Earlier today, the update went live for Nexus devices across the board. You can now download Android 6.0 Marshmallow for the Nexus 5, Nexus 6, Nexus 7, Nexus 9, and Nexus Player.
As of today, the Marshmallow update is available for download directly from Google as factory images from their developer site.
Over-the-air (OTA) updates are not available yet, so if you'd like to perform the update directly on your device you may have to wait a little longer. Google hasn't mentioned when the OTA updates will roll out.
Marshmallow has several improvements, the biggest of which is battery life. Google reportedly managed to achieve a 30% boost in battery life for existing devices. There is a new feature in Marshmallow called Doze which aids longevity of the battery.
There are privacy improvements included in Marshmallow which will give users better control over what information an app can access. The other nice feature is Now on Tap which is Google's way of customizing content available to view for each user.
Google also announced two new smartphones last week - Nexus 6P and Nexus 5X. Both devices will ship with Marshmallow later this month. Those devices will have Google's Imprint technology, which is their native fingerprint authentication. Both devices include fingerprint sensors on the back.
Other smartphones will also get the Marshmallow update in the coming weeks. There are no timelines available at the moment. Those updates depend on individual manufacturers and carriers, the same way its been over the last few years. For those customers, it's a waiting game they are very familiar with.