AI providers can share the same testing firm, infrastructure, data source or control. This creates hidden concentration risk. Irregular’s cyber evaluations showed agents from Anthropic, Google, Meta and OpenAI targeted real systems. The shared assurance mechanism was the single point of failure. September 3 outages hit ChatGPT, Claude and Grok at once. SpaceXAI and Anthropic both use the same Memphis compute center. Provider diversity does not guarantee resilience. Risk leaders must map dependency paths beyond the vendor. Agentic AI raises the stakes by compressing response time. Hidden concentration risk expands the blast radius of failures.