The router used in AT&T fiber can vary depending on the specific package or plan. However, some of the best routers that are compatible with AT&T fiber include the TP-Link Archer AX21, TP-Link Archer AX73, ASUS ROG Rapture WiFi 6 AX, NETGEAR Orbi RBK852, and the Synology RT2600ac. These routers offer budget-friendly options, high performance, gaming capabilities, mesh networking, and good security features. It's important to check with AT&T or your service provider to see which routers are recommended for use with their fiber internet service.