The reproduction of Architeuthis is not well known. Hypotheses are based on observations of the sexual characteristics in dead Architeuthis and from the knowledge of other squid
Females produce enormous quantities of whitish to cream-colored eggs, about .5-1.4 mm long and .3-.7 mm wide, depending on the stage of their maturity. One female had over 5000 gm(over 11 pounds) of eggs in her ovary, well in excess of a million eggs. As in most oegopsids, females have a single median ovary in the posterior end of the mantle cavity, paired, convoluted oviducts along with mature eggs pass, then exit through the oviducal glands, and large nidamental glands that produce quantities of gelatinous material. Whether the eggs are laid into a large gelatinous matrix, as in most of the large oceanic squids or are released individually, is unknown, although the large nidamental glands suggest the former method.
Males tend to reach sexual maturity at a smaller size than do females. The two ventral arms are reported to be modified into transfering the spermatophores to the female. As in most other cephalopods, the single, posterior testis produces sperm that move into a complex system of glands that manufacture the spermatophores. These are stored in the elongate sac, or Needham's sac from which they are expelled during mating. The Needham's sac of fully mature males is packed with hundreds of spermatophores. Needham's sac terminates in the penis. The penis is so elongate that it extends anteriorly beyond the mantle opening. While mating has not been observed and the exact role of the penis is uncertain, some females have been found with spermatangia, the sperm-containing sacs of the spermatophore, embedded in the tissue around the bases of the arms and the head.
Cephalopods are known to be very fast growing animals. Some species of small, shallow water forms reach sexual maturity in 6-8 months, and most species about which growth, age and maturity data are available reach reproductive capacity within 12-18 months. Many of the specimens of Architeuthis that have been recovered have been mature, especially the females. But the age at maturity of Architeuthis is not known with certanity. One study suggests that adult size is attained within 3 years. Even at the rapid growth rate expected in cephalopods, the attainment of a mass of 500 kg or more in fewer than 3 years is impressive.