If you are willing to move to Ubiquiti hardware (recommended, security breach from today notwithstanding) there's a relatively straightforward bypass method where the authentication packets are forwarded from the ONT to the AT&T box but it's otherwise out of the loop, and you have fully native routing with the Ubiquiti USG (a really nice router and ecosystem).
It's definitely not plug and play but I've been using this setup for a year and a half and I get my full 1gb bandwidth throughout my network with lots of hosts.
Instructions: https://medium.com/@mrtcve/at-t-gigabit-fiber-modem-bypass-u... Github project that makes it possible: https://github.com/jaysoffian/eap_proxy
It's definitely not plug and play but I've been using this setup for a year and a half and I get my full 1gb bandwidth throughout my network with lots of hosts.