If you have a Pixel 2 or original Pixel and haven't noticed that Call Screening is working yet on your phone, it might be that it hasn't been activated yet. Even though the service doesn't require wi-fi, activation of it does, for unclear reasons (and I often keep wi-fi off, since I have unlimited data on T-Mobile, with great speeds at home). But even after I turned on wi-fi, it didn't seem to become available immediately -- I only noticed the "Activating" message go away after I went through the little tutorial (by tapping See a Demo).