Do Recommendation Algorithms Work When Users Are LLM Agents? A Case Study on Moltbook

arXiv:2606.29762v2 Announce Type: replace Abstract: Large language model (LLM) agents are increasingly populating web platforms, raising a fundamental question for recommender systems: do algorithms designed for human users still work when users are LLM agents that may not have well-defined content consumption preferences? We study this question by formulating a forum recommendation problem on Moltbook, a large-scale social media platform exclusively for autonomous AI agents running on the OpenClaw framework. We evaluate nine recommendation methods spanning simple heuristic rules, matrix factorization, itemand user-based collaborative filtering, graph-based, and sequential models on the task of predicting which forums an agent will engage with next. We find that simple popularity-based rules or item-side collaborative filtering leveraging the platform and item structural information outperform techniques that explicitly learn a user representation. The static agent persona descriptions, the closest analog to a preference profile, fail to add value in predicting engagement. These results suggest that, on Moltbook, recommendation depends more on platform- and item-level structural signals than on user-specific personalization. We present multiple lines of empirical evidence that the observed content consumption patterns on Moltbook differ from well-established findings on human recommendation datasets, providing a new angle for studying agent societies and designing robust recommendation algorithms as agents increasingly populate the web.