Not that Google officially announced the new Nexus 5X and Nexus 6P, their latest Android version can't be far away for current Nexus owners can it? Of course not! It's available today. The factory images for Android 6.0 Marshmallow for the various Nexus devices, including the Nexus 5, the Nexus 6, Nexus 9 and more are now online.
You can head over to the source link below and grab these factory image to flash on your device. It looks like it is only available to a select number of Nexus devices right now. Perhaps some of the excluded ones either need more time to bake or are simply too old to be compatible with Google's newest OS.
We aren't sure when the update will start pushing out OTA to the various Nexus devices, but it can't be long now. [Update: it looks like the update is already started rolling out OTA to several Nexus owners.]
Here's that source link: Factory Images for Nexus Devices