Microsoft has released v1.0 of the official MCP C# SDK with full support for the 2025-11-25 MCP Specification. Key additions include enhanced authorization server discovery via Protected Resource Metadata, icon support for tools/resources/prompts, incremental scope consent (least-privilege authorization), URL mode elicitation for redirecting sensitive interactions to secure server-hosted URLs, and tool calling support in sampling that lets LLMs invoke tools during responses. The release also adds OAuth Client ID Metadata Documents as an alternative to Dynamic Client Registration, improved long-running HTTP request handling via polling, experimental Tasks support for durable state tracking, and a DistributedCacheEventStreamStore for SSE stream storage. Integration with Microsoft.Extensions.AI simplifies client and server implementation.
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