Capabilities and Evaluation Biases of Large Language Models in Classical Chinese Poetry Generation: A Case Study on Tang Poetry

Abstract: LLMs are increasingly applied to creative domains, yet their performance in classical Chinese poetry generation and evaluation remains poorly understood. We propose a three-step evaluation framework that combines computational metrics, LLM-as-a-judge assessment, and human expert validation. Using this framework, we evaluate six state-of-the-art LLMs across multiple dimensions of poetic quality, including themes, emotions, imagery, form, and style. Our analysis reveals systematic generation and evaluation biases: LLMs exhibit "echo chamber" effects when assessing creative quality, often converging on flawed standards that diverge from human judgments. These findings highlight both the potential and limitations of current capabilities of LLMs as proxy for literacy generation and the limited evaluation practices, thereby demonstrating the continued need of hybrid validation from both humans and models in culturally and technically complex creative tasks.