Statement of the problem. The music theater of Ph. Glass is an important part of both the work of the composer himself and the musical culture of the 20th – 21st centuries, which is confirmed by the constant interest of researchers. However, it has been discovered unevenly, and the late operas of Ph. Glass remain almost unlit, which does not provide an opportunity to follow evolution of this genre. Objectives, methods, and novelty of the research. The purpose of the study is to reveal the specifics of the genre metamorphosis of the opera in Ph. Glass’s music theater based on the analysis of three operas – “Einstein on the Beach” (1976), “Akhnaten” (1984), “The Perfect American” (2013) – and to determine the trajectory of the evolution of the composer’s musical theater. The scientific novelty of the research lies in the fact that for the first time it is proposed to consider the evolution of Ph. Glass’s musical theater as a movement towards tradition; parallels with the musical genre in the opera “The Perfect American” are revealed for the first time, and the features of the baroque opera in “Akhnaten” are clarified. The structural-functional method, genre-stylistic analysis, comparative analysis are used in the study. Research results and conclusion. The analysis of three operas by Ph. Glass illustrates the movement towards tradition. In “Einstein on the Beach” (1976), which was not originally conceived as an opera, the features of this genre appeared on a significant scale, preserving the verbal component (parts of readers), vocal (chorus) and stage (pantomime, choreography, scenery), while there is no traditional linear plot, fixed text libretto and characters – bearers of solo vocal parts. “Akhnaten” includes a number of operatic components absent in “Einstein”, in particular, a linear plot, written text libretto, characters with solo vocal parts, a chorus part with a verbal text, an expanded orchestral composition, traditional operatic forms (arias, duets, trios, choirs, ballet scene). Other features, such as the choice of the plot, the use of the countertenor, the role of wind instruments (trumpet), and the use of chaconne, show the reference to baroque model of opera. In “The Perfect American” the connection with tradition brings closer the work to the American “mainstream” due to the reliance on the genre of the musical. This is reflected in the two-act structure with the disproportion like in a musical, in the pairing of events and scenes, the role of duets, the system of reprises, as well as the approach of choral melodies to popular songwriting. As a result of the analysis, it is concluded that, having started his journey in the field of music theater with the radically innovative “Einstein”, Ph. Glass made a crooked evolutionary loop, first delving into the past (baroque opera), then returning to the present and approaching the border of academic and popular music (musical).