This isn't new - United has eticketing agreements with airlines they aren't in an alliance with. You can book AS or DL legs on 016 stock.
You won't get any benefits or mileage earnings for the non-UA legs.
AS will interline baggage with UA according to their Baggage Interline Agreements.
Last edited by JALsnipe; May 16, 2022 at 10:41 am
Reason: removed incorrect info