Google has announced a new "enhanced network" for Project Fi, their MVNO service that will soon be rebranded. The feature promises to add extra security and more reliable connectivity. They are accomplishing this with an always-on VPN.
Project Fi actually already uses a VPN. That's how it switches between the 3 networks it uses while you're out and about. The new "enhanced network" mode will extend this to include WiFi networks that aren't included in Project Fi.
When you enable our enhanced network, all of your mobile and Wi-Fi traffic will be encrypted and securely sent through our virtual private network (VPN) on every network you connect to, so you’ll have the peace of mind of knowing that others can’t see your online activity.
Another cool feature of the "enhanced network" is the ability to automatically switch between WiFi and mobile networks. Similar to how it works with the 3 Project Fi networks while you're away from home, Fi can switch between WiFi and cellular when the connection isn't fast enough. This will be handy when you're on the edge of a WiFi network and the signal is weak. Normally, your phone would cling to the WiFi connection until it's completely gone.
Google made sure to clarify that your traffic is not tied to your Google account or phone number in any way. The "enhanced network" feature is available only for Android Pie devices and is in beta right now. You can activate it inside the Project Fi mobile app once it arrives.