Seems like they keep changing the interface to make it hard to find this. Must be my imagination.
1. Get logged in to your xfinity account and go to Manage Settings.
2. Click Internet.
3. Next to Public Hotspot, click Edit, then Disable.
I think it said something like “this can take 24 hours to process” and/or may have forced me to reboot my cable modem, I can’t remember. Anyway, this stops your cable modem from creating the “xfinitywifi” network. YES I REALIZE THAT THIS IS MEAN TO THE WORLD OR WHATEVER but I simply do not trust them not to send *me* to prison if some creep surfs kiddie porn from my driveway.