Apple on Thursday updated its beta macOS for the second time in a week, and has made the fourth beta of macOS Sierra available to developers for evaluation and testing.
The previous batch for all of Apple's platforms was provided to developers on Monday and shortly thereafter to the public.. The releases were made public shortly after the developer release.
It's not clear what changes are in the upcoming releases, though they are likely to focus solely on maintenance. Release notes from Apple mention "stability, compatibility and security" improvements, and no specific focus areas for testers.
The first two developer betas were released in December.