The Android Wear 2.0 development train keeps on rolling with the release today of a new developer preview build. The biggest change in the new build is the addition of new APIs for authenticating on your phone for a watch-based app. As Google explains in today's blog post:

To make authentication a seamless experience for both Android phone and iPhone users, we have created new APIs for OAuth and added support for one-click Google Sign-in. With the OAuth API for Android Wear, users can tap a button on the watch that opens an authentication screen on the phone. Your watch app can then authenticate with your server side APIs directly. With Google Sign-In, it's even easier. All the user needs to do is select which account they want to authenticate with and they are done.

Other changes include support for on-watch billing for in-app purchases, through a four-digit Google account PIN. There are also new cross-device promotion APIs for allowing developers to push users to a relevant phone app on the Play Store. And the swipe-to-dismiss gesture, removed in the earlier previews, is back in today's builds. Support for "legacy apps" using the older Wear 1.0 app delivery mechanism has also been added. And it's now possible to peek to actions at the bottom of items without scrolling through the entire list.

The fact that major user-facing changes are still being made shows that Wear 2.0 remains in flux even at this late stage in its development. The new builds are available for the Huawei Watch and LG Watch Urbane 2nd Edition LTE. We're still due a fifth Android Wear 2.0 developer preview build before the new version is finalized early in 2017.