After rolling out the third beta a week ago, Apple has begun seeding testers with the fourth build of watchOS 4.3.1 for debugging on the Apple Watch.
To install the beta, navigate to the Watch app on your paired iPhone and tap the “My Watch” tab. From there, go to General > Software Update and you should see the build ready for download. Be sure to place your iPhone on Wi-Fi while downloading this software as it’ll surely gobble up plenty of your data.
So far, it looks like watchOS 4.3.1 will mainly contain bug fixes and security patches. Of course, we’ll let you know of any new user-facing changes made.