APIs are no longer just integration layers. They power customer logins, payment processing, SaaS workflows, partner ecosystems, and mobile applications. When an API becomes unavailable, revenue stops, user trust declines, and service level agreements are immediately at risk. Yet many teams still define API availability in the simplest possible way. If an endpoint responds with a 200 OK, the API is considered available. Monitoring dashboards stay green. Alerts remain silent. Everything appears healthy.