Not every device has Marshmallow (Android 6.0) because it was recently released by Google and apart from that, even lesser devices have the Marshmallow 6.0.1. The above image is of the Cherry Mobile Android G1 (H220) which is one of the Android One devices which have received Android 6.0.1 (Marshmallow).
As I said 2 days ago. Android 6.0.1 become available for Android One program… pic.twitter.com/ap8NL4lImE
— LlabTooFeR (@LlabTooFeR) November 20, 2015
Also, if you see the “Android security patch level,” you’ll find that it’s dated December 1 which is yet to come. Seeing it, we could assume Google has already finalized the Marshmallow 6.0.1 update but the changelog hasn’t been out yet which means that we don’t know what this update brings with it.
PhoneArena has also reported that according to this HTC ROM developer, LlabTooFeR, Google is going to release the Marshmallow 6.1 next year.