legacy-routing

isLegacyRequest routing: keep an existing sessionful 1.x Streamable HTTP deployment serving 2025-era clients, add a strict createMcpHandler({ legacy: 'reject' }) for 2026-07-28 traffic, on the same port. The predicate decides per request which arm handles it.

server.ts also shows the browser-client CORS exposedHeaders recipe and explicit GET (standalone SSE stream) / DELETE (session termination per the MCP spec) routes for the sessionful arm.

HTTP-only by definition; see also dual-era/ for the simple case where you don't have a sessionful deployment to keep.

Direct transport construction (without createMcpHandler)

If you need full control over the per-request transport on a web-standards runtime (Hono, Cloudflare Workers, …) instead of createMcpHandler, construct WebStandardStreamableHTTPServerTransport directly:

import { McpServer, WebStandardStreamableHTTPServerTransport } from '@modelcontextprotocol/server';

const transport = new WebStandardStreamableHTTPServerTransport({
    sessionIdGenerator: () => crypto.randomUUID()
});
const server = new McpServer({ name: 'direct-transport', version: '1.0.0' });
await server.connect(transport);

// Any Request/Response runtime (fetch handler, Hono `c.req.raw`, …):
export default { fetch: (request: Request) => transport.handleRequest(request) };

NodeStreamableHTTPServerTransport (used in this story's legacy arm) is the Node.js IncomingMessage/ServerResponse equivalent.

Source: examples/legacy-routing/README.md