Hi,
Did some searching around but couldn't find any answers to this.

I am a Mosaic looking at a BOS-LAX flight later this year. The flight options using the new AA codeshare are significantly cheaper. However I notice that it gives me the message that no seat selection is available on the flight if I try to book one of these via jetblue.com.

1) Will I be able to upgrade to a Main Cabin Extra seat (this seems to be AA equivalent of EMS), either via cash or points? Will I even be able to select seats at all in advance?

2) Will any other Mosaic benefits be usable on an AA codeshare flight?

Thanks, appreciate the insight if anyone has had the chance to book any of these flights thus far. I am not enthusiastic about a transcon in regular economy with AA's 31" pitch, so I'm hoping that I can upgrade/select better seats.

Not yet. Besides AA, ts limited to those w. OW Sapphire & Emerald AND elite status on BA, AS, IB, LY or JL.

I'm a little confused. Are you planning to fly AA metal B6 codeshare or B6 metal on AA codeshare. AA metal on BOS-LAX disappeared for months. I would be very careful about booking AA metal this far out. Your flight would most likely be canceled.

AA metal, but booking via jetblue.com. Thanks for the tip. I'll hold off for now. They are showing $291 r/t price in late August which is less than half the cost of B6 flights.

Hopefully they will do a better job integrating their systems in the meantime. I never use AA so I'd prefer to stay within B6 for earning points.

Anything more than 30 days out is purely notional. That is true for both AA & B6, as well as other carriers. You can make a judgment about which carrier to use once things gel.

JetBlue has made it's summer cut already. Not final, but a lot closer than what aa has right now.