In a statement, American said: “As part of a continuous evaluation of our network, American Airlines has made the difficult decision to discontinue service between Seattle (SEA) and London (LHR). We plan to operate 25 daily flights to LHR next summer from 10 destinations across the U.S.
https://onemileatatime.com/news/american-airlines-abandons-seattle-flights/
For those of us that had used Alaska FF miles to book nonstops to/from London this summer, this has a big impact. If you are in that situation, be sure to contact Alaska right away about award flight alternatives on British Air and Iceland Air.