Apple seeded macOS 10.12.1 Sierra Developer Beta 3 today, making build 16B2338c the third in less than two weeks. The last one was offered six days ago, and the first was six days before that. Interestingly, there still hasn"t been a second build of iOS 10.1, watchOS 3.1, or tvOS 10.0.1 in that timeframe.
macOS 10.12.1 is a minor update, so it doesn"t contain much in the way of new front-facing features. All that seems to be new is support for the iPhone 7 Plus"s Portrait Mode - which showed up in iOS 10.1 - in Photos. The release notes don"t say anything in the way of features or even known issues, which is fairly typical for a minor OS X/macOS release.
Today"s build is only available to developers at the moment, so if you"re on the Public Beta, you"ll probably see it tomorrow. Also coming tomorrow should be a third beta of Safari 10.0.1, which is the version of the browser that comes with macOS Sierra, but for OS X 10.10 Yosemite and 10.11 El Capitan.
To update to the new beta, head over to the Mac App Store and you"ll find it under the Updates tab.