The Model Context Protocol uses string-based version identifiers following the format YYYY-MM-DD, to indicate the last date backwards incompatible changes were made.
The protocol version will not be incremented when the protocol is updated, as long as the changes maintain backwards compatibility. This allows for incremental improvements while preserving interoperability.

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Revisions

Revisions may be marked as:
  • Draft: in-progress specifications, not yet ready for consumption.
  • Current: the current protocol version, which is ready for use and may continue to receive backwards compatible changes.
  • Final: past, complete specifications that will not be changed.
The current protocol version is 2025-06-18.

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Negotiation

Version negotiation happens during initialization. Clients and servers MAY support multiple protocol versions simultaneously, but they MUST agree on a single version to use for the session. The protocol provides appropriate error handling if version negotiation fails, allowing clients to gracefully terminate connections when they cannot find a version compatible with the server.