Preview at WWDC likely in June, followed by September launch.
Apple Seeds Third macOS Sierra 10.12.1 Beta to Developers
macOS Sierra 10.12.1 beta 3 can be downloaded from the Apple Developer Center or through the Software update mechanism in the Mac App Store.
macOS Sierra 10.12.1 appears to focus on bug fixes and under-the-hood performance improvements to address issues that have been found since the operating system's release. Few outward-facing changes were discovered in the first two betas, but it does include Photos support for the new iPhone 7 Plus Portrait feature introduced with iOS 10.1. New features discovered in the third 10.12.1 beta will be listed below.
macOS Sierra is a significant update that brings features like Siri support, a new storage optimization option, cross device copy paste, auto unlocking with the Apple Watch, and more. For full details on macOS Sierra, make sure to check out our roundup.