Implicit Reasoning for Large Language Model-based Generative Recommendation

Researchers at arXiv propose PauseRec, a lightweight implicit reasoning paradigm for large language model-based generative recommendation, which outperforms explicit chain-of-thought methods by up to 6.22% while reducing training costs by 65% and inference speed by 71.3%.

arXiv:2606.14142v1 Announce Type: new Abstract: Large Language Models LLMs are increasingly adopted as backbones for Generative Recommendation GR , promising access to pretrained world knowledge. Yet reliably invoking this knowledge for GR remains poorly understood. A key obstacle is that LLM-based GR typically represents items with Semantic IDs SIDs , disrupting LLMs' natural-language reasoning interface because these tokens are unseen by the LLM during pretraining. Existing approaches address this with expensive multi-stage pipelines that ground SIDs and elicit explicit rationales, but offer limited insight into when and why each stage is necessary. In this work, we systematically decompose explicit reasoning training pipelines for LLM-based GR, revealing three key limitations: weakened world-knowledge verbalization, misalignment between SID and natural-language token embedding spaces, and sensitivity to rationale quality, all of which hurt explicit reasoning performance. To circumvent these issues, we propose PauseRec, a lightweight implicit reasoning paradigm tailored for GR. PauseRec is exceptionally practical, avoiding costly reasoning trace acquisition and reasoning alignment training, leading to a multitude of benefits: 1 it outperforms standard explicit CoT methods by up to 6.22%, 2 it reduces training cost by up to 65% GPU hours, and 3 it speeds up inference by up to 71.3%. These results position PauseRec as a lightweight alternative to explicit rationale generation, enabling more effective and efficient LLM-based GR.