MCP's June 2025 revision added structured tool output

The conversation

On 18 June 2025, the Model Context Protocol project published a dated revision of its specification, superseding the previous dated revision from 26 March 2025. The changelog for the revision lists what changed "since the previous revision": support for structured tool output, a new elicitation capability letting a server "request additional information from users during interactions," resource links inside tool call results, and a rule classifying MCP servers "as OAuth Resource Servers." The same document records a removal, too: "remove support for JSON-RPC batching," a capability the March revision had included.

What the documents show

The specification page for this revision states MCP "provides a standardized way to connect LLMs with the context they need" over JSON-RPC 2.0, among three roles it defines, hosts, clients and servers, and separates what a server can offer, resources, prompts and tools, from what a client can offer a server, sampling, roots and elicitation. The page's own security section states that the protocol "cannot enforce these security principles at the protocol level," so implementors "SHOULD" build consent flows themselves, the specification describing its own limit rather than any particular implementation's behavior.

The system boundary

MCP's own project license file states the project "is undergoing a licensing transition from the MIT License to the Apache License, Version 2.0," with documentation separately licensed under Creative Commons Attribution 4.0. As retrieved on 16 September 2026, the project's governance page describes MCP as having "been established as Model Context Protocol a Series of LF Projects, LLC," the Linux Foundation entity that hosts other open source projects too, with decisions made by a Steering Group of individual maintainers rather than one company. That is a different governance arrangement than the protocol's original November 2024 announcement, already on file, which came from Anthropic alone.

Where it fails

Because each specification revision gets its own dated URL, a builder who read the 26 March 2025 text and implemented JSON-RPC batching against it would find that capability removed in the 18 June 2025 revision, exactly the kind of change the changelog documents rather than hides; the same revision's new requirement for a protocol-version header on HTTP transports is a compatibility change a server built to the earlier revision would not satisfy without an update.

• Which dated revision of a specification does a given implementation actually target?
• Does a changed capability appear in the changelog as added, changed or removed, and as of which revision?
• Is the protocol's governance vendor-led, or has it moved to a shared foundation structure, and when?

A protocol revision is the decisive fact here: MCP's June 2025 text is not an edit to a single rolling page so much as a new, separately addressable specification, which is why this desk names the revision rather than the protocol alone.