The second beta of macOS Sierra 10.12.3 has now been seeded to developers. We find this one week after the first release. We’re not sure what’s new in this version. According to the release notes, there are bug fixes and security improvements. However, we were not given anything specific.
To get the latest beta, developers can go to the Mac App Store and find it under the updates page. If you are not on the beta yet, you can go to the Apple Developer Center and download the installer from there.