The article reconstructs the logic of the transformation of authenticity in Simone de Beauvoir’s philosophy. It is shown that the early understanding of authenticity emerges from resolving the antinomy between the infinite regress of ends and the lure of immanent satisfaction. The solution is proposed through an ethics of ambiguity, where authenticity requires simultaneous recognition of freedom and facticity. At the next stage, authenticity is redefined as the subject’s capacity to resist social mechanisms that reduce a person to an object. The analysis examines how patriarchal structure blocks woman’s transcendence by imposing immanence upon her, and why liberation from this position cannot be reduced to mere imitation of male values. The study then turns to a shift toward existential anthropology: in Beauvoir’s later works, authenticity is linked to the acceptance of temporality, aging, and death as inescapable dimensions of facticity. It is concluded that the evolution of authenticity comprises three successive, yet not necessarily mutually exclusive, stages: from ontology to ethics, from ethics to social critique, from social critique to anthropology of finitude. Each stage incorporates the previous one into a broader context without abolishing it. Authenticity is thus understood not as a fixed state but as a process unfolding between freedom and situation. The relevance of Beauvoir’s thought for contemporary existential, gender, and age-related crises is substantiated.