I have to admit that I am pretty furious right now. I upgraded from Extreme 300 to Gigabit on July 4th. After the upgrade was applied to my account and I reset my modem, I was still getting the same Extreme 300 speeds as before, maybe a bit faster.
I looked into it, and the modem I had was the Cisco DPC3941T DOCSIS 3.0. This modem doesn't support Gigabit internet speeds. I got into contact with support to let them know this, and after a bit of a hassle (I already knew this modem wouldn't work) they sent me a new one. I was assured multiple times after several lines of questioning to Xfinity reps that I was being sent the XB6 DOCSIS 3.1 modem.
I looked into this modem previously and I knew that this was the one that my new service would require. However, the rep has zero knowledge of Xfinity equipment or services, and obviously is severely undertrained. He lied right through his teeth. I was on Friday that the ARRIS TG1682G had been added to my list of devices.
Bad sign, as from the modem thumbnail it looked identical to the Cisco DPC3941T that I already had. I looked it up on the manufacturer's website, and sure enough I was right. The ARRIS TG1682G is also a DOCSIS 3.0 modem and has a maximum throughput of 640Mbps. After getting it in the mail today, uninstalling my Cisco DPC3941T, and setting up the new ARRIS TG1682G, as expected I am getting the same exact "slightly-faster-than Extreme 300" speeds as before. It always caps out at around 470Mbps on both the Cisco DPC3941T and ARRIS TG1682G.
Neither of these modems are compatible with Gigabit internet service, and I already knew as much. When I saw that the Arris was added to my account on Friday I contacted support and was told not to worry, the XB6 is the modem that I was being sent.
This obviously was not true, the Arris showed up at my door just as I thought it would. I am making this post as a plea for help. I don't want to spend another several hours troubleshooting and talking to support to come to a conclusion that I already know. The Arris won't work with my service.
How do I get Xfinity to send me a modem that is compatible with my new Gigabit internet? If I contacted support again, I'm 99% certain that they'll just send me another XB3. Either another Cisco DPC3941T or ARRIS TG1682G.
Hope your issues get resolved as well. I made this post over on reddit's /r/Comcast_Xfinity/ subreddit. I think someone might get back to me sooner over there.
Since you're now being helped there, please continue to follow up with ccjohnf.
Locking this thread.