After a hiatus of almost three weeks after the second, Apple has just made available to developers the third beta of the iOS 12.1.3 (compilation 16D5037a) of watchOS 5.1.3 (16S5535a) and the tvOS 12.1.2 (16K5534a). MacOS Mojave 10.14.3 has been left out of this lead, at least for now.
For now, nothing very relevant has been discovered in these updates and the version numbers themselves even indicate that these are updates to make bug fixes and general enhancements.
Precisely for this reason, we can expect all of them to be released in January. At most, I would say, they should win one more beta build after today.
Update 01/07/2019 at 16:30
New trial versions of iOS 12.1.3 and tvOS 12.1.2 have also been made available to Apple Beta Software Program members.
Update II 1/7/2019 6:08 PM
It took a few hours, but now it's also gone to developers macOS Mojave 10.14.3 beta 3 (compilation 18D38a). Soon, an equivalent test version of him should also paint on the Apple Beta Software Program.