Production-grade AI agents are built on two foundational pillars: the Core AI stack, which ensures intelligence and differentiation, and the Reliability stack, which guarantees safety, consistency, and trustworthiness. The Core AI stack involves rapidly evolving components such as models, prompts, and data pipelines, which drive an agent's reasoning, planning, and action capabilities. In contrast, the Reliability stack involves systems like guardrails, monitoring, and human-in-the-loop processes to maintain the agent's dependable performance at scale. Successful teams invest in developing their Core AI stack to maintain a competitive edge while standardizing the Reliability stack to avoid firefighting and ensure seamless scalability. This separation allows for faster innovation and adaptation, as demonstrated by enterprises that have successfully adopted new capabilities by owning their Core AI components, while those who failed to do so lagged behind. Reliability infrastructure is essential for handling issues such as incorrect outputs, proactive alerting, and integrating non-technical human oversight to continuously improve AI performance. Ultimately, the best AI agents are those that combine intelligence with trust, achieved by owning the Core and standardizing the Reliability stack.