Bridging the Semantic Gap: Leveraging LLMs for Hierarchical Interest Evolution in Sequential Recommendation

Abstract

Accurate user behavior modeling is fundamental to the prediction of click-through rates (CTR) in industrial recommendation systems and online advertising. Traditional discriminative models, which rely on isolated ID features, struggle to capture the evolving nature of user intents across multiple channels due to the inherent semantic gap. While Large Language Models (LLMs) offer rich semantic understanding to bridge this gap, their direct application faces two main challenges: modality misalignment between continuous semantic representations and discrete item IDs, and prohibitive computational costs that make them unsuitable for real-time inference. To address these issues, we propose the Hierarchical Semantic Interest Evolution Network (HSIEN), a novel generative-discriminative framework. HSIEN leverages an LLM to construct a Markovian state-space model that recursively captures and updates user interests from multi-channel behavior sequences. It then employs a Semantic Mixture-of-Experts (SMoE) strategy to aggregate multi-channel signals into hierarchical intent representations, which are encoded as compact dynamic semantic vectors for integration with downstream discriminative models. Extensive experiments on a public dataset and a large-scale industrial dataset demonstrate that HSIEN significantly alleviates modality misalignment and enhances CTR prediction performance through feature complementarity. This work provides a practical and efficient pathway for leveraging LLMs in large-scale recommendation scenarios.