US vs. Chilean Passport Names

Asking here on behalf of a friend who just had a baby here in Chile (really, I am; lol):

He is American, she is Chilean (married). The Chilean birth certificate (obviously) has both of their last names. The kid’s Chilean passport will contain both last names, as is Chilean custom.

Question is: for the US passport application, is it required to show both names, or can it be dropped to just the father’s last name as is custom for the US?