Truthful Aggregation of LLMs with an Application to Online Advertising

Online platforms generate hundreds of billions of dollars in revenue per year by showing advertisements alongside their own content. Currently, these platforms are integrating Large Language Models (LLMs) into their services. This makes revenue generation from LLM-generated content the next major challenge in online advertising. We consider a scenario where advertisers aim to influence the responses of an LLM to align with their interests, while platforms seek to maximize advertiser value and ensure user satisfaction. We introduce an auction mechanism for this problem that operates without LLM fine-tuning or access to model weights and provably converges to the output of the optimally fine-tuned LLM for the platform's objective as computational resources increase. Our mechanism ensures that truthful reporting is a dominant strategy for advertisers and it aligns each advertiser's utility with their contribution to social welfare - an essential feature for long-term viability. Additionally, it can incorporate contextual information about the advertisers, significantly accelerating convergence. Via experiments with a publicly available LLM, we show that our mechanism significantly boosts advertiser value and platform revenue, with low computational overhead. While our motivating application is online advertising, our mechanism can be applied in any setting with monetary transfers, making it a general-purpose solution for truthfully aggregating the preferences of self-interested agents over LLM-generated replies.