C# SDK v2.2.0 adds hybrid HTTP serving so 2025-11-25 and 2026-07-28 clients share one endpoint
The official MCP C# SDK released v2.2.0 on 2026-08-13, adding an HttpServerSessionMode for hybrid stateful/stateless HTTP serving so clients on the 2025-11-25 and 2026-07-28 protocol revisions can share an endpoint, and fixing a header-decoding edge case in McpHeaderEncoder.DecodeValue.
The official MCP C# SDK released v2.2.0 on 2026-08-13. The headline
change is HttpServerSessionMode, a hybrid stateful/stateless HTTP
serving mode added in pull request #1796, which lets clients speaking
the 2025-11-25 revision and the stateless
2026-07-28 revision share a single endpoint during
the migration window.
The release also fixes an edge case in McpHeaderEncoder.DecodeValue,
which previously threw on a degenerate base64 wrapper (#1805), and
enables package validation for the MCP extension packages in the
repository's release infrastructure.
v2.2.0 follows three weeks after v2.1.0 added the public subscriptions/listen server handler on 2026-08-05, continuing the SDK's incremental build-out of 2026-07-28 serving features.
Related spec revisions
- MCP 2026-07-28 - current
- MCP 2025-11-25 - superseded
How was this verified, and what are the sources?
Published · confidence 1.00.