Xfinity is an ambiguous speed test. In other words, the results are often between values expected by mainstream speed tests and realistic speed tests.
The Xfinity speed test isn't recommended, due to the large standard deviation and the sometimes unrealistic high measurements.
With an advertised speed of 100 Mbps, the Xfinity speed test measured speeds between 84.7 and 128.8 Mbps. The deviations from the expected internet speed are that large that these results are unreliable. Besides that, the measurement of 128.8 Mbps is 15% above the true internet speed (in this case 112 Mbps) which is unrealistic high.
Xfinity was the number 2 speed test in the first speed test test of 2020. Due to the fact that Xfinity is an ambiguous speed test, it wasn't tested that often.
In the speed test overview you find all findings regarding the Xfinity speed test.