The relevance of the research topic is due to interest in the phenomenon of Russian cosmism, which, on the one hand, is actualized with a new stage of space exploration, on the other hand, requires philosophical understanding against the background of the spread of “noospheric thinking”, both in its scientific and natural format, and in its religious-philosophical and gnostic-esoteric. Such close attention to the phenomenon of Russian cosmism is associated with the tendency to search for the origins of the concepts of trans- and posthumanism in the philosophy and scientific ideas of Russian cosmists – mystics, scientists, artists and philosophers. In particular, their search is due to the anticipation of the views of transhumanists – in the ideas of immortalism, the “improvement” of man, the “fusion” of man and the cosmos, overcoming physicality in the works of Russian cosmists. The purpose of the study is to identify the origins of transhumanism and posthumanism as concepts in their essential connection with the ideas of the philosophy of cosmism. The scientific novelty of the study lies in the confirmation of the thesis of discursivity, in its “vertical dimension” as metaphysically saturated and characteristic of Russian cosmism, but not such for trans- and posthumanism, with their “horizontal”, postmodern dimension. As a result, it has been proved that the fundamental question underlying the differences between cosmism, trans- and posthumanism is hidden in the depth of the essential ontological and existential foundations of human existence. The authors consider the existential basis of death to be the basic existential basis, which is clearly traced in immortalism as immanently inherent in both cosmism and trans- and posthumanism. The practical significance of the study lies in the disclosure of the specifics of Russian cosmism, its role and significance in philosophical thinking, the establishment of a correlation between the ideas of cosmist philosophers and modern transhumanist projects. The theoretical basis of the study, along with the works of Russian scientists, philosophers (both thinkers of the late XIX – early XX centuries, and modern ones), were publications and works of foreign authors, which consider the provisions on the origins of modern trans- and posthumanism in Russian cosmism, as well as philosophical concepts of the posthuman (Manzocco R., 2017; Braidotti R., 2021; Ferrando, F., 2021; Elchaninoff M., 2022 et al.). The study of the topic of the origins of trans- and posthumanism, in our opinion, is productive precisely in the aspect of the philosophy of Russian cosmism, as evidenced, for example, by modern works of authors – Suslov A.V. (2021), Yudina B.G. (2018), Elchaninoff M. (2022) and others.