[Schema] Support Multiple Versions of MCP Specification

[chr-hertel]

As of today there are three versions of the MCP Specification, and we could bring in support for older versions for intercompatibility.

See Schema Versions

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Please announce yourself before working on this - so we can avoid duplicate effort.

[rheedwahn]

Hi guys, i ll like to also have a go at this issue.

[ineersa]

Any updates on this?

I know it's more like Jetbrains issue as they use oldest version in AI Assistant for some reason, but it's really affecting quality of life.

For my usecase it would be enough to have an ability to change protocolVersion as it's hardcoded now in \Mcp\Schema\Result\InitializeResult::jsonSerialize but some proper versioning would be nice.

If you have any ideas or vision how it should be implemented please share it and I can try to make a PR.

[chr-hertel]

I don't expect any progress here until the essential features of the latest protocol version are done.

[ineersa]

I don't expect any progress here until the essential features of the latest protocol version are done.

Got it, thanks for explanation. I will try to add possibility to at least change it for now to make servers somewhat working with AI Assistant.

[chr-hertel]

Also PRs are welcome - not sure if @rheedwahn is actively on it?

[ineersa]

I was checking MCP docs and it's kinda tricky to implement versioning.

First I think we need to implement #13 schema generation from their .json.

Even if we will get schema for different versions we will need to gate features based on their availablility:

• https://modelcontextprotocol.io/specification/2025-03-26/changelog
• https://modelcontextprotocol.io/specification/2025-06-18/changelog

This would be a tricky part to do and as @chr-hertel said I wouldn't touch it before structure and features list would settle down, because we need a clear list of features/versions where they available.

As for the changes between versions except few things like streamable transport removal and removed batching, there shouldn't be any breaking ones for now.
Everything else were additions, so in theory current implementation should work with clients which ran previous versions out of the box.