Pre-trained language models, including large language models (LLMs), have become a general-purpose foundation for language understanding, reasoning, and generation. However, real-world use requires adaptation to specific users, domains, deployment con...
Pre-trained language models, including large language models (LLMs), have become a general-purpose foundation for language understanding, reasoning, and generation. However, real-world use requires adaptation to specific users, domains, deployment constraints, and trustworthiness risks. This study investigates domain-specific and trustworthy language model adaptation through four methodological approaches. The first approach explores user-aware adaptation by using LLMs as proxies for student groups with different ability levels. The second approach extends toward practical deployment by automatically generating annotated training data from structured menu databases and using store-specific adapters for scalable voice-ordering systems. The third approach addresses reasoning over professional documents by adapting an LLM to construction standards and classifying sentence-level overlap, conflict, and neutrality with selective reasoning. The fourth approach examines trustworthiness by measuring and mitigating media outlet name bias in LLMs, showing that contextual source cues can systematically affect model behavior. Overall, the thesis argues that reliable language model adaptation requires user modeling, domain grounding, deployment-aware specialization, reasoning support, and bias-sensitive evaluation.