It was the holiday train. Made stops at Stamford, Bridgeport and New Haven yards then returned to Harmon.
There was a 3-car train parked at GCT today around track 28 or so, consisting of 3 streamlined cars and a standard MNR diesel (a P32?). I couldn't tell if the platform was blocked off, but there was a pretty good-sized crowd there, with a lot of people wearing name tags, and checkout lane-type dividers set up on the platform.
Was this some type of Metro-North holiday event?