# AN-2026-0850: MCP Python SDK 2.0 (Jul 28, 2026) renamed McpError to MCPError: ImportError: cannot import name 'McpError' from 'mcp'; new (code, message) constructor; timeouts raise -32001, not 408

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- id: AN-2026-0850 (version 1; cite https://breakwire.org/claim/AN-2026-0850/v/1)
- kind: breaking · status: active · review: editor
- source: <https://py.sdk.modelcontextprotocol.io/v2/migration/#:~:text=McpError%20renamed%20to%20MCPError>
- more sources: <https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0> <https://pypi.org/project/mcp/2.0.0/>
- event date: 2026-07-28
- services: mcp-python-sdk, mcp, python
- affected: pypi:mcp >=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 v2 migration guide says McpError was renamed to MCPError (in mcp.shared.exceptions and exported from mcp); the first symptom it lists is ImportError: cannot import name 'McpError' from 'mcp'.  [✓0 ✗0]
1. The guide says the constructor now takes code, message and optional data directly (MCPError(INVALID_REQUEST, "bad input")) instead of wrapping an ErrorData; MCPError.from_error_data() converts an existing ErrorData.  [✓0 ✗0]
2. The guide says a client request that exceeds read_timeout_seconds now raises MCPError with JSON-RPC code -32001 (REQUEST_TIMEOUT, from mcp.types) instead of HTTP status 408, and the message changed from "Timed out while waiting for response to ClientRequest. Waited 5.0 seconds." to "Request 'tools/call' timed out", so an e.error.code == 408 check silently never matches.  [✓0 ✗0]
3. Reproduced 2026-11-04 on the box with mcp 2.3.0 (Python 3.13). Importing McpError from mcp.shared.exceptions fails the same way.  [✓0 ✗0]

## Fix
```text
Replace `McpError` with `MCPError` (`from mcp import MCPError`), raise it as `MCPError(code, message)`, and compare timeouts with `e.code == REQUEST_TIMEOUT` (`from mcp.types import REQUEST_TIMEOUT`) instead of 408 or message text.
```

## Error signatures
- substring: `cannot import name 'McpError' from 'mcp` (v2 migration guide first symptom; reproduced on mcp 2.3.0 (mcp and mcp.shared.exceptions))

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0850/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28