v1.0.0-rc.1

This release candidate completes a full API surface area audit ahead of the 1.0.0 stable release, with more changes to public APIs to ensure consistency and long-term maintainability. Protocol DTO types are updated to match the MCP specification, deprecated filter APIs are removed, and bug fixes improve transport reliability and JSON handling.

Breaking Changes

Refer to the C# SDK Versioning documentation for details on versioning and breaking change policies.

1. Address asymmetry in McpServerHandlers/McpClientHandlers and make all filter properties settable #1337

   • Seals McpClientHandlers to match the already-sealed McpServerHandlers
   • Makes McpServerOptions.Handlers, McpServerOptions.Filters, and all IList<T> filter properties settable with null validation

2. Remove server back-references from protocol DTO types #1345

   • Removes Tool.McpServerTool, Prompt.McpServerPrompt, Resource.McpServerResource, and ResourceTemplate.McpServerResource properties
   • Use McpServerPrimitiveCollection.TryGetPrimitive() for name-based lookups instead

3. Make Tool.Name required to match other protocol types #1351

   • Adds required modifier to Tool.Name, matching Prompt.Name, Resource.Name, and other IBaseMetadata implementations
   • Callers must now specify Name in object initializers

4. Make LoggingMessageNotificationParams.Data required per MCP spec #1353

   • Changes LoggingMessageNotificationParams.Data from JsonElement? to required JsonElement per the MCP specification

5. Fix CreateMessageRequestParams.Metadata type to JsonObject #1354

   • Changes CreateMessageRequestParams.Metadata from JsonElement? to JsonObject? to match all other _meta/Meta properties in the SDK

6. Normalize CallToolResult.StructuredContent to JsonElement? #1357

   • Changes CallToolResult.StructuredContent from JsonNode? to JsonElement? for consistency with the rest of the SDK
   • Use JsonSerializer.SerializeToElement() to produce a JsonElement

7. Unify service configuration for ISseEventStreamStore, IMcpTaskStore, and ISessionMigrationHandler #1362

   • Consistent options + DI pattern: explicit options property > DI resolution

8. Add explicit [Experimental] protected constructors to McpClient and McpServer #1363

   • Protected constructors on McpClient and McpServer now require suppressing MCPEXP002 to subclass

9. Remove MCP9002 obsolete APIs and document obsolete diagnostics #1366

   • Removes the 13 AddXxxFilter extension methods on IMcpServerBuilder (e.g. AddCallToolFilter, AddListToolsFilter) that were deprecated under diagnostic MCP9002
   • Use WithRequestFilters() and WithMessageFilters() instead

10. Fix McpClientPrompt/Resource types to use RequestOptions like McpClientTool does #1370

    • Replaces JsonSerializerOptions with RequestOptions parameter for consistency across McpClientPrompt, McpClientResource, and McpClientTool

What's Changed

• Make Tool.Name required to match other protocol types #1351 by @stephentoub (co-authored by @Copilot)
• Make LoggingMessageNotificationParams.Data required per MCP spec #1353 by @stephentoub (co-authored by @Copilot)
• Fix off-by-one error in reconnection attempts #1356 by @stephentoub (co-authored by @Copilot)
• Remove server back-references from protocol DTO types #1345 by @stephentoub (co-authored by @Copilot)
• Fix base64 deserialization when JSON encoder escapes forward slashes #1342 by @stephentoub (co-authored by @Copilot)
• Increase MaxReconnectionAttempts default from 2 to 5 #1355 by @stephentoub (co-authored by @Copilot)
• Prevent cancellation of initialize request per MCP spec #1350 by @stephentoub (co-authored by @Copilot)
• Address asymmetry in McpServerHandlers/McpClientHandlers and make all filter properties settable #1337 by @stephentoub (co-authored by @Copilot)
• Normalize CallToolResult.StructuredContent to JsonElement? #1357 by @stephentoub (co-authored by @Copilot)
• Fix CreateMessageRequestParams.Metadata type to JsonObject #1354 by @stephentoub (co-authored by @Copilot)
• Remove MCP9002 obsolete APIs and document obsolete diagnostics #1366 by @jeffhandley (co-authored by @Copilot)
• Add explicit [Experimental] protected constructors to McpClient and McpServer #1363 by @stephentoub (co-authored by @Copilot @jeffhandley)
• Fix McpClientPrompt/Resource types to use RequestOptions like McpClientTool does #1370 by @stephentoub (co-authored by @Copilot)
• Unify service configuration for ISseEventStreamStore, IMcpTaskStore, and ISessionMigrationHandler #1362 by @MackinnonBuck

Documentation Updates

• Fix malformed XML doc on McpServerPrimitiveCollection.Contains #1348 by @stephentoub (co-authored by @Copilot)
• Clarify null semantics in ToolAnnotations hint property docs #1346 by @stephentoub (co-authored by @Copilot)
• Fix compilation errors in README code samples #1369 by @jeffhandley
• Fix XML documentation spelling, grammar, and correctness issues across SDK #1372 by @stephentoub (co-authored by @Copilot)
• Add Roadmap document and navigation link #1373 by @jeffhandley

Test Improvements

• Add CloneResourceMetadataClonesAllProperties test using public reflection #1343 by @stephentoub (co-authored by @Copilot)

Repository Infrastructure Updates

• Bump version to 1.0.0-rc.1 #1376 by @jeffhandley
• Add README code sample validation step to release-notes skill #1371 by @jeffhandley
• Bump the other-testing group with 1 update #1358
• Bump Anthropic from 12.5.0 to 12.8.0 #1359

Acknowledgements

• @monikbhatt submitted issue #1340 (resolved by #1342)
• @gabaoalb submitted issue #1331 (resolved by #1337)
• @halter73 @MackinnonBuck @ericstj reviewed pull requests

Full Changelog: v0.9.0-preview.2...v1.0.0-rc.1