Google has today uploaded Android Marshmallow factory images for the Nexus 6P, just as devices are starting to arrive for those who were part of the first batch of preorders. This isn't overwhelmingly exciting news considering the 6P ships with Marshmallow, but it's great that developers can now manually restore if something goes wrong while tinkering around.
Here they are, direct from Google's servers:
If you need help installing one of these, feel free to check out our guide to installing Marshmallow factory images.
Hilariously, Google's factory images site (at the time of this writing at least) has them listed as being for Android 5.1.1. Their build numbers clearly correlate with Android 6.0.0, though, so I'm going to assume this is a simple typo for now.