# News: 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.

Human page: https://testedactually.com/news/microsoft-copilot-harness-foundry/
Mirror: https://testedactually.com/news/microsoft-copilot-harness-foundry.md
Published: 2026-10-30

## What changed

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.

## Sources

- [1] Introducing the Microsoft Copilot harness: Unlocking the potential of truly multi-model agentic work (Official Microsoft Blog) - https://blogs.microsoft.com/blog/2026/10/28/introducing-the-microsoft-copilot-harness-unlocking-the-potential-of-truly-multi-model-agentic-work/ (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) - https://devblogs.microsoft.com/foundry/microsoft-copilot-harness-in-foundry/ (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) - https://thenewstack.io/microsoft-copilot-harness-foundry/ (29 October 2026: free until 1 December 2026, model inference billed separately, checked 2026-10-30)

TestedActually tracks pricing and programme changes as dated, sourced events: https://testedactually.com/news/.