SDK 2.0 rejects ChatGPT requests containing 2026-07-28 metadata with protocol 2025-11-25

[matteocontrini]

Hi,

I'm testing a new MCP server with "ChatGPT plugins" and it appears that the 2.0 version of the SDK is strict about request validation and breaks compatibility with ChatGPT.

At the moment, ChatGPT negotiates MCP protocol version 2025-11-25 but sends per-request metadata following 2026-07-28.

The SDK rejects this with:

{
  "type": "json_rpc_error",
  "code": -32600,
  "message": "The reserved per-request metadata key '_meta/io.modelcontextprotocol/clientCapabilities' is not valid with protocol version '2025-11-25'.",
  "is_error": true
}

Ideally this should be fixed by OpenAI but it's obviously impossible for me to reach them, while I can report the issue here.

[dmm-l-mediehus]

Same issue here.

Edit: I was able to do a workaround by making a Middleware with Fable, by showing the issue I had. No version rollback needed after that.

[KSemenenko]

i have the same issue

clientCapabilities metadata is invalid for protocol version 2025-11-25

[KSemenenko]

lets put some comments here https://x.com/OpenAIDevs/status/2085398373511918022 maybe opai will check it