Cosmos B plays in NPSL (current season and featuring 91 clubs).
There is no such thing as Cosmos A anymore. So Cosmos B is a reserve team for... what exactly, I'm not sure.
Cosmos A plays in NPSL Pro (starting in the fall and featuring 11 clubs).
Cosmos B features Danny Szetela, Santiago Castano and coached by Carlos Mendes.
Cosmos A will feature Danny Szetela, Santiago Castano and coached by Carlos Mendes.
The 'B' designation simply allows them to play in amateur leagues without tarnishing their 'professional' status and legacy.