Android 6.0 which is also known as Android M abbreviated as Android Marshmallow released the final SDK developer preview today. The new targeted API 23 applications are also started accepting via Google Play. After the preview of Android M in Google I/O and about the lots of feedback the final version of developer preview is released with new major added features.
Android Support Library is also updated to v23 along with the Android 6.0 SDK, which is focused on user permissions, fingerprint support, custom tabs, compatibility, power saving mode and much more. To update you can download the system images of Android emulator and developer preview to supported Nexus devices which helps in testing. The download is available from the developer preview site.
To run the app in the new Android Marshmallow with the older versions, Google Play provides the newly improved beta testing which helps all users to run the best of their app.