[nadams]

That's not what Google Fi support told me:

> Thank you for contacting Project Fi Support! My name is Sydney and I will be glad to assist with your issue regarding WiFi services today. First, your phone should connect automatically to open WiFi networks. They have to be Google verified networks to automatically connect. Here is an article regarding our feature known as WiFi assistant and how it works.

And I did try connecting to an open wifi - no VPN automatically activated (but that isn't the only thing that doesn't work...).

[mentat]

The assistant has to make the connection, not the user. I've seen it work against quite a few different APs including some obscure ones, so I'm not sure there's a list or not. The online docs suggest that it does some performance testing before connecting.

[redxdev]

By Google "verified", they seem to mean that the phone runs some tests on the network before actually connecting to the VPN, and disconnecting completely if the Wifi isn't up to par. It would be nice for them to confirm exactly how it works, though.

The VPN only works with access points that the phone automatically connects to through wifi assistant (this excludes any you have manually selected at any point in time). The VPN only works when the phone itself finds a hotspot that you have never selected and decides to connect.