It is widely known that Google Nexus owners are the first to receive any new Android updates and it remains true for Android 6.0 Marshmallow. Here are the Android 6.0 Marshmallow OTA links for Nexus 9, Nexus 9 LTE and Nexus 7 LTE.
Android 6.0 MRA58K from 5.1.1 LMY48T
Android 6.0 MRA58K from 5.1.1 LMY48T
Android 6.0 MRA58K from 5.1.1 LMY48P
While Google is known for taking its sweet time to rollout OTA updates, those who are impatient can download these updates from Google servers and manually update their device.