A harder challenge is to win with 3 knights vs 1 knight, and that is more realistic as one may have to underpromote to a knight if the other side still has a knight on the board, to avoid getting forked:
If white promotes to anything else, then black forks the new piece on e6 resulting in a 2 knights vs lone king endgame which is a draw.
Decided to have some fun with a 250 ELO bot. I tried to keep as many pawns as possible and made bad moves on purpose in order to keep them. Eventually promoted them all to a Knight.