Apple's macOS Sierra has been on a slower tempo of preview releases than last year's El Capitan, hinting that the upgrade will launch in October.
Although Apple has been somewhat more transparent in its development process -- earlier this year it launched a new preview program for the Safari browser -- the Cupertino, Calif. company still does not publicly mark release dates on a calendar.
Clues to Apple's operating system launches are usually limited to comparisons with past practices, those then leavened with rumor and luck.
On Monday, Apple issued the sixth Sierra preview -- and the third this month -- to developers. Last year, Apple shipped the sixth beta of El Capitan on Aug. 3. Throughout July and August, each Sierra preview appeared between 10 and 15 days after the corresponding El Capitan beta of 2015. The average lag was 12 days.
If Apple follows a schedule similar to last year's -- when it released the El Capitan upgrade on September 30 -- Sierra's slower beta cadence signals a launch the week of October 9-15.
That would roughly match the release schedule of Yosemite, El Capitan's predecessor: Yosemite hit the Mac App Store on Oct. 16, 2014.
Coincidentally, the preview release tempo for Yosemite was more like this year's Sierra than last year's El Capitan. For example, Apple issued Yosemite's fifth preview Aug. 4, 2014 (Sierra's was Aug. 9), and the sixth on Aug. 18, 2014 (Sierra: Aug. 18).
macOS Sierra will be a free upgrade to all eligible Macs.