This model, entitled " AI CHATBOT-ASSISTED Cognitive Diagnostic Assesment in English Teaching and Learning" aims to provide a structured approach to implementing AI-driven tools within the framework of differentiated English language learning, specifically tailored to the Merdeka Curriculum at junior high schools. The Merdeka Curriculum emphasizes student-centered learning, fostering independence and creativity among learners. In this context, the need for innovative assessment methods that can adapt to individual learning styles and proficiency levels becomes paramount. This model proposes the use of AI chatbots as cognitive diagnostic assessment tools that not only evaluate students'''' language skills but also provide immediate, personalized feedback. By leveraging the capabilities of AI, educators can gain deeper insights into students'''' cognitive processes, allowing for more targeted interventions and support.