American Airlines announced a new “strategic partnership” including codesharing on some routes in July 2020. In January 2021, several other enhancements to this partnership were announced, including:

”Important components of the alliance will be introduced starting in the first quarter of 2021 and phased in over the course of the year:

• Seamless customer experience
  With each element of the alliance, customers flying in and out of New York and Boston will enjoy a more seamless experience across both airlines, including the ability to book a single itinerary on either website, access to the alliance’s significant global network, convenient connections, access to loyalty benefits and an improved on-the-ground experience — resulting in a compelling proposition for both leisure and corporate customers.
  
• Network alignment in the Northeast
  The alliance will offer customers the largest network in New York City and Boston, and it will enable new strategic growth opportunities for both airlines, accelerate the replacement of small regional jets with larger aircraft, while greatly expanding the connectivity between each carrier’s network in the Northeast. American will upgauge aircraft and by the end of 2021 will operate all service out of New York with first class. Starting in the first half of 2021, JetBlue and American schedules in New York and Boston will begin to be aligned to give customers new flight options, with improved schedules, better connections, competitive fares and access to more domestic and international destinations.
  
• Expanded service in the Northeast
  As part of the alliance, JetBlue plans to significantly expand its service at New York LaGuardia Airport (LGA), as well as further expand in other NYC airports and in Boston. The alliance will also allow JetBlue to reactivate aircraft that would otherwise sit idle. An expanded operation at LaGuardia further advances JetBlue’s position as New York’s Hometown Airline® and accelerates the airline’s ability to recover.
  
  As previously announced, American is introducing brand new service on from New York (JFK) to Tel Aviv (TLV) and Athens (ATH). American’s loyal customers in New York will be introduced to their first long-haul international service in more than four years, with even more new routes on the way.
  
• Codeshare agreement
  Starting later this quarter, JetBlue will place its B6 code on a variety of American flights in New York and Boston. Likewise, American will place its AA code on select JetBlue flights also in at New York’s John F. Kennedy International, LaGuardia (LGA) and Newark Liberty International (EWR) airports, as well as Boston Logan International Airport (BOS). Flights touching New York or Boston from either JetBlue, American or connecting combinations of both will be bookable on jetblue.com and aa.com in the coming weeks. The codeshare will introduce JetBlue customers to more than 60 new routes operated by American and will introduce American’s customers to more than 130 new routes operated by JetBlue.
  
• Reciprocal loyalty benefits
  Later this year, customers of both JetBlue’s TrueBlue and American’s AAdvantage® programs will be able to enjoy reciprocal benefits, including the ability to earn and/or redeem points or miles on either carrier making both loyalty program even more valuable. The airlines are also exploring opportunities to recognize JetBlue Mosaic customers and American’s AAdvantage elite members across both airlines. More details will be announced to loyalty program members later this year.“

Link to January 12, 2021, AA news release

As of Jan 31st, 2022 - Benefits typically do not show up when managing the booking and will show up when checking in online.

To receive elite benefits add your AAdvantage number at time of purchase, or contact JetBlue customer service to add it after purchase.

JetBlue Basic: AA elites still get free seat selection and a free bag on Blue Basic fares. All passengers are allowed to bring on board a personal item that fits under the seat. However you do not get to bring a free full size carry-on with Blue Basic except when you select an Even More Space seat.

AA Loyalty Points can take a week to post.

AA Link to Benefits page