This study aims to analyze the implementation of authentic assessment within the Merdeka Curriculum in Islamic Religious Education (PAI) and Character Education at Al Anwar Junior High School and Al Anwar Senior High School, Sarang, Rembang. The study employed a qualitative approach with a multisite case study design. Data were collected through observation, semi-structured interviews, and documentation involving school principals, curriculum coordinators, PAI and Character Education teachers, and students. Data analysis followed the interactive model of data condensation, data display, and conclusion drawing and verification, while data credibility was strengthened through source and technique triangulation and member checking. The findings indicate that authentic assessment has been implemented as an integral component of learning rather than merely as a mechanism for determining final grades. Teachers employ various assessment techniques according to learning objectives and material characteristics, covering students’ knowledge, skills, attitudes, and participation. A notable finding is the difference in assessment complexity across educational levels. At the junior high school level, authentic assessment emphasizes conceptual understanding, attitude habituation, and simple application in daily life, whereas at the senior high school level, it involves greater independence, higher-order thinking, problem solving, presentation, and contextual application of knowledge. Assessment results are also utilized to provide feedback and determine instructional follow-up. The study concludes that the quality of authentic assessment is determined not primarily by the diversity of instruments but by the coherence between learning objectives, assessment activities, evidence of achievement, feedback, and follow-up. The study contributes a cross-level perspective on authentic assessment in Islamic educational settings by identifying a gradation of assessment complexity according to students’ developmental characteristics.