OpenAI has rapidly transformed into a powerhouse, generating billions in revenue in just three years after launching ChatGPT. Sara Conlon, Head of Financial Engineering at OpenAI, spoke at Monetize 2025 about the company's journey and the systems that support its fast-paced monetization. She emphasized the importance of a centralized billing infrastructure, which replaced the previous decentralized model that led to inefficiencies, inconsistencies, and operational challenges. The centralized Financial Engineering team now streamlines billing processes and reduces risks by creating reusable components for product teams, ensuring a consistent experience for customers. Conlon introduced a balanced approach to billing design, focusing on intention (providing customer value) and control (protecting the business). This dual focus helps in creating features that serve both customer needs and business requirements. The Financial Engineering team is organized into four specialized pods: Pricing & Packaging, Infrastructure, Financial Automation, and Payments. Each pod has distinct responsibilities but works collectively to enhance the overall monetization strategy. This structure reflects a trend in the industry where specialized teams can adapt and evolve more effectively than a monolithic approach. The evolution of billing teams typically moves through three phases: survival, advising, and proactive. In the survival phase, speed takes precedence, often compromising system integrity. As teams mature, they begin to consult billing for guidance. The goal is to reach a proactive phase where billing informs strategy and anticipates needs. Conlon shared lessons from OpenAI’s hypergrowth, particularly the need to modularize billing to prevent issues like the overwhelming of infrastructure during rapid account creation. This shift from a subscription model to usage-based billing aligns with broader industry trends, emphasizing the importance of monetization as core infrastructure rather than a secondary concern.