Introduction

As I have been building and delving into MCP Servers and integrating them with Microsoft 365 Copilot, I have uncovered a few more tweaks, tricks and tips and wanted to highlight a workaround for Copilot Agents built on Copilot Studio.

At the moment, there seems to be an issue with MCP servers that are holding on to state or stateful. Each time your Copilot Agent interacts with an MCP Server that holds state it creates a session ID and uses that session ID to manage interactions with the MCP Server.

I have seen issues with my custom-built MCP Servers where the session ID expires, and then the Copilot Agent is unable to interact with the MCP Server anymore. I am going to be delving more into this because I think it might be down to the fact that I need to hold onto the session ID within the MCP Server via some persistence layer, as my MCP Servers are running on serverless platforms, which are no doubt shutting down when they are not being used.

The quick workaround is to move to building stateless MCP Servers.

So, in the meantime, if you are building MCP Servers which you want to use with Copilot Studi,o I would suggest that you build them in a stateless way.

For clarity, you are seeing an example of the problem when you see errors appear like this on the backend when debugging the Copilot Studio Agent.

{

    “error”: {

        “code”: -32001,

        “message”: “Session not found”

    },

    “id”: “”,

    “jsonrpc”: “2.0”

}

The end user will likely see something like this:

Not a great experience, and the cause of the problem is not easily visible to the end user or the support person working to fix this.

As I mentioned in a previous blog post, https://simondoy.com/2025/08/29/my-adventures-in-building-and-understanding-mcp-for-microsoft-365-copilot/, I am building MCP Servers using the .NET MCP SDK and therefore, I will show you how to build your MCP Server without state. It’s fortunately really simple.

Simply change how you are configuring your HTTP transport options for your MCP Server.

That is right, the WithHttpTransport function has an override where you can pass in configuration options. One of them is Stateless,s and setting this to true will mean that your MCP Server behaves quite differently and does not go through the process of checking session IDs etc.

Here is the documentation which sets that out [https://modelcontextprotocol.github.io/csharp-sdk/api/ModelContextProtocol.AspNetCore.HttpServerTransportOptions.html].

Here is the summary from the documentation on what the Stateless property does.

If true, SessionId will be null, and the “MCP-Session-Id” header will not be used; the RunSessionHandler will be called once for each request, and the “/sse” endpoint will be disabled. Unsolicited server-to-client messages and all server-to-client requests are also unsupported, because any responses may arrive at another ASP.NET Core application process. Client sampling and root capabilities are also disabled in stateless mode, because the server cannot make requests. Defaults to false.

Once you have re-published your MCP Server with this tweak to the configuration, the issues go away as sessions with the MCP Server are not an issue any more.

Conclusion

For the time being, if you are building MCP Servers for Copilot Studio at this time I would look to build them as a stateless MCP Server. Obviously, there might be issues with some MCP Server implementations where this might not be possible, as they need state. At this time, I don’t have a solution, but I am going to add this to my list of things to look into with MCP Servers.