On October 28, 2026, Microsoft introduced the Microsoft Copilot harness in Foundry Agent Service in public preview and announced general availability of long-running resilience for hosted agents. According to a companion post from Tina Schuchman, corporate vice president of Microsoft Foundry, and Vladimir Fedorov, CTO of GitHub, GitHub engineers built the harness that already powers Copilot Code, Copilot Studio, the GitHub Copilot app, the Copilot command-line interface (CLI), VS Code, and more; across those products the harness supports more than 20 frontier models and bring-your-own keys, while in Foundry it runs supported Foundry models that handle reasoning and tool calling. In Foundry, the harness is an optional runtime for prompt agents, with Microsoft running the agent loop and sandbox while the customer supplies instructions, skills, tools, and model. The preview bundles reusable skills; connected Foundry and Model Context Protocol (MCP) tools with configured authentication and approvals; file and code execution with built-in subagents; and agent definitions stored in source control. During the preview, Microsoft manages the approval policy for the harness’s built-in tools, the shell is on by default for new agents, Microsoft has published no export to framework code like the one AWS ships, the harness is selected when an agent is created and can’t be changed afterward, and it has no service-level agreement and isn’t recommended for production workloads. Harness runtime is free until December