LLM-Powered Relevance Assessment for Pinterest Search

Pinterest Search presents a methodology for scaling search relevance assessment using fine-tuned LLMs to replace costly human annotation.

• •A cross-encoder architecture fine-tunes open-source multilingual LLMs (XLM-RoBERTa-large selected for balance of quality/speed) on a 5-level relevance scale using human-annotated data
• •Pin representation combines titles, descriptions, BLIP image captions, board titles, and engaged query tokens as textual features
• •Stratified query sampling design replaces simple random sampling, using a query-to-interest model and popularity segments to define strata
• •LLM labeling reduced Minimum Detectable Effects (MDE) from 1.3–1.5% down to ≤0.25%, primarily through variance reduction via stratification
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