Apple has officially seeded the first developer beta for both macOS Sierra 10.12.1 and watchOS 3.1. macOS Sierra 10.12 was officially released to the public just yesterday, September 20, but watchOS 3 was officially released to the public last week. The new beta software is still new on the scene, so whatever tweaks and new additions Apple has added at this point still remains a mystery.
The new macOS Sierra developer beta is build 16B2327e.
The macOS Sierra 10.12.1 developer beta 1 is available as a download from Apple’s dedicated developer site. A public beta will probably be available soon.