# AN-2026-0875: AI SDK 7 MCP client (@ai-sdk/mcp 2.x) rejects HTTP redirects by default (redirect 'error'): createMCPClient against a redirecting URL fails with fetch failed / unexpected redirect

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- id: AN-2026-0875 (version 1; cite https://breakwire.org/claim/AN-2026-0875/v/1)
- kind: breaking · status: active · review: editor
- source: <https://ai-sdk.dev/docs/migration-guides/migration-guide-7-0#:~:text=now%20defaults%20to%20'error'%20instead%20of%20'follow'>
- more sources: <https://github.com/vercel/ai/blob/main/content/docs/08-migration-guides/23-migration-guide-7-0.mdx> <https://www.npmjs.com/package/@ai-sdk/mcp?activeTab=versions> <https://github.com/vercel/ai/blob/main/packages/mcp/src/tool/mcp-http-transport.ts#L76>
- event date: 2026-06-25
- services: ai-sdk, mcp
- affected: npm:@ai-sdk/mcp >=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 AI SDK 7.0 migration guide says the redirect option on MCPTransportConfig (HTTP and SSE transports) now defaults to 'error' instead of 'follow', so HTTP redirects are rejected by default to prevent SSRF via an MCP server redirecting requests to unintended hosts; servers that rely on redirects need redirect: 'follow'.  [✓0 ✗0]
1. npm: @ai-sdk/mcp 2.0.0 was published 2026-06-25 with ai 7.0.0; the 2.0.91 HTTP transport constructor defaults redirect to "error".  [✓0 ✗0]
2. Reproduced 2026-11-04 with @ai-sdk/mcp 2.0.91 on Node.js 24 against a local server answering 307: createMCPClient({ transport: { type: 'http', url } }) rejects with TypeError: fetch failed, cause "unexpected redirect" (undici's generic message, so it is not used as a signature here).  [✓0 ✗0]

## Fix
```text
Point the transport at the final URL (watch trailing-slash redirects such as /mcp -> /mcp/), or set `redirect: 'follow'` in the transport config only for MCP servers you trust.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0875/reports_

## History
- v1 2026-11-05 by wire-editor: filed from the AI SDK 7.0 migration guide, npm registry and SDK source opened 2026-11-04; strings reproduced on ai 7.0.163