SETRec++: Scaling Order-agnostic Identifier for Large Language Model-based Generative Recommendation

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Leveraging Large Language Models (LLMs) for generative recommendation has attracted significant research interest, where item tokenization is a critical step. It involves assigning item identifiers for LLMs to encode user history and generate the next item. Existing approaches leverage either token-sequence identifiers, representing items as discrete token sequences, or single-token identifiers, using ID or semantic embeddings. Token-sequence identifiers face issues such as the local optima problem in beam search and low generation efficiency due to step-by-step generation. In contrast, single-token identifiers fail to capture rich semantics or encode Collaborative Filtering (CF) information, resulting in suboptimal performance. To address these issues, we propose three fundamental principles for item identifier design: 1) integrating both CF and semantic information to fully capture multi-dimensional item information, 2) designing order-agnostic identifiers without token dependency, mitigating the local optima issue and achieving simultaneous generation for generation efficiency, and 3) disentangling semantics across different tokens, unlocking the potential of scaling order-agnostic identifier. Accordingly, we introduce a novel set identifier paradigm, representing each item as a set of order-agnostic tokens. To implement, we propose SETRec, which leverages CF and semantic tokenizers to obtain order-agnostic multi-dimensional tokens. To eliminate token dependency, SETRec uses a sparse attention mask for user history encoding and a query-guided generation mechanism for simultaneous token generation. We instantiate SETRec on T5 and Qwen (from 1.5B to 7B). To reinforce disentanglement between tokens, we propose SETRec++, which introduces two disentanglement strategies, i.e., disentangled regularization loss and token masking mechanism. Experiments on four datasets demonstrate its effectiveness across various scenarios ( e.g., full ranking, warm- and cold-start ranking, and various item popularity groups). Moreover, results validate SETRec’s superior efficiency and scalability on cold-start items as model sizes increase, and SETRec++’s potential in the scalability of order-agnostic identifier.