Apple on Tuesday released a "golden master" of OS X Yosemite to developers, signaling that the upgrade is on track to ship within the next three weeks.
"Golden master," or GM, is a label some developers apply to software that is ready, or nearly ready, to ship or sell. Rival Microsoft has traditionally called the same milestone "release to manufacturing," or RTM, designating that the code is suitable for computer makers to install on new machines.
The appearance on the Apple developer website of Yosemite's golden master was reported Monday afternoon by several outlets, including MacRumors, and later confirmed by Computerworld.
Also on Tuesday, Apple issued a fourth public beta of Yosemite -- in the company's OS numerology, OS X 10.10 -- breaking with its almost-every-four-weeks cadence for the preview, another hint that Apple is wrapping up work on the upgrade. The third public beta build reached testers on Sept. 15, or just two weeks ago.
The developer build, available only to those who pay $99 annually, is labeled "14A379a," while the public beta, Apple's first since 2000, is pegged "14A379b." The two are essentially identical.
Yosemite's GM means that the release date is two to three weeks away. Last year, Apple issued the GM of OS X Mavericks on Oct. 3, then stocked the upgrade in the Mac App Store 19 days later. The lags between GM and launch for the two editions before that, Mountain Lion and Lion, were 16 and 19 days, respectively.
Those timelines bolster the expectation that Apple will debut Yosemite on Oct. 21.
Most Macs will be able to upgrade immediately: According to analytics vendor Net Applications, approximately 64% of all Macs ran Mavericks in September. (About 4% of all Macs already ran Yosemite last month.)
Both the golden master for registered developers and the latest public beta for others can be downloaded from the Mac App Store or by selecting "Software Update..." from the Apple menu on the top-of-screen menu bar.
Yosemite, like its forerunner Mavericks, will be free to download from the Mac App Store when Apple releases it.