Pinner Progression: Better Use-Case Representation Driving Weekly Active User Growth at Pinterest

This post introduces User Interest Clusters (UICs) as a new stateful interest representation to augment sequential user understanding with holistic, persistent use-case representation for retention. It details the construction of UICs using Complete Linkage Agglomerative Hierarchical Clustering on engaged Pins within the OmniSage embedding space, allowing for personalized clustering, dynamic cluster counts, and stateful lifecycle metadata. The post also outlines the system-level integration of UICs across the recommendation serving stack (retrieval, scoring, ranking, blending) to drive retention by treating interests based on their maturity and fostering serendipitous discovery.