My assumption is that they are class 1, but its possible they are class 3.
You can search for other posts where people have gone into great detail on comparing their Sense reported numbers against the power company stats. Generally speaking, the consensus is that the Sense is within 1-2% of the electric company bills.
That 1-2% can easily be explained by a brief power outage, network connectivity issues, or the difference in time between what Sense considers Start and End of billing period, vs the power company. Or if there is still someone coming to read the meter by hand showing up at 10 am.
I am assuming Class 1 based on my own and other people’s observations of the perceived accuracy, in addition to assuming that Sense wants it to be accurate, but isn’t going to spend the money on a true revenue grade Class 0.x meter to save a little on the build price.
All that said, @kevin1 who has done a lot of digging into all of this may know more, or maybe JustinAtSense is able to give an official answer if possible.