v0.2.0-preview.3

This release introduces the ModelContextProtocol.Core package, splitting the SDK into layered packages to provide client and low-level server APIs with minimal dependencies. Protocol record types are converted to classes for better forward compatibility, elicitation support is added, and protocol version negotiation is improved.

Breaking Changes

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

1. Add ModelContextProtocol.Core package #428
   • Client, protocol, transport, and core types moved from the ModelContextProtocol assembly to a new ModelContextProtocol.Core assembly; existing ModelContextProtocol package now references ModelContextProtocol.Core and provides hosting/DI extensions
   • Migration: Applications referencing ModelContextProtocol retain access to all types with no changes needed; applications wanting minimal dependencies can reference ModelContextProtocol.Core directly
2. Convert records to classes #470
   • Nine protocol types converted from record/record struct to class: SseClientTransportOptions, StdioClientTransportOptions, ProgressNotificationValue, Annotations, InitializeResult, JsonRpcErrorDetail, PingResult, Resource, ResourceTemplate; ProgressNotificationValue changed from value type to reference type
   • Migration: Remove uses of structural equality, with expressions, and deconstruction on the affected types
3. Improve protocol version handling #468
   • McpClientOptions.ProtocolVersion and McpServerOptions.ProtocolVersion changed from string to string?; default protocol version updated from 2024-11-05 to 2025-03-26; server now negotiates the protocol version based on the client's requested version
   • Migration: Update any code that relies on the ProtocolVersion type or the default protocol version value

What's Changed

• Add elicitation capability #467 by @stephentoub
• Convert records to classes #470 by @eiriktsarpalis
• Add ModelContextProtocol.Core package #428 by @halter73
• Improve protocol version handling #468 by @stephentoub
• Don't conflate request and response IDs in Streamable HTTP transports #475 by @halter73

Repository Infrastructure Updates

• Bump version to 0.2.0-preview.3 #465 by @jeffhandley
• Convert solution to slnx #472 by @eiriktsarpalis
• Update dependency versions #474 by @stephentoub

Acknowledgements

• @mkeeley-tricentis submitted issue #464 (resolved by #475)
• @ladeak reviewed pull requests

Full Changelog: v0.2.0-preview.2...v0.2.0-preview.3