Gateways

I was told my old gateway cannot support 1000gigs and need to change to the new gateway. Do I need to change to the newer  gateway

Since we don't know what gateway model you have now, we can't say. But https://www.xfinity.com/support/articles/broadband-gateways-userguides lists all the gateways. The speeds they can handle are shown following the "Maximum data throughput" heading.

Note that "1000gigs" is not a speed Comcast/Xfinity offers. The max is 10 Gbps ("Gigabits per second").