The Android M Developer Preview is here, and you'll be able to have it on your Nexus soon.
If you have a Nexus 5, 6, 9 or Player, you'll be able to download and flash an Android M Developer Preview in short order, and while it's focused on developers to get acquainted with the new version, we're sure a few enthusiasts will be taking a peek as well.
Google says that the Android M Developer Preview images will be updated "often" based on developer feedback. For now, you can download the latest factory images right here.
More: Google Developers