Microsoft has announced the release of the official C# SDK for the Model Context Protocol (MCP), reaching its 1.0 milestone. The update supports the latest MCP Specification from November 2025, bringing significant improvements to how servers and clients discover authorization services and handle metadata. Developers can now build more secure, flexible, and feature-rich MCP applications using this new SDK.

Improved Authorization Server Discovery

The new SDK fully supports the 2025-11-25 MCP Specification, which introduces three ways for servers to expose their Protected Resource Metadata (PRM). These include a well-known URL derived from the server’s MCP endpoint, a root well-known URL, and the traditional resource metadata URL included in authentication headers. This makes it easier for clients to locate and authenticate with servers in various deployment scenarios.

By standardizing these discovery methods, the SDK simplifies integration and enhances security. Developers can now implement more reliable authorization flows, ensuring that applications can securely access protected resources across different environments. The discovery process has become more flexible, accommodating diverse server configurations and network setups.

New Metadata and Client Registration Features

The latest MCP spec also adds icon metadata for tools, resources, and prompts, which are now included in responses to specific list requests. This enables richer user interfaces, as applications can display icons alongside resources for better clarity and branding. Additionally, implementation metadata now supports icons and website URLs, providing more context about clients and servers.

A notable change is the introduction of Client ID Metadata Documents (CIMDs). These serve as an alternative to Dynamic Client Registration (DCR) for establishing client identities with authorization servers. CIMDs are now the preferred method, streamlining the registration process and reducing complexity for developers building MCP clients and servers.

Enhanced Support for Long-Running and Sampling Requests

The 2025-11-25 MCP Specification introduces new capabilities for handling long-running operations. Servers can now include tools in sampling requests, which large language models (LLMs) may invoke to generate responses or perform tasks. This opens up new possibilities for building intelligent, interactive applications that leverage MCP’s extensibility.

For requests that take a long time to complete, the SDK and specification improve the handling of HTTP polling. Servers can initiate a server-sent event stream with an initial event that contains an event ID. Clients can then reconnect using this ID if the connection drops, ensuring reliable communication even in unstable network conditions. This change makes long-running operations more resilient and easier to manage.

Introducing Tasks for Durable State and Deferred Results

One of the most exciting features in the new SDK is the addition of tasks, which are still experimental. These provide durable state tracking and allow clients to retrieve results later, rather than waiting synchronously for a response. This is especially useful for complex or resource-intensive operations that require time to complete.

Overall, MCP C# SDK 1.0 marks a major step forward for developers working with MCP in the .NET environment. It simplifies discovery, improves metadata handling, and introduces new capabilities that boost the power and flexibility of MCP applications. Microsoft’s ongoing enhancements aim to make building secure, scalable, and intelligent MCP-based systems easier than ever before.

Inspired by

• https://www.infoworld.com/article/4141959/mcp-c-sharp-sdk-1-0-arrives-with-improved-authorization-server-discovery.html

Sources

• modelcontextprotocol.io
• microsoft.com
• github.com