Online Recommender Systems: Is the Juice Worth the Squeeze? Keynote Eugene Yan1 1 Amazon, Seattle, WA, USA Abstract Online recommender systems are increasingly prevalent given their ability to adapt to the customer’s needs in real time. Nonetheless, they come with additional costs (computation, operational) and complex- ity (infrastructure). In this keynote, we explore when it makes sense to use an online recommender and when a batch recommender is good enough. Then, to better understand the differentiating strengths of online recommenders, we share three systems at Amazon Books that play to these strengths, high-level results, and lessons from making them work in the field. Speaker biography Eugene Yan is a Senior Applied Scientist at Amazon where he builds machine learning and recommender systems. His interests lie in applying machine learning to industrial systems that serve customers at scale. His current work at Amazon focuses on session-based candidate retrieval, bandit-based ranking, and recommendations in search. Previously, he led the data science teams at Lazada (acquired by Alibaba) and uCare.ai (Series A healthtech). ORSUM@ACM RecSys 2022: 5th Workshop on Online Recommender Systems and User Modeling, jointly with the 16th ACM Conference on Recommender Systems, September 23rd, 2022, Seattle, WA, USA © 2022 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0). CEUR Workshop Proceedings http://ceur-ws.org ISSN 1613-0073 CEUR Workshop Proceedings (CEUR-WS.org)