Doing a dummy booking for November, you can click through and pay for your seats as part of the overall purchase, so you’re not committed.

It it seems to be $111 per leg in this case though this may vary between seats and/or change over time.

It’s also worth mentioning that buying the flight with a hotel could save $1k or so on a 10-day trip and that you might want to wait for the flights to fill up before committing to seat selection (though these are both very full routes).

Finally, you’ll be only one AA domestic first away from BA silver status (OneWorld Emerald) after this trip.