Apple has seeded watchOS 4.3 beta 2 to developers for testing following the release of iOS 11.3 beta 2. The build number is 15T5176c.
This beta version of watchOS 4.3 contains bug fixes and improvements.
For more information, visit: https://developer.apple.com/go/?id=watchos-4.3-sdk-rn
The software update also introduces support for Nightstand mode in portrait orientation.