In various sources and also official ones from Intel, I get the number of max. 10.4 GT/s for the latest UPI interconnect, which connects for example Intel Xeon processors in the Skylake architecture. Now for the older Quick Path interconnects, I could find a lot of sources stating that with 2 bytes per transition and 6.4 GT/s, we get a bandwidth of 12.8 GB/s per link in one direction.
Now back to UPI: Is it still 2 bytes per transition, which means 20.8 GB/s per link per direction? I can not find any information about this on the internet except a German Wikipedia page here that is however annotated with the note that numbers might not be up to date.