American Airlines and JetBlue launched their ‘Northeast Alliance’ early in 2021. This means American and JetBlue,

• Are sharing some slots in New York, to let JetBlue expand its flying (American was underutilizing these)
  
• Codeshare on flights in and out of Boston and New York (you should almost never book codeshares if you can avoid it)
  
• Allow customers to earn miles and elite qualifying credit on each others’ flights

Until now there haven’t been elite benefits recognized between the two airlines, and there’s no redeeming miles for each others’ flights. Elite benefits, though, will begin soon. “Starting this fall” elite members of each airline will receive these benefits on the other carrier:

• priority check-in
  
• priority security
  
• priority boarding
  
• two complimentary checked bags

There’s no elite seating benefit at this point, but JetBlue’s elites only get extra legroom seats at the airport, if available.

The promise of this alliance is great for customers. It means more international flying for American, and more domestic flying for JetBlue. (There’s a fixed number of slots between the two carriers in New York, so these adds come at the expense of mostly squatted slots operated with small regional aircraft.)

JetBlue will split operations at New York LaGuardia between its current home in the Marine Air Terminal and new flights out of terminal B, eventually moving out of its old space. To facilitate the partnership across town, there’s a new airside connector bus at JFK going between American and JetBlue terminals.

The American-JetBlue alliance means that JetBlue and American together become players in the New York market against larger rivals United and Delta. Naturally competitors don’t like it (or use government review processes as a tool to extract a tax from the businesses).

However implementation of the partnership so far has been rocky at best. American can’t assign seats directly on JetBlue flights. American customers booking through Jetblue rather than American, trying to credit to AAdvantage, often have miles post to JetBlue’s TrueBlue program in error instead.

American elites booking codeshares get confirmations promising free bags already even though this isn’t yet a benefit. Fortunately this will change, and anyone getting such an email should seek reimbursement of their bag fees from American. (This is a DOT complaint waiting to happen.)

Update: An American spokesperson offers,

Thanks for the questions related to the customer experience in the Northeast Alliance. We understand there have been issues related to mileage accrual and seat selection on JetBlue flights and our team is working to resolve the technical challenges in the coming weeks.

Up next needs to be ironing out the kinks in the relationship, to get miles credited properly and seats assigned seamlessly. JetBlue needs to improve its elite seating benefit. And both carriers need to institute reciprocal mileage redemption.