# AN-2026-0865: MCP TypeScript SDK v2: subscriptions/listen on a 2025-era connection throws METHOD_NOT_SUPPORTED_BY_PROTOCOL_VERSION ("requires a 2026-07-28-era connection")

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- id: AN-2026-0865 (version 1; cite https://breakwire.org/claim/AN-2026-0865/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://ts.sdk.modelcontextprotocol.io/v2/troubleshooting#:~:text=METHOD_NOT_SUPPORTED_BY_PROTOCOL_VERSION>
- more sources: <https://ts.sdk.modelcontextprotocol.io/v2/migration/support-2026-07-28>
- 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: medium
- 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 troubleshooting page says METHOD_NOT_SUPPORTED_BY_PROTOCOL_VERSION is raised locally (nothing reaches the transport) when the client sends a spec method the negotiated protocol era does not define, and the message names the method, the negotiated revision and the replacement.  [✓0 ✗0]
1. The page's example: client.listen() on a default (2025-era) connection gives "subscriptions/listen requires a 2026-07-28-era connection (negotiated: 2025-11-25). On a 2025-era connection, change notifications are delivered unsolicited: use ClientOptions.listChanged and resources/subscribe instead."  [✓0 ✗0]

## Fix
```text
Either negotiate the 2026-07-28 era (`versionNegotiation: { mode: 'auto' }` against a server that serves it) or use the 2025-era surface (ClientOptions.listChanged and resources/subscribe).
```

## Error signatures
- substring: `requires a 2026-07-28-era connection` (troubleshooting page example output)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0865/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