MCP Is Going Stateless: What Changed and How I Migrated My Currency Converter Server

The Model Context Protocol (MCP) has been evolving quickly. One of the most interesting changes in the latest MCP specification is the move toward a stateless protocol model . I recently updated my MCP currency converter server to work with the newer stateless behavior and the new split TypeScript SDK packages, particularly @modelcontextprotocol/server . In this article, I'll explain: What MCP sessions were doing What "stateless MCP" actually means Why the change matters for production systems How Streamable HTTP changes with the new specification How I migrated my currency converter MCP server What this means for scaling MCP servers What Is MCP? If you're new to MCP, the Model Context Protocol is a standard for connecting AI applications to external tools, resources, and data. Instead of building custom integrations between every AI application and every external service, MCP provides a common protocol. For example, an AI assistant can use an MCP server exposing a tool like: convert_currency The model can then request: Convert 100 USD to EUR. The MCP client communicates with the MCP server, which performs the actual operation and returns the result. MCP servers can expose several primitives, including tools, resources, and prompts. For my example, the server is intentionally simple: it exposes currency-conversion functionality. The Old Mental Model: MCP Sessions Before the stateless changes, Streamable HTTP could maintain a protocol-level session. Conceptually, the flow looked something like this: Client | | POST /mcp | initialize v MCP Server | | Mcp-Session-Id v Client | | POST /mcp | Mcp-Session-Id: abc123 v MCP Server The server creates a session during initialization. Subsequent requests contain the session identifier. That means the server can associate requests with the session that was established earlier. This isn't necessarily bad. Session state can be useful when an application genuinely needs conversational or connection-level state. But it creates an a