Hyperbolic Prompt Learning for Incremental Event Detection with LLMs

Class-incremental event detection (CIED) is essential for real-world information extraction systems, which must continually recognize new event types without forgetting past knowledge. The main challenge lies in balancing stability and adaptability under data imbalance. Existing methods often underuse the hierarchical and syntactic structures of language, and thus limit the generalization capacity. We propose HPLLM, a hyperbolic prompt-enhanced large language model framework, motivated by the observation that both embedding distributions and dependency graphs in event datasets exhibit hyperbolic properties. HPLLM integrates two key components: (1) Hyperbolic LoRA fine-tuning, enabling geometry-aware parameter adaptation for hierarchical semantics; and (2) Hyperbolic Adaptive Graph Diffusion Convolution (HADC), which encodes syntactic dependencies into structure-aware prompts for LLMs. Together, these techniques strengthen semantic discrimination, reduce forgetting, and improve adaptation across incremental stages. Extensive experiments on ACE2005 and MAVEN demonstrate that HPLLM consistently surpasses state-of-the-art baselines in macro-F1, achieving stronger retention of old knowledge and better generalization to new event types. In particular, the model shows clear gains on rare categories with few training mentions, demonstrating its robustness in imbalanced and few-shot regimes.