Hypoxia is associated with increased erythropoietin (EPO) release to drive erythropoiesis. However, a prolonged sojourn at high altitude results in an increase in EPO levels followed by a decrease, although erythropoiesis remains elevated at a stable level. The role of hypoxia and related EPO adjustments are not fully understood and contributed to the formulation of the theory of neocytolysis. In this study, we aimed to exclusively evaluate the role of oxygen on erythropoiesis comparing in vitro erythroid differentiation performed at atmospheric oxygen, with a lower oxygen concentration (3% O2) and with cultures of erythroid precursors isolated from peripheral blood after a 19-day sojourn at high altitude (3450 m). Results highlight an accelerated erythroid maturation at low oxygen and more concave morphology of reticulocytes. No differences in deformability were observed in the formed reticulocytes in the tested conditions. Moreover, hematopoietic stem and progenitor cells isolated from blood affected by hypoxia at high altitude did not result in a different erythroid development, suggesting no retention of high altitude signature but rather an immediate adaptation to oxygen concentration. This adaptation was observed during in vitro erythropoiesis at 3% oxygen, displaying a significantly increased glycolytic metabolic profile. These hypoxia-induced effects on in vitro erythropoiesis fail to provide an intrinsic explanation to the concept of neocytolysis.