<p>English-medium instruction (EMI) has expanded rapidly in transnational higher education and has become an important site of second and foreign language learning in disciplinary contexts. Yet how EAP–EMI integration is related to students’ academic language experience and perceived academic success as an institutional learning condition remains underexplored. This study investigates the relationships among perceived EAP–EMI integration, academic language-related challenges, EMI-related self-efficacy, and perceived EMI academic success in a Sino–US transnational higher education programme. Survey data were collected from 405 undergraduate students with sustained EMI exposure and analysed using structural equation modelling. Results indicate that perceived EAP–EMI integration is strongly associated with lower academic language-related challenges and higher perceived EMI academic success. Academic language-related challenges function as an important experience-near mechanism linking institutional alignment to students’ evaluative outcomes. EMI-related self-efficacy is closely calibrated to experienced challenge and operates in a differentiated manner, indicating both facilitative and constraining associations with perceived academic success once institutional alignment and experienced challenge are taken into account. Overall, the findings support a process-oriented account of academic language learning in EMI contexts, highlighting how perceived academic success emerges from the interplay among institutional alignment, language-mediated academic experience, and students’ evaluative beliefs in second and foreign language education settings. Future research could extend this work through longitudinal, multi-site, and performance-based designs to examine more robustly how these relationships develop across different EMI contexts and stages of study.</p>