1.2Gbps plan with 1000Mbps speed

As a Gold member, I was suggested to upgrade my Internet plan from 800Mbps to 1.2Gbps (bundle with Mobile) in December 2022. Unfortunately, after receiving and installing the Xfinity XB7 modem, my Internet speed went up to 950Mbps. After hours spent with numerous Xfinity Ambassadors (wish Ambassador should have more power) and switching to an XB8 modem, the Internet speed did not increase. Finally, an Xfinity technician was sent (I guess Ambassadors are very busy and do not do visitation). The technician did run multiple tests and discovered that the speed on the Coax cable (before the modem) was 1.6Gbps while the speed directly after the modem was 950Mbps – precisely the same speed I was receiving! He suspected that the modem might cause the issue with low speed. He suggested switching the modems; unfortunately, he had just XB7 readily available. After activation of the new modem, the internet speed remained the same – 950-960Mbps (never more than 1000Mbps). Interestingly, the Xfinity gateway (http://10.0.0.1/) showed the Internet connection speed on all four LAN Ethernet ports as 1000Mbps. A few days ago, I had another conversation with Xfinity Ambassador, who did run multiple tests but found no issues. Again, I received a similar suggestion to change the modem back to XB8; the Ambassador promised that this step will solve all issues with my Internet speed. I received and activated the new modem, and … appears that the last Ambassador was laying (shame on you!) … no change in the Internet speed, and the Xfinity gateway shows the same connection speed (1000Mbps).

I’m using Intel(R) Ethernet 10G 2P X550-t Adapter on my main computer; the Internet speed is the same on all laptops; I’m wondering does Xfinity placed an incorrect connection speed limit (up to 1000Mbps instead of 1.2Gbps) on my account, or the modem is causing the issue. Should I get my own ARRIS Surfboard G36 to receive the internet speed I was promised?