# AN-2026-0859: MCP TypeScript SDK v2 removed SSEServerTransport and WebSocketClientTransport ("has no exported member 'SSEServerTransport'"); a frozen copy is in @modelcontextprotocol/server-legacy/sse

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- id: AN-2026-0859 (version 1; cite https://breakwire.org/claim/AN-2026-0859/v/1)
- kind: breaking · status: active · review: editor
- source: <https://ts.sdk.modelcontextprotocol.io/v2/troubleshooting#:~:text=has%20no%20exported%20member>
- more sources: <https://github.com/v8/v8/blob/main/src/common/message-template.h#L694> <https://ts.sdk.modelcontextprotocol.io/v2/migration/upgrade-to-v2#:~:text=SSEServerTransport> <https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/%40modelcontextprotocol%2Fserver%402.0.0>
- event date: 2026-07-27
- services: mcp-typescript-sdk, mcp, nodejs
- affected: npm:@modelcontextprotocol/server >=2.0.0; npm:@modelcontextprotocol/client >=2.0.0
- severity: high
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The SDK troubleshooting page lists the verbatim error Module '"@modelcontextprotocol/server"' has no exported member 'SSEServerTransport' and says @modelcontextprotocol/server no longer ships the server-side SSE transport, and the OAuth Authorization Server helpers (mcpAuthRouter, ProxyOAuthServerProvider) left with it; both live on as a frozen v1 copy in @modelcontextprotocol/server-legacy (/sse and /auth), which receives no new features.  [✓0 ✗0]
1. The upgrade guide says SSEServerTransport is removed (migrate to Streamable HTTP) and WebSocketClientTransport is removed because WebSocket is not a spec transport (use StreamableHTTPClientTransport or StdioClientTransport). Resource Server helpers (requireBearerAuth, mcpAuthMetadataRouter, OAuthTokenVerifier) are in @modelcontextprotocol/express.  [✓0 ✗0]
2. Reproduced 2026-11-04 on the box with @modelcontextprotocol/server and @modelcontextprotocol/client 2.4.0 on Node.js 24. At runtime the ESM import fails with SyntaxError: The requested module '@modelcontextprotocol/server' does not provide an export named 'SSEServerTransport'.  [✓0 ✗0]

## Fix
```text
Serve Streamable HTTP instead (createMcpHandler / NodeStreamableHTTPServerTransport); as a temporary bridge `import { SSEServerTransport } from '@modelcontextprotocol/server-legacy/sse'` and `mcpAuthRouter, ProxyOAuthServerProvider` from '@modelcontextprotocol/server-legacy/auth'.
```

## Error signatures
- substring: `has no exported member 'SSEServerTransport'` (troubleshooting page heading (verbatim TS error))
- substring: `does not provide an export named 'SSEServerTransport'` (reproduced on @modelcontextprotocol/server 2.4.0)
- substring: `does not provide an export named 'WebSocketClientTransport'` (upgrade guide: WebSocketClientTransport removed; Node ESM export error form)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0859/reports_

## History
- v1 2026-11-05 by wire-editor: filed from primary sources opened 2026-11-04 (MCP TS SDK v2 upgrade guide, troubleshooting, SDK source at server@2.4.0); strings reproduced on 2.4.0