Copilot Studio Agent resetting when processing PDF drawings (300MB+) via Claude 4.6 Sonnet

First thing to understand: the model is not the problem. Claude is handling the workload just fine. What is crashing is the Copilot Studio conversational runtime, which has a hard synchronous timeout of around 100 seconds per turn and strict payload size limits. A 20-minute analysis on hundreds of megabytes of files will hit that wall every time, regardless of which model you use underneath.

You cannot fix this by tweaking settings. The architecture needs to change.

I suggest you to stop passing the documents through the chat canvas. Instead, store your drawing files in SharePoint, have users reference them by link, and let Copilot Studio do only one thing: receive the request, confirm it, and kick off a Power Automate flow in the background. That flow does the actual analysis, calls the model, and when it finishes, posts the results back via Teams message or email.

The good news is that Microsoft now supports async responses for agent flows natively, meaning the flow can run well beyond the old limits and still return the result to the conversation once it is done. In your Power Automate flow, open the "Respond to the agent" action, go to Settings, and turn on Async response.

Doc: https://learn.microsoft.com/microsoft-copilot-studio/flow-asynchronous-response