ChatGPT is a large language model (LLM) that uses advanced natural language processing to understand and generate text and images. This entry examines the potential of ChatGPT (and similar LLMs) within the writing assessment context, highlighting its opportunities and challenges. It examines how ChatGPT can either support or complicate various stages of writing assessment, from test development to final evaluation. ChatGPT holds the potential to transform traditional product-based proficiency testing into a dynamic, process-oriented approach. A human-AI synergy approach is proposed, with humans acting as gatekeepers to harness this powerful yet fallible tool effectively and ChatGPT (or similar LLMs) serving as a digital extension of the human mind. Additionally, the development of AI literacy is advocated to address the ethical and practical challenges presented by AI integration in writing assessment settings.