Apple on Thursday issued a developer's beta for watchOS 4.3, adding to the slew of Wednesday's test releases, though what exactly is in the update remains a mystery.
There are no notes associated with the watchOS beta. At present it is unknown what it contains, beyond bug fixes. Expected are the first moves towards AirPlay 2 compatibility.
The build number on the beta is 15T5165e. The way Apple's build numbers work for beta test releases as compared to the previous release lead to no easy comparison between the two to signify any magnitude of changes.