The third beta of watchOS 3.1 has now been seeded to developers. We see this release one week after the second one. In this version we find some bug fixes and not much more. We haven’t found anything large like UI changes.
To get the latest build of watchOS 3.1, you can go to the Watch app and download it from there. If you don’t have watchOS 3.1 yet, you can download the profile from the developer center.