Google WiFi will work with DHCP, Static IP or PPPoE ISP connections.
AT&T is typically one of the three, depending on your service area and type of connection. Be sure you have all your AT&T account information available before installing. You will be required to enter a username and password with a PPPoE connection, otherwise choose DHCP and let Google WiFi do the rest. (unless you have a static IP assignment from AT&T, then you can enter that in the setup wizard)