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The latest listed MCP C# SDK release is v2.2.0, published August 13, 2026. It adds hybrid stateful and stateless HTTP serving for clients using protocol revisions 2025-11-25 and 2026-07-28; it does not introduce a newer protocol revision. The major alignment with the 2026-07-28 MCP specification arrived earlier, in SDK v2.0.0. The v2 SDK line also remains compatible with older peers, subject to a specific exception for Tasks.
What changed in the latest MCP C# SDK?
Release v2.2.0 adds HttpServerSessionMode, which lets an HTTP server support stateful and stateless sessions through the same endpoint. That is useful when clients using protocol revisions 2025-11-25 and 2026-07-28 need to connect to one server endpoint. The release also fixes an edge case involving malformed header decoding. See the official v2.2.0 release notes.
This is an SDK release that improves mixed-version HTTP serving, not a new MCP specification update. SDK v2.0.0 established stable alignment with specification revision 2026-07-28. The SDK versioning guide says the v2 line can negotiate with peers using 2025-11-25 and earlier revisions.
What does support for MCP 2026-07-28 mean?
The 2026-07-28 protocol revision shifts the connection model toward discovery-first negotiation and stateless operation, reducing reliance on initialization handshakes and server-side session state. The official announcement also describes Multi Round-Trip Requests, standardized headers and caching hints. MCP Apps and Tasks are available as extension packages rather than being bundled as core protocol behavior. The MCP specification announcement calls the release “MCP’s most important since remote MCP first launched over a year ago,” according to David Soria Parra, Member of Technical Staff and MCP co-inventor.
#1 Best Overall
For ordinary older peers, the SDK falls back to the legacy initialize handshake. That compatibility does not extend equally to every extension: Tasks in the v2 SDK require negotiation of protocol revision 2026-07-28 or later, and the current Tasks extension has no API or wire compatibility with the earlier experimental Tasks implementation. Microsoft’s .NET SDK announcement also describes stateless-by-default deployment and ongoing authentication and authorization work.
SDK 1.x and 2.x: what should you compare?
Before upgrading, compare the protocol and API features your application actually uses rather than treating the major-version change as a simple package swap.
| Area | What to verify |
|---|---|
| Protocol revision | SDK v2 aligns with 2026-07-28 and remains compatible with peers negotiating 2025-11-25 and earlier; confirm the revisions your client or server must support. |
| Connection and HTTP sessions | Determine whether your server needs stateful, stateless or mixed HTTP behavior. SDK v2.2.0 adds HttpServerSessionMode for hybrid serving across the 2025-11-25 and 2026-07-28 revisions. |
| Tasks | Plan for the v2 Tasks extension’s protocol requirement and its incompatibility with the earlier experimental Tasks implementation. |
| Experimental APIs | Identify APIs marked [Experimental]; their changes are not restricted to major-version releases. |
| Migration effort | Check your existing initialization flow, extension use, package references and the release notes for changes relevant to your application. |
Which MCP C# package should you use?
Choose packages according to your application’s architecture. The official SDK README describes the package roles and links to documentation and samples.
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Quick Recap
Rank #4
| Package | Use it when |
|---|---|
ModelContextProtocol.Core |
You need low-level MCP APIs and want to keep dependencies to a minimum. |
ModelContextProtocol |
You want hosting and dependency-injection support and do not need HTTP server capabilities. This is the usual choice for that setup. |
ModelContextProtocol.AspNetCore |
You are building an HTTP-based MCP server. |
| Apps and Tasks extension packages | Your project needs those separate MCP extensions; review their protocol and compatibility requirements before adding them. |
What to check before upgrading
- Confirm the installed and target versions. The latest listed release is v2.2.0, while protocol alignment with 2026-07-28 began in v2.0.0. Check the official release list for updates after that release.
- Check the peer and transport. Verify the protocol revisions supported by the clients or servers you connect to, and whether your HTTP endpoint needs the hybrid session mode introduced in v2.2.0.
- Audit extension and experimental API use. Tasks require 2026-07-28 or later in the v2 extension and are not compatible with the earlier experimental Tasks API. APIs marked
[Experimental]may change even in a patch or minor release. - Select only the packages your design needs. Decide whether you need low-level APIs, hosting and dependency injection, HTTP server support, Apps or Tasks.
- Read the versioning guide and release notes before changing package references. The SDK uses Semantic Versioning, but experimental APIs have a separate stability caveat. Follow the versioning guidance alongside the notes for the versions you are moving between.
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