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This document lists changes made to the Model Context Protocol (MCP) specification since the previous revision, 2025-11-25.

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Major changes

N/A

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Minor changes

  1. Add extensions field to ClientCapabilities and ServerCapabilities to support optional extensions beyond the core protocol.
  2. Document OpenTelemetry trace context propagation conventions for _meta keys (traceparent, tracestate, baggage) (SEP-414).
  3. Servers SHOULD return tools from tools/list in a deterministic order to enable client-side caching and improve LLM prompt cache hit rates.
  4. Require standard MCP request headers (Mcp-Method, Mcp-Name) on Streamable HTTP POST requests, and add support for custom headers from tool parameters via x-mcp-header (SEP-2243).

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Other schema changes

N/A

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Governance and process updates

N/A

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Process changes

  1. Formalize PR-based SEP workflow with markdown files in seps/ directory, PR-derived numbering, sponsor responsibilities, and status management via PR labels (SEP-1850).

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Full changelog

For a complete list of all changes that have been made since the last protocol revision, see GitHub.