Apple today seeded the second beta of an upcoming macOS Sierra 10.12.6 update to developers, two weeks after seeding the first 10.12.6 beta and a little over two weeks after introducing macOS Sierra 10.12.5, a minor bug fix update.
macOS Sierra 10.12.6 can be downloaded through the Apple Developer Center or through the Software Update mechanism in the Mac App Store.
No significant features or notable bug fixes were found in the first macOS Sierra 10.12.6 beta, and because Apple does not provide beta release notes, we may not know what’s included in the update until it sees a public release.
macOS Sierra 10.12.6 is likely to be one of the final updates to the Sierra operating system as Apple transitions to macOS 10.13, which will be introduced at the Worldwide Developers Conference in June.
Update: Apple has also seeded a second macOS Sierra 10.12.6 public beta for its public beta testers.