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POS Tagging with Generative LLMs for Historical Germanic Low-Resource Languages: An Evaluation Against Fine-Tuned BERT

Part-of-Speech (POS) tagging is a fundamental task in Natural Language Processing, yet its performance on historical low-resource languages is still underexplored, particularly in the context of large generative models. While recent studies have demonstrated strong results for Large Language Models (LLMs) on modern languages and contemporary low-resource settings, their effectiveness for historical varieties remains unclear. Moreover, genre-specific structural variation, which may substantially affect tagging performance, has received limited attention. This study evaluates the zero- and few-shot POS tagging performance of two generative models on four historical Germanic low-resource languages across two literary genres. Their performance is benchmarked against fine-tuned BERT models. To contextualize the performance on historical data, the models are also evaluated on two modern languages. The results show that fine-tuned encoder models consistently outperform generative models across all settings. The performance of the LLMs on historical languages is substantially lower compared to that on modern languages, suggesting limited representation of these varieties in pretraining data. Furthermore, error analysis reveals structural output inconsistencies in LLM predictions that require additional post-processing. These findings highlight the limitations of zero- and few-shot generative models for historical low-resource POS tagging and underline the importance of task-specific fine-tuning.