Enterprises face significant challenges in adopting artificial intelligence (AI) due to resource constraints and lack of technical expertise. However, the rise of Artificial-Intelligence-as-a-Service (AIaaS) enables companies to access scalable AI capabilities and integrate them into their services. This study explores the emerging role of companies as mediators that bridge AI baseline services with market demands to deliver AI-powered service solutions. Using a taxonomy development approach and leveraging service modularity as a conceptual lens, we identify 13 dimensions and 56 characteristics that define the mediator role, spanning technical, organizational, and service-oriented aspects. The taxonomy provides a decision space for companies to strategically design, configure, and differentiate their AIaaS-powered service solutions. The taxonomy supports practitioners in crafting effective AIaaS mediation strategies and offers researchers a structured framework to investigate the socio-technical interplay of AI capability utilization and service value creation.