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Unable to assign handlers to McpServerOptions.Handlers after upgrading to v0.9.0 (readonly regression?)

bugSomething isn't workingSomething isn't working

P2Moderate issues, valuable feature requestsModerate issues, valuable feature requests

ready for workHas enough information to startHas enough information to start

Status: Open.

#1331 In modelcontextprotocol/csharp-sdk;

· gabaoalb opened on Feb 20, 2026

Address asymmetry in McpServerHandlers/McpClientHandlers and make all filter properties settable

breaking-changeThis issue or PR introduces a breaking changeThis issue or PR introduces a breaking change

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1337

#1337 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 20, 2026

0.9.0-preview.1: ImageContentBlock throws "invalid base64" when consuming CallToolResult (works in 0.8.0-preview.1)

bugSomething isn't workingSomething isn't working

P1Significant bug affecting many usersSignificant bug affecting many users

ready for workHas enough information to startHas enough information to start

Status: Open.

#1340 In modelcontextprotocol/csharp-sdk;

· monikbhatt opened on Feb 21, 2026

Remove server back-references from protocol DTO types

breaking-changeThis issue or PR introduces a breaking changeThis issue or PR introduces a breaking change

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1345

#1345 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Fix base64 deserialization when JSON encoder escapes forward slashes

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1342

#1342 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Add CloneResourceMetadataClonesAllProperties test using public reflection

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1343

#1343 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Clarify null semantics in ToolAnnotations hint property docs

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1346

#1346 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Fix malformed XML doc on <code>McpServerPrimitiveCollection.Contains</code>

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1348

#1348 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Prevent cancellation of initialize request per MCP spec

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1350

#1350 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Make Tool.Name required to match other protocol types

breaking-changeThis issue or PR introduces a breaking changeThis issue or PR introduces a breaking change

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1351

#1351 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 21, 2026

Make LoggingMessageNotificationParams.Data required per MCP spec

breaking-changeThis issue or PR introduces a breaking changeThis issue or PR introduces a breaking change

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1353

#1353 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 22, 2026

Fix CreateMessageRequestParams.Metadata type to JsonObject

breaking-changeThis issue or PR introduces a breaking changeThis issue or PR introduces a breaking change

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1354

#1354 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 22, 2026

Increase MaxReconnectionAttempts default from 2 to 5

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1355

#1355 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 22, 2026

Fix off-by-one error in reconnection attempts

Status: Open (in progress).

modelcontextprotocol/csharp-sdknumber 1356

#1356 In modelcontextprotocol/csharp-sdk;

· Copilot opened on Feb 22, 2026