Android Wear 2.0 preview 4 adds sign-in, in-app billing, more
Android Wear 2.0 developer preview 4 adds a certain number of new APIs that will allow developers to create better standalone apps for smartwatches.
Thanks to the newly added Google Sign-In, authentication should be simpler than ever, as users will only need to select which account they want to authenticate with.
Another important new features added in this build is in-app billing support, which allows users to authorize purchases faster and much easier via a 4-digit Google Account PIN.
Furthermore, a couple of Android Wear 1.0 feature make a comeback in this preview build per users request. For example, activities now automatically support swipe-to-dismiss gesture.
Also, there's new fragment and view support, as well as a hardware button that can be used as a “power” button instead of “back,” which means it can no longer be intercepted by apps.
source: Google
Things that are NOT allowed: