We have been using it with Xfinity and we experience 100mb/s through our existing -separate - wireless router (60mb/s in the worst spot in the house).
We were recommended to use a new modem with the DOCSIS 3.1 technology but it does not offer any faster speed or better latency from what we observe and we could have stayed with that Motorola DOCSIS 3.0 for a much longer time, oh well...
If you are renting a modem from Xfinity, this is your chance to get rid of a small payment, they add up :)