Microsoft announced on its official blog on October 28, 2026 that the Microsoft Copilot harness, the agent layer behind its Copilot products, is now available to developers and enterprise customers through Microsoft Foundry. The post was written by Tina Schuchman, a Microsoft corporate vice president for Foundry, and Vladimir Fedorov, GitHub’s CTO.

The Copilot harness is the code that runs around an AI model. It feeds the model its instructions, calls tools, keeps the session going and decides which model handles which step. Microsoft says GitHub’s engineers built it, and it already runs GitHub Copilot, Copilot Studio and its coding tools.

What’s new

  • Available as a managed service in Microsoft Foundry, or as an SDK you can download from GitHub.
  • Supports more than 20 frontier models plus bring-your-own-key, and routes each task to a model that suits it.
  • Works with open standards including MCP, agent skills and agent plugins.
  • Microsoft says it rewrote the runtime in Rust to cut session overhead and time to first token.
  • Microsoft runs the agent loop and the sandbox. Customers bring the instructions, skills, tools and model choice.
  • The post gives no pricing and doesn’t describe any change for Microsoft 365 Copilot plans.

Who it affects

Developers and companies building their own AI agents on Microsoft’s cloud. A small business using Microsoft 365 Copilot or Copilot Studio as-is doesn’t need to do anything, since nothing in the announcement changes those plans.

It matters more if you’re paying someone to build a custom agent. It gives your developer a ready-made, multi-model layer to build on instead of a hand-rolled one, which should make switching models later less painful.

Our take

For most small teams this is background news. If an agent project is on your list for next year, ask whoever builds it two questions: can the agent switch models without a rebuild, and does it use MCP so your other tools can plug in later. The Copilot harness is one way to get both. It isn’t the only one, and we’d wait for Foundry pricing before committing to it.

Weighing up an agent? Start with our guide to AI agents versus plain automation, or see how we build AI agents for small businesses that connect to the tools and APIs you already use.