In addition to releasing the first iOS 9.3.3 developer beta, Apple has issued OS X El Capitan 10.11.6 Developer Beta 1 through the Mac App Store. The first pre-release version is available to developer testers and features build number 15G7a (up from 15F34 on the public version).
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The latest OS X beta is relatively small at roughly 600MB but does require a restart to complete installation. Release notes appear outdated, however, as they specifically mention OS X 10.11.5, which Apple released to all users last week.
OS X 10.11.6 likely contains bug fixes, performance improvements, and security enhancements like the last few versions of the Mac operating system. User facing features at this point are likely being saved for OS X 10.12, which Apple is set to introduce next month at WWDC and likely launch later in the fall.
Features we’re expecting to see debut in the next major Mac update include Siri on the Mac (finally) and a new version of iTunes. OS X could also be renamed macOS or MacOS to fit the iOS/tvOS/watchOS names.