OTA update coming in the next week to existing Android Wear devices
Along with the new API for watch faces on Android Wear, Google today confirmed that Android 5.0 Lollipop is coming to your Android Wear smartwatch in the next week or so as part of the major updates announced today.
Over the next week, the latest release of Android Wear, based on Android 5.0 and implementing API 21, will roll out to users. All Android Wear devices will be updated to Android 5.0 via an over-the air (OTA) update. The update allows users to manage and configure watch faces in the Android Wear app on their phone, and install watch faces from Google Play. Any handheld device running Android 4.3 or later will continue to work with all Android Wear devices.
Google recommends that devs update their apps as soon as the Android 5.0 API 21 update hits watches — and not until then, because a watch face running API 21 won't be visible on a watch that hasn't been updated.
Google said it will "remove support for watch faces that don't use the official API in February 2015.
Source: Android Developers Blog