Google Fiber utilizes VLAN packet tagging, for no really necessary reason. 
You’ll enjoy sharply curtailed throughput (even though the port is operating at 1Gb speed) unless your router supports it and you can figure out how to configure VLAN tag re-writing. DD-WRT seems to support it, but I never got it working. (If DD-WRT is so damn great, why does it seem like no-one shares their configuration recipes?) There are some tutorials online for configuring certain SO/HO switches to replace your Google Fiber router as gateway so you can get full speed. You’d connect that to the fiber jack and then you hang your gigabit-capable router of choice after it.
Placing a router, even a gigabit one, after the Google router results in a huge performance hit. But, I’d rather have my router manage my devices, so I settle for ~500Mbps and conceal my devices from Google behind a DD-WRT router which is configured to present a PC’s MAC on the WAN side so Google thinks it’s just a laptop. 
I only get ~700Mbps when my PC is directly connected to the Google router anyway so the difference isn’t noticeable. 500Mbps for $73.71/mo is still a good deal!
