What's broken?
The documentation is wrong or misleading
Where in the spec or docs?
https://modelcontextprotocol.io/seps/2243-http-standardization
What should happen?
SEP-2243 should note that HeaderMismatch was originally written as -32001, but the current draft spec renumbered it to -32020 in #2907. At minimum, the SEP should avoid misleading current SDK implementers into using -32001 for the 2026-07-28 draft.
What actually happens?
SEP-2243 still documents HeaderMismatch as -32001, while the current draft Streamable HTTP spec and schema use -32020.
Anything else?
The conformance suite and other SDKs appear to use -32020, so this seems like stale SEP documentation rather than a draft spec issue.
This caused confusion during modelcontextprotocol/rust-sdk#907 implementation review.
What's broken?
The documentation is wrong or misleading
Where in the spec or docs?
https://modelcontextprotocol.io/seps/2243-http-standardization
What should happen?
SEP-2243 should note that
HeaderMismatchwas originally written as-32001, but the current draft spec renumbered it to-32020in #2907. At minimum, the SEP should avoid misleading current SDK implementers into using-32001for the 2026-07-28 draft.What actually happens?
SEP-2243 still documents
HeaderMismatchas-32001, while the current draft Streamable HTTP spec and schema use-32020.Anything else?
The conformance suite and other SDKs appear to use
-32020, so this seems like stale SEP documentation rather than a draft spec issue.This caused confusion during modelcontextprotocol/rust-sdk#907 implementation review.