In addition to iOS 9.2.1 beta 1, Apple has released OS X 10.11.3 developer beta 1 through the Mac App Store.
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The pre-release software doesn’t contain any release notes or focus areas, but likely includes further performance improvements and bug fixes. The first OS X 10.11.3 developer beta follows last week’s public release of OS X El Capitan 10.11.2 which had its own list of small fixes for the Mac operating system. The update is a roughly 650 MB download.