Key Changes

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Major changes

1. Enhance authorization server discovery with support for OpenID Connect Discovery 1.0. (PR #797)
2. Allow servers to expose icons as additional metadata for tools, resources, resource templates, and prompts (SEP-973).
3. Enhance authorization flows with incremental scope consent via WWW-Authenticate (SEP-835)
4. Provide guidance on tool names (SEP-986)
5. Update ElicitResult and EnumSchema to use a more standards-based approach and support titled, untitled, single-select, and multi-select enums (SEP-1330).
6. Added support for URL mode elicitation (SEP-1036)
7. Add tool calling support to sampling via tools and toolChoice parameters (SEP-1577)
8. Add support for OAuth Client ID Metadata Documents as a recommended client registration mechanism (SEP-991, PR #1296)
9. Add experimental support for tasks to enable tracking durable requests with polling and deferred result retrieval (SEP-1686).

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Minor changes

1. Add optional description field to Implementation interface to align with MCP registry server.json format and provide human-readable context during initialization.
2. Clarify that servers must respond with HTTP 403 Forbidden for invalid Origin headers in Streamable HTTP transport. (PR #1439)
3. Updated the Security Best Practices guidance.
4. Clarify that input validation errors should be returned as Tool Execution Errors rather than Protocol Errors to enable model self-correction (SEP-1303).
5. Support polling SSE streams by allowing servers to disconnect at will (SEP-1699).
6. Clarify SEP-1699: GET streams support polling, resumption always via GET regardless of stream origin, event IDs should encode stream identity, disconnection includes server-initiated closure (Issue #1847).
7. Align OAuth 2.0 Protected Resource Metadata discovery with RFC 9728, making WWW-Authenticate header optional with fallback to .well-known endpoint (SEP-985).
8. Add support for default values in all primitive types (string, number, enum) for elicitation schemas (SEP-1034).
9. Establish JSON Schema 2020-12 as the default dialect for MCP schema definitions (SEP-1613).

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Other schema changes

1. Decouple request payloads from RPC method definitions into standalone parameter schemas. (SEP-1319, PR #1284)

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Governance and process updates

1. Formalize Model Context Protocol governance structure (SEP-932).
2. Establish shared communication practices and guidelines for the MCP community (SEP-994).
3. Formalize Working Groups and Interest Groups in MCP governance (SEP-1302).
4. Establish SDK tiering system with clear requirements for feature support and maintenance commitments (SEP-1730).

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Full changelog