Key Changes changedspecification/2025-06-18/changelog
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11# Key Changes
22
33This document lists changes made to the Model Context Protocol (MCP) specification since
4the previous revision, [2025-03-26](/specification/2025-03-26).
4the previous revision, [2025-03-26](/specification/2025-03-26.md).
55
66## Major changes
77
881. Remove support for JSON-RPC **[batching](https://www.jsonrpc.org/specification#batch)**
99 (PR [#416](https://github.com/modelcontextprotocol/specification/pull/416))
102. Add support for [structured tool output](/specification/2025-06-18/server/tools#structured-content)
102. Add support for [structured tool output](/specification/2025-06-18/server/tools.md#structured-content)
1111 (PR [#371](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/371))
123. Classify MCP servers as [OAuth Resource Servers](/specification/2025-06-18/basic/authorization#authorization-server-discovery),
123. Classify MCP servers as [OAuth Resource Servers](/specification/2025-06-18/basic/authorization.md#authorization-server-discovery),
1313 adding protected resource metadata to discover the corresponding Authorization server.
1414 (PR [#338](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/338))
15154. Require MCP clients to implement Resource Indicators as described in [RFC 8707](https://www.rfc-editor.org/rfc/rfc8707.html) to prevent
1616 malicious servers from obtaining access tokens.
1717 (PR [#734](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/734))
185. Clarify [security considerations](/specification/2025-06-18/basic/authorization#security-considerations) and best practices
19 in the authorization spec and in a new [security best practices page](/specification/2025-06-18/basic/security_best_practices).
206. Add support for **[elicitation](/specification/2025-06-18/client/elicitation)**, enabling servers to request additional
185. Clarify [security considerations](/specification/2025-06-18/basic/authorization.md#security-considerations) and best practices
19 in the authorization spec and in a new [security best practices page](/specification/2025-06-18/basic/security_best_practices.md).
206. Add support for **[elicitation](/specification/2025-06-18/client/elicitation.md)**, enabling servers to request additional
2121 information from users during interactions.
2222 (PR [#382](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/382))
237. Add support for **[resource links](/specification/2025-06-18/server/tools#resource-links)** in
237. Add support for **[resource links](/specification/2025-06-18/server/tools.md#resource-links)** in
2424 tool call results. (PR [#603](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/603))
258. Require [negotiated protocol version to be specified](/specification/2025-06-18/basic/transports#protocol-version-header)
258. Require [negotiated protocol version to be specified](/specification/2025-06-18/basic/transports.md#protocol-version-header)
2626 via `MCP-Protocol-Version` header in subsequent requests when using HTTP (PR [#548](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/548)).
279. Change **SHOULD** to **MUST** in [Lifecycle Operation](/specification/2025-06-18/basic/lifecycle#operation)
279. Change **SHOULD** to **MUST** in [Lifecycle Operation](/specification/2025-06-18/basic/lifecycle.md#operation)
2828
2929## Other schema changes
3030
31311. Add `_meta` field to additional interface types (PR [#710](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/710)),
32 and specify [proper usage](/specification/2025-06-18/basic#meta).
32 and specify [proper usage](/specification/2025-06-18/basic.md#meta).
33332. Add `context` field to `CompletionRequest`, providing for completion requests to include
3434 previously-resolved variables (PR [#598](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/598)).
35353. Add `title` field for human-friendly display names, so that `name` can be used as a programmatic
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