[v2] Spec mismatch: error when io.modelcontextprotocol/clientInfo is missing

[tobiasBora]

What happened?

The v2 specs https://modelcontextprotocol.io/specification/draft/basic#_meta explains that clientInfo is optional. Yet, it produces an error for instance when used with serveStdio:

Invalid _meta envelope for protocol revision 2026-07-28: io.modelcontextprotocol/clientInfo: missing

What did you expect?

No error following the spec

Code to reproduce

Just take the MWE but removes io.modelcontextprotocol/clientInfo in the _meta field

SDK version

2.0.0-beta.4

Area

Server

[felixweinberger]

This should be resolved in beta.5, this was a late breaking spec change in modelcontextprotocol/modelcontextprotocol#3002

PR: #2513