The update -- the sixth since El Capitan debuted last September -- signaled that its successor, macOS Sierra, may appear earlier on the calendar than the last several annual upgrades.
El Capitan 10.11.6 featured a very short list of resolved stability and compatibility issues, including unsaved parental control settings and inaccessible networked speakers and multi-function printers. A trio of enterprise-specific bug fixes were also baked into the update to improve startup time when connecting to a NetBoot server -- which allows Macs to be booted from a network, rather than the local drive -- and deal with a problem authenticating with Microsoft's Active Directory, a mainstay in corporations.
The update also patched 60 security vulnerabilities in more than a score of El Capitan's components, ranging from QuickTime and OpenSSL to graphics drivers and FaceTime.
El Capitan 10.11.6 may be the final non-security update to the current Mac operating system. For the last four cycles, Apple released just five non-security updates to each edition; not since 2009's Snow Leopard has Apple issued more than five.
More telling, Apple has a habit of capping the then-current edition about five to seven weeks before the successor goes public. Last year, for instance, Yosemite's final non-security update, 10.10.5, made the scene on Aug. 13, or 48 days before El Capitan's launch. In 2014, Mavericks last non-security update, 10.9.5, appeared on Sept. 17, 29 days before Yosemite's launch.
Under that schedule, macOS Sierra would land on the Mac App Store between Aug. 22 and the first week of September.
Because Apple updates the current edition of its desktop OS roughly every 8 weeks -- give or take a week or two -- there would be little chance of yet another El Capitan non-security update before Sierra unless Apple pegged the latter's launch for the end of October or early November.
That's unlikely.
An August launch of Sierra would not set a precedent: OS X 10.6, aka Snow Leopard, debuted Aug. 28, 2009. (And last year's El Capitan was released on Sept. 30, about two weeks earlier on the calendar than its Yosemite predecessor.)
Also today, Apple issued what was probably the final security update for OS X 10.9 Mavericks, patching 18 vulnerabilities in the three-year-old operating system.
Apple in June renamed its desktop operating system macOS, moving away from the OS X moniker it has used since 2000.
OS X 10.11.6 (El Capitan) can be downloaded from Apple's website, or from the Mac App Store and the operating system's built-in update service.