Catalyzes three successive oxidations of the 4-methyl group of ent-kaurene giving kaurenoic acid, a key step in gibberellins (GAs) biosynthesis. GAs, which are involved many processes, including stem elongation, play a central role in plant development. ent-kaur-16-ene + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = ent-kaur-16-en-19-oate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] Plant hormone biosynthesis; gibberellin biosynthesis. Widely expressed. Highly expressed in influorescence tissues. In germinating seeds, it is mainly localized in the cortex and endodermis of embryo axis. Belongs to the cytochrome P450 family.