" builds in the Windows world, a GM build is usually the last stop on the way to public release. Apple has also issued a GM build of Xcode 5.0.1, which is necessary for building OS X 10.9 apps that will be submitted to the Mac App Store—Xcode 5.0 was released in September with iOS 7.

OS X 10.9 (also known as Mavericks) was announced alongside iOS 7 at Apple's Worldwide Developers Conference (WWDC) in June, and while it isn't the complete overhaul that iOS 7 is, it ushers in many improvements targeted specifically at power users. Among these features is a new tabbed version of the Finder that makes it easier to organize files and changes that make multiple-monitor setups more useful. New under-the-hood additions like compressed memory, timer coalescing, and "App Nap" should also reduce resource usage while increasing battery life.

Apple still hasn't announced pricing or availability details for Mavericks beyond the vague "this fall" promise it made at WWDC, but we'd expect the company to release the software before the end of October. The rumor mill expects Apple to hold an event in the middle of the month to announce refreshed iPads, and a Mavericks announcement would pair nicely with some new Haswell-equipped Retina MacBook Pros or perhaps the redesigned Mac Pro. Apple could also do what it did with Lion and Mountain Lion and announce Mavericks during its Q4 2013 earnings call, which ought to happen at some point before the end of October.

As we've previously reported, Mavericks is compatible with any Mac that can currently run OS X 10.8. We'll be publishing our usual in-depth reviews of both OS X 10.9 and its accompanying OS X Server update after Apple releases the software to the public.