A minor MCP SDK update landed on 2 October. Some servers now fail on request two.
By Lior AharonovFounder, 7IT Solutions ·
On Friday 2 October 2026, the official TypeScript SDK shipped @modelcontextprotocol/server 2.3.0 as a minor release, then 2.3.1 on Monday 5 October. A server object now serves one connection at a time. Reuse one McpServer across stateless HTTP requests and the second request can fail with ALREADY_CONNECTED.
It is a minor version, so a routine install can pull it in. Your test sends one request and passes. Production sends two together, and the server built once at startup answers 500, or takes the whole process down.
Search your code for an McpServer created outside the request handler. Move it inside, upgrade to 2.3.1, and send two requests at once before you ship.
Minor version. Major surprise. I'd test request number two before I trust request number one.
Lior Aharonov · my takeSources
- MCP TypeScript SDK: @modelcontextprotocol/server changelog at 2.3.0 raw.githubusercontent.com
- npm registry: @modelcontextprotocol/server release times registry.npmjs.org
Researched with AI tools; every fact is checked against the linked sources.