The shift towards open-source has transformed how infrastructure is built, with operating systems, containers, orchestration tools, and observability frameworks being open by default. However, the application layer, particularly billing, has lagged behind in terms of openness and flexibility. Billing is not just an integration but a foundational aspect that determines how fast companies can iterate on pricing, deal structures, and product catalog evolution. As companies grow, their billing systems become increasingly complex, with logic spreading across multiple layers of the stack, migration becoming a massive project, and innovation slowing down due to rigid systems. The author argues that billing should be treated as infrastructure, owned, customized, and understood, which is why an open-source usage-based billing platform like OpenMeter has been built to address these challenges.