Microsoft said its Copilot harness is now available through Foundry, bringing a managed runtime for multi-model agents and tool use.

Microsoft said on Oct. 28, 2026, that it is making the Microsoft Copilot harness available through Microsoft Foundry, extending a runtime it says already powers Copilot Code, Copilot Studio, the GitHub Copilot app, the CLI and VS Code. The company framed the move as a way for developers and enterprise customers to build agents that can reason, use tools and complete longer-running tasks without switching harnesses or the rest of their stack.

In Microsoft’s account, the harness is the orchestration layer around an AI model: it supplies instructions, context, execution environment and controls. The company said a harness suitable for this work also needs support for open standards such as MCP, agent skills and agent plugins. Microsoft described the field as fast moving and said maintaining a custom router or harness can be difficult because performance, quality and cost must be managed continuously.

Microsoft said the Copilot harness was built by GitHub engineers and has been standardized across its Copilot experiences. The company said the system is designed to work across model families, including “20+ frontier models” plus bring-your-own-key support, and that it automatically routes work to the right model or models for a given task. Microsoft also said it recently ported the harness runtime to Rust, which it claims improved performance and reduced both session overhead and time-to-first token.

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