Tashkees-AI at AbjadMed 2026: Flat vs. Hierarchical Classification for Fine-Grained Arabic Medical QA

AbstractThis paper describes Tashkees-AI, a system developed for the AbjadMed 2026 Shared Task on Arabic Medical Question Classification. A comprehensive empirical study was conducted across 82 fine-grained categories, investigating three paradigms: fine-tuned encoder models, hierarchical classification, and ensemble methods. Leveraging a dataset of 27k Arabic medical question-answer pairs, an extensive ablation studies was conducted, comparing MARBERTv2, CAMeLBERT, two-stage hierarchical classifiers, and RAG-based approaches. The findings reveal that fine-tuned MARBERTv2 with data cleaning yields the best performance, achieving a macro F1-score of 0.3659 on the blind test set. In contrast, hierarchical methods surprisingly underperformed (0.332 F1) due to error propagation. The system ranked 26th on the official leaderboard.