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Whatever you build in Microsoft Copilot Studio, a harness powers it behind the scenes. You design your agent or workflow, while the model you select supplies the reasoning and generation. The harness is a runtime that exists between the two: it determines when to call the model, what components to send it, interprets what comes back, and calls the right tools.
Note
Different harnesses use different billing methods:
- Agents and workflows powered by the GitHub Copilot harness use Copilot Credits for usage-based billing.
- Agents powered by the standard harness or Copilot chat harness and agent flows use licensing and billing described in Licensing for agents powered by the standard harness.
What runs on a harness
Everything you build in Copilot Studio runs on a harness:
- The GitHub Copilot harness powers agents and workflows built for reasoning-heavy, multi-step work.
- The standard harness powers rule-based agents and agent flows.
- The Copilot chat harness for extending Microsoft 365 Copilot.
The rest of this article focuses on how the three harnesses differ so you can choose the right one for what you're building.
Why the harness matters
The harness you build on affects several things you care about as a builder:
- How your work gets done. Some harnesses follow the rules, branches, and steps you define in an agent or workflow. Others can take a goal, break it into steps, and adjust as they go.
- How much work you can automate end to end. A more capable harness can handle longer, multistep business processes across tools, files, and intermediate decisions, and recover when something doesn't go as planned.
- What experiences you can build out of the box. Capabilities like creating and editing files, using skills, remembering context, and orchestrating tool calls depend on the harness.
- How your usage is billed. Different harnesses use different pricing. See Copilot Studio licensing.
Choose between harnesses
GitHub Copilot harness – The most capable option, built for reasoning-heavy agents and workflows that need to complete complex business processes. Instead of following only a fixed script, it can take a goal, break it into steps, call the right tools across connectors, knowledge, MCP, and connected agents, and adjust when a step fails or a request changes. It natively creates and edits Word, Excel, PowerPoint, and PDF files, supports skills and memory, and runs each task in a secure sandbox governed by Copilot Studio. Agents and workflows on this harness use Copilot Credits. It's the best fit for scenarios such as an accounts payable process, where an agent or workflow reads invoices, matches them to purchase orders, and routes exceptions for approval.
Standard harness – A dependable option for rule-based agents and structured, repeatable workflows or conversations, where you want predictable behavior for well-understood requests. You define the topics, prompts, and paths so the experience responds consistently, and it can draw on your existing prompt library and enterprise knowledge. It's a good fit for scenarios such as an internal help-desk experience that answers common questions and routes simple requests through a workflow.
Copilot chat harness – The harness for extending Microsoft 365 Copilot Chat. Connect your enterprise knowledge to M365 Copilot Chat so employees get answers grounded in your content without leaving their everyday experience. It runs on current chat models and is designed for scenarios where the priority is connecting people to information, such as an employee onboarding agent that answers questions from SharePoint knowledge. Publish to internal teams. Billing is consumption-based or included in Microsoft 365 Copilot user subscription license.
Choose the GitHub Copilot harness when your agent needs to reason through longer tasks, work across several tools, handle files, or automate a real business process end to end. Choose the standard harness when your scenario is well-defined and rule-based, and you want consistent, predictable answers. Choose the Copilot chat harness when your goal is to extend Microsoft 365 Copilot Chat with your organization's knowledge so employees get grounded answers without leaving their everyday experience.
| Considerations | GitHub Copilot harness | Standard harness | Copilot chat harness |
|---|---|---|---|
| Best for | Complex, multi-step business processes | Rule-based agents and structured conversations | Extending M365 Copilot Chat with enterprise knowledge |
| How it works | Reasons through a goal on its own, step by step | Follows the topics and rules you define | Connects enterprise knowledge to M365 Copilot Chat |
| Recovers from problems | Retries and finds alternative paths automatically | Follows the paths you've built | Not a focus |
| Works with files | Creates, edits, and reasons over Word, Excel, PowerPoint, and PDF files | Not a focus | Not a focus |
| Skills and memory | Yes | Not a focus | Not a focus |
| Publishing | Internal teams or external customers | Internal teams or external customers | Internal teams |
| Billing | Copilot Credits | See Copilot Studio licensing | Consumption or included in M365 Copilot USLs |