# Microsoft Copilot harness

Microsoft has made the Copilot harness built by GitHub engineers, already adopted company-wide, available through Microsoft Foundry so developers can build agents that reason, use tools and finish long-running tasks as a managed service. Previously, keeping up with frontier models meant building and maintaining your own harness or model router; now one harness reaches 20+ frontier models plus bring-your-own-key, with the platform routing work to the right model for the task. The harness runtime has been ported to Rust, which Microsoft says cuts session overhead and time-to-first token, and it already runs across product surfaces at the scale of millions of users.

Microsoft has made the Copilot harness built by GitHub engineers, already adopted company-wide, available through Microsoft Foundry so developers can build agents that reason, use tools and finish long-running tasks as a managed service. Previously, keeping up with frontier models meant building and maintaining your own harness or model router; now one harness reaches 20+ frontier models plus bring-your-own-key, with the platform routing work to the right model for the task. The harness runtime has been ported to Rust, which Microsoft says cuts session overhead and time-to-first token, and it already runs across product surfaces at the scale of millions of users.