I flew SEA-EWR on Sunday and sat next to several AS employees and they mentioned the move (I'm more invested in AA now than DL, so actually prefer this location). The odd thing is I couldn't recall what day they said the move would happen and so on Tuesday I called customer service at AS to find out if my flight would be departing out of A. To my surprise, they had no notice of the impending change! Very quickly and stealthily done!