Michail Bakhtin’s philosophy of act is considered as a metaphysical project. Bakhtin’s conception is explored in a wider context of the metaphysical project of Russian existentialism. Interpretations of the term “truth”, which correspond to different versions of existentialism, are compared. Shestov’s existentialist particularism, Berdiaev’s actualistic personalism, Bakhtin’s ethical existentialism are analysed. Existentialist implications of Gregory Palama’s metaphysics of light are considered.