A new infrastructure category is emerging as major AI players including Cursor, OpenAI, Anthropic, and Microsoft move beyond language models to develop "harness-as-a-service" platforms that provide complete runtime environments for AI agents. Rather than requiring developers to assemble agent capabilities from individual components, these platforms offer pre-built operational frameworks that handle the complex coordination and execution logic agents need to function effectively. The shift represents a fundamental change in how agentic applications will be built and deployed. By renting managed runtime environments instead of constructing every piece independently, developers can significantly reduce complexity and time-to-market. This approach is expected to define the next wave of agentic applications, similar to how platform-as-a-service (PaaS) transformed cloud computing. The infrastructure trend coincided with strong quarterly earnings from Google, Amazon, Microsoft, and Meta, underscoring the commercial momentum behind AI infrastructure investments.