ByteByteGo published an interview-based technical breakdown with Marco Casalaina, VP of Products for Microsoft Core AI, on how Microsoft builds and operates production AI agents. It states that more than 80,000 enterprises build on Microsoft Foundry, that Microsoft 365 Copilot serves over 20 million users with monthly active usage of first-party agents growing 6x year-to-date, and that Foundry offers access to more than 11,000 models from OpenAI, Anthropic, xAI, DeepSeek and Microsoft's MAI family. Casalaina's central claim is that "the harness matters as much as the model": the runtime, tools, context retrieval, identity (via Entra), guardrails, observability (Foundry Control Plane routing telemetry to Azure Monitor and Application Insights) and evaluation layers.