Just a day after Apple released iOS 11.3 developer beta 2 the company rolled out watchOS 4.3 beta 2 for Apple Watch. watchOS betas are available only to developers, and needs an iPhone that’s also running iOS developer beta.
watchOS 4.3 beta 2 includes iPhone music controls, Nightstand Mode portrait orientation, and improved AirPlay controls.
You’ll need an active Apple Developer account to participate in the Apple Watch betas. You can sign up at Apple’s Developer website.