The public betas were essentially the same as the third developer previews that Apple released on Wednesday for iOS and OS X. Since the June 8 unveiling of the two operating systems, Apple has been updating registered developers -- who pay $99 annually for rights to access early-release code and tools -- about every two weeks.
Public beta testers won't get the same builds as developers, nor on that frequent a cadence. If Apple moves this year as it did last with OS X Yosemite -- the first public beta of the Mac OS since 2000 -- it will refresh public participants' code about once a month, or every two developer builds.
But not everything is the same as 2014: Not only has Apple added iOS to the beta pool, it's kicked off the program three weeks' earlier than last year.
In 2014, Apple launched the Yosemite public preview on July 24, or seven weeks and three days after the OS's unveiling at the firm's annual developers conference. This year, iOS 9 and El Capitan went public four weeks and three days after WWDC's announcement.
Apple has not revealed release dates for the final builds of either iOS 9 or OS X El Capitan, but if it follows precedent, it will start serving up the former in mid-September and the latter four weeks later. It's unclear if the earlier-than-last-year launch of the El Capitan public beta means that the upgrade will also debut sooner on the calendar than in 2014, or if Apple released OS X 10.11 today simply because it was also sending iOS 9 to testers. iOS 9's time-for-public-testing will be about the same as Apple had last year for Yosemite.
Participants in the iOS 9 and El Capitan betas will be able to install the finals in place of the previews when the polished versions launch this fall.
As it did last year, Apple again warned testers not to spill any beans. "Don't blog, post screen shots, tweet, or publicly post information about the public beta software, and don't discuss the public beta software with or demonstrate it to others who are not in the Apple Beta Software Program," Apple told potential testers in a FAQ. The full terms of the beta program were also posted on Apple's website (download PDF).
The same warning last year was widely ignored.
iOS and OS X owners interested in living dangerously can register with the beta program here, then enroll their devices in one or both programs to receive the preview and follow-on updates.
Apple urged beta partakers to back up their devices before installing the previews, and included links to instructions for reverting back to the stable iOS 8 and OS X Yosemite in its FAQ.