Apple has restarted its beta release cycle once again, one day after ending the previous cycle by shipping public releases, with new first beta builds of iOS 12.1, watchOS 5.1 and tvOS 12.1 being issued to developers for testing.
Developers enrolled into the testing program can acquire the new builds from the Apple Developer Center, or as over-the-air updates for devices using previous beta versions. Public beta versions usually ship within a few days of the developer betas, downloadable via the Apple Beta Software Program website, but typically arrive later for the initial builds.
The first iOS 12.1 developer beta is build number 16B5059d, while tvOS 12.1's first build is 16J5575c. The first developer beta for watchOS 5.1 is build 16R5559d.
It is unclear what each of the beta versions includes as changes or new features. AppleInsider is examining each release to determine what is new, and will report on the updates in the near future.
AppleInsider, and Apple itself, strongly advise against installing beta releases on mission-critical hardware, due to the potential for data loss. Those interested in testing the betas out should use secondary devices, and to keep backups of any important data before installing or performing updates.