Version 2.0 of the MCP C# SDK now available

Microsoft has just made available the next major version of the C# SDK for Model Context Protocol (MCP) implementation. The latest SDK is available in the GitHub repo.

This version 2.0 of the SDK implements the July specification of the MCP protocol. The MCP protocol in turn uses the older JSON-RPC specification over HTTP(S) to communicate. So again, many stacked protocols on top of each other.

The two major changes in the version 2.0 of the MCP C# SDK are these two:

• stateless operation by default, and
• Multi Round-Trip Requests (MRTRs).

Of these, the latter is the interesting part: if the server needs more information from the client, it responds with an InputRequiredResult. The client can then get back to the original request, and add the missing information (for example by asking the user for input).

Even if these new version's changes are quite large, the changes are almost fully backward compatible. I haven't yet upgraded my MCP implementations to this new version, but it appears that if you have been usings the Task feature, that is something that might break between version 1.0 and 2.0.