Apple today seeded the first beta of an upcoming OS X El Capitan update to developers



From MacRumors:

The new beta, build 15B17c, is available through the Software Update mechanism in the Mac App Store and through the Apple Developer Center. It is not clear what improvements the first update to OS X El Capitan will bring, but it's likely to include bug fixes and performance improvements for issues that have been encountered following the operating system's official release.

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