It appears that KS had taken over by the time I flew out of BOS for Memorial Day weekend. AS is still in terminal A, at the same gates as before (near the Harpoon brewery).

When I was checking my bag, it looked like several employees were undergoing training. I bet the AS agent that the OP interacted with was an AS employee on temporary assignment in BOS to train the KS agents.

Other small changes:

The ticket counter has moved to the far end. If my sense of direction is accurate - it's the east end. There were still some old AS kiosks (with the screens/computers removed) by their old ticket counter, but it appears that DL as reclaimed the counter space.

When I returned to BOS, the baggage carousel that AS used was to the left, after exiting the secure area (instead of to the right where it had always been before).