I along with several other Canadians I know with the Nexus 6P, we are seeing Google’s Wi-Fi Assistant appear as an option on our devices. For me, it took a power cycle to have it show up.
Wi-Fi is a service from Google, and they explain it as;
To stay connected in places where your cell connection isn’t as strong, you can have your phone or tablet automatically connect to open Wi-Fi networks that we’ve verified as fast and reliable. Wi-Fi Assistant is a free service that makes these connections for you securely.
This is unfortunately not available to everyone. Wi-Fi Assistant is available only for Nexus devices running Android Marshmallow (5.1) and up, and only in some countries, including Canada.