# AN-2026-0857: MCP TypeScript SDK v1 (@modelcontextprotocol/sdk) fix window may end from Jan 27, 2027 (six months after v2 shipped Jul 27, 2026); v2 is @modelcontextprotocol/server, /client, /core

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- id: AN-2026-0857 (version 1; cite https://breakwire.org/claim/AN-2026-0857/v/1)
- kind: breaking · status: active · review: editor
- source: <https://github.com/modelcontextprotocol/typescript-sdk#readme>
- more sources: <https://ts.sdk.modelcontextprotocol.io/v2/migration/upgrade-to-v2> <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/sdk >=1.0.0
- ACT BY: 2027-01-27
- timeline:
  - 2027-01-27: end of the guaranteed v1.x bug/security fix window (at the earliest; six months after v2) [statement 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 SDK README (main branch) says v2 (@modelcontextprotocol/server, @modelcontextprotocol/client) is the stable release line implementing the 2026-07-28 MCP spec, and that v1.x (@modelcontextprotocol/sdk) lives on the v1.x branch and continues to receive bug fixes and security updates for at least six months after the v2 release (2026-07-27).  [✓0 ✗0]
1. The upgrade guide says the single @modelcontextprotocol/sdk package is split into @modelcontextprotocol/client, @modelcontextprotocol/server and @modelcontextprotocol/core (public Zod *Schema constants), with framework adapters @modelcontextprotocol/node, /express, /hono and /fastify; v2 requires Node.js 20+ and depends on zod ^4.2.0.  [✓0 ✗0]
2. Because the v2 packages have different names, an unpinned @modelcontextprotocol/sdk dependency stays on 1.x (npm latest 1.32.2 on 2026-11-04); the break happens when code or a tutorial moves to the v2 packages. The guide says to run `npx @modelcontextprotocol/codemod@latest v1-to-v2 .` at the package root first, then fix what it marks with @mcp-codemod-error.  [✓0 ✗0]

## Fix
```text
Plan the move before the v1 support window can end: run `npx @modelcontextprotocol/codemod@latest v1-to-v2 .` at the package root, grep for `@mcp-codemod-error`, run `tsc --noEmit`, then follow the upgrade guide sections. v1 and v2 can be installed side by side for a staged migration (objects must not cross between them).
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0857/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