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News · 2026-10-30

Microsoft opens the GitHub-built Copilot harness to external developers through Foundry Agent Service

On 28 October 2026 at GitHub Universe, Microsoft released the Copilot harness — the multi-model orchestration layer built by GitHub engineers that already powers Copilot Code, Copilot Studio, the GitHub Copilot app, the Copilot CLI and VS Code — to external developers through Foundry Agent Service in public preview. The harness supports more than 20 frontier models plus bring-your-own-key, routes work to models based on the task, and ships with the open standards it runs on: MCP, agent skills and agent plugins. Microsoft runs the agent loop and sandbox with governance built in; developers bring instructions, skills, tools and model choice, either self-hosting via the downloadable Copilot SDK or running managed in Foundry's cloud. The runtime was ported to Rust, which Microsoft credits with reduced session overhead and faster time-to-first-token. Preview use is free of harness charges, with consumption-based billing beginning 1 December 2026; model inference and some connected tools are billed separately.

What it means for buyers

Microsoft is selling the routing-and-orchestration layer itself, not just agents: a managed multi-model runtime with the same routing GitHub ships in Copilot, priced on consumption from 1 December. That puts it in direct competition with the dedicated routing layers in our ai-model-routing comparison and gives agent builders in our ai-agent-builders comparison a platform-scale default to weigh against assembling their own stack.

Where to check it

Sources

  1. Introducing the Microsoft Copilot harness: Unlocking the potential of truly multi-model agentic work (Official Microsoft Blog) — 28 October 2026, Schuchman and Fedorov: harness scope, 20+ models plus BYOK, MCP and agent skills, SDK availability, checked 2026-10-30
  2. Introducing the Microsoft Copilot harness in Foundry Agent Service (Microsoft Foundry blog) — public preview announcement: managed execution, preview limits, checked 2026-10-30
  3. Microsoft's new Copilot harness makes agents easy — until you want to switch (The New Stack) — 29 October 2026: free until 1 December 2026, model inference billed separately, checked 2026-10-30