Arrived into Terminal G a bit over a week ago. At immigration there was a line next to the Mobile Passport line that was labeled as "EC" in a circle. Everyone in that line was holding a large laminated card with the EC logo and "Express Connection" on them (think similar to the ones they use for Pre-Check, but unlike the Pre ones they all looked brand new!). Based on details on a few of the boarding passes I was able to see them also holding, at least some of them were due to depart within the next hour.

I know that LAX has had this program for years for people with short connections, but I hadn't heard/seen it at SFO before last week. At least one of the immigration officers seemed confused by it, and kept asking why we were in two lines, and stating (to everyone and nobody at the same time) that we should all be in a single line - not sure if that's an indication that the MPC and EC lines were supposed to be a single line, or if he was just outright confused. Given there were 2 lines, the same immigration staff were basically just alternating between the two lines.