Apple is now on its third round of developer betas, with new builds of iOS 13.3.1, iPadOS 13.3.1, watchOS 6.1.2, and tvOS 13.3.1 now available for testing.
The latest builds can be acquired by developers in the beta-testing scheme via the Apple Developer Center, or as an over-the-air update for hardware already using earlier beta builds. A public beta version of the releases is expected to start arriving soon, and will be available through the Apple Beta Software Program website.
The first batch of builds were released on December 17, while the second followed after a break for the holidays on January 14. The previous beta cycle, for iOS 13.3, iPadOS 13.3, watchOS 6.1.1, and tvOS 13.3, ended on December 10 after four rounds.
As release notes for each of the betas advise there are "no release notes" available, it is unknown exactly what the updates will consist of, other than expected bug fixes and performance improvements. The incremental naming of each operating system strongly lends itself to these being maintenance releases, rather than updates with larger feature changes.
Both AppleInsider and Apple strongly suggest users avoid installing betas on to "mission-critical" or primary devices, due to the potential for data loss or other issues. Instead, the recommendation is to install betas onto secondary or non-essential devices, and to ensure there are sufficient backups of important data before making any major changes.
Update: Public betas have also been released.