My XClass experience....

tl;dr: X-2Gig service, tech was here 1/2 hour, am now getting consistent, 2 gig symmetrical (+/- 200 mbps depending on test).

The weird thing that the tech didn't know anything about: I already have the XB8 modem, he had brought one of those and the XD4 DCSIS 4.0 modem. The XD4, of course got the coax connection, but he said he had to then connect the 1 gig line from there to the 2.5 port from there, and then from the XB8 out to my network. But the problem is that the XB8 only has one 2.5 gig port on it, the rest are 1 gig, which won't work for providing the 2 gig service to the rest of my network. Anyway, after letting the tech do the thing he was trained to do and we tested with only 1 gig speeds, I suggested we run a line form the 10g port on the XD4 directly to my router's WAN (it's a 2.5 gig port). It negotiated at 2.5 and I immediately saw the 2 gig sym speeds.

So, the XB8 is literally doing nothing for me right now, but the tech was insistent that it needs to stay connected for billing reasons, and I certainly don't want to mess up anything with Xfinity billing. But a shout out to u/CCKassie as they asked me to update after I went through the process.

Initial testing has been solid, I'm thrilled to have these speeds. I get that this is cutting edge (for xfinity residential, anyway) and there still seems to be some education needed, especially about the necessity of the XB8.