Any model which finds its origin in no less than fundamentals i.e. abstract in thought may be regarded as ab-intio. In this context both quantum and classical theories are based on fundamental approaches viz. the Schrodinger equation and the Newtons equation which do not have more fundamental underlying concepts are ab-intio models.
classical electrodynamics is also based on fundamental natural concept of charge and interaction between charges and hence can be considered as an ab-intio theory. The fundamental equations may be the Maxwell’s equations governing the electromagnetic laws.