The article analyzes how English-medium instruction (EMI) programs in Russian universities transform students' academic success and academic identity under the influence of interrelated psycholinguistic and social factors. Theoretically, it is demonstrated that the transition to a non-native language of instruction generates a double cognitive load and shifts the determinants of success from subject preparedness to the ability to manage working memory, anxiety, and communicative behavior; at the same time, proficiency in professional discourse becomes not only a tool but also a condition for self-recognition as «one of us» in the academic community. Based on data from longitudinal observation in 2020-2023 involving 1845 students from four leading universities (compared with 600 students from Russian-language programs), supplemented by in-depth interviews, the nonlinearity of the relationship between English proficiency level and subjective states is revealed: groups with borderline levels B1–B2 exhibit a combination of heightened anxiety and heterogeneous adaptability, whereas high levels (C1–C2) are associated with increased engagement and self-efficacy but may also intensify pressures from expectations. Quantitative differences are systemic in nature: at B1, the average GPA in profile disciplines is 3.42 with anxiety 4.18 and engagement 42.65, whereas at C1 it is 4.67, 2.14 and 88.95 respectively; the proportion of students with high self-assessment of competence increases from 18,43% (B1) to 82,15% (C1). Social stratification is intensified by differences in initial educational capital: graduates of regional schools adapt on average in 8.35 months with stress 68.25 and dropout rates 14,85%, whereas graduates of international schools adapt in 1.15 months with stress 15.30 and dropout rates 1,02%. The dynamics of academic identity is described through growth in belongingness and autonomy in senior years alongside a reduction in the linguistic alienation coefficient from 0.78 to 0.28, with renewed deterioration upon entry into master's programs (0.54), interpreted as an effect of increased discourse complexity and heterogeneous student intake. The findings indicate risks of hidden segregation, the phenomenon of «academic silence», and the substitution of assessing depth of understanding with checking language competence, while also justifying the need for integrated language-subject support, propadeutic modules in academic literacy, and targeted tutoring for at-risk groups to prevent «natural selection» in internationalized education.