Google just released Factory Images of the update for flashing to selected Nexus devices and they already begun pushing over-the-air (OTA) updates to them.
Get ready for the sweet taste of #AndroidMarshmallow. The update starts rolling out today. http://t.co/OGFhh3kkd0 pic.twitter.com/RSUpkI1MDt
— Android (@Android) October 5, 2015
These device will be getting the update : Nexus 5, Nexus 6, Nexus 7 (2013), Nexus 9, and Nexus Player will all receive the update to Android 6.0, build MRA58K.
Keep looking for those OTAs!