From Scoring to Spelling: Rebuilding Ads Retrieval at Instacart (12 minute read) (opens in new tab)

Instacart rebuilt its ads retrieval system by moving from a scoring-based BERT model (that scored every product ID) to a generative approach that “spells out” recommendations token-by-token using Instacart Semantic IDs. This shift solved vocabulary bottlenecks, cold-start problems, and structural drift, enabling better generalization, full catalog coverage, and stronger session understanding.