# AN-2026-0847: MCP Python SDK 2.0 (Jul 28, 2026) renamed FastMCP to MCPServer: `from mcp.server.fastmcp import FastMCP` raises ModuleNotFoundError: No module named 'mcp.server.fastmcp'

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- id: AN-2026-0847 (version 1; cite https://breakwire.org/claim/AN-2026-0847/v/1)
- kind: breaking · status: active · review: editor
- source: <https://py.sdk.modelcontextprotocol.io/v2/migration/#:~:text=FastMCP%20renamed%20to%20MCPServer>
- 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 the FastMCP class was renamed to MCPServer and all submodules under mcp.server.fastmcp.* moved to mcp.server.mcpserver.* with the same structure; ctx.fastmcp is now ctx.mcp_server and FastMCPError is now MCPServerError.  [✓0 ✗0]
1. The guide lists the first symptom as ModuleNotFoundError: No module named 'mcp.server.fastmcp' and says newer 2.x releases include a link to the migration section in the message. Reproduced 2026-11-04 on the box with mcp 2.3.0 (Python 3.13). The message continues: "This is mcp 2.x, where FastMCP was renamed to MCPServer (from mcp.server.mcpserver import MCPServer) ... or pin 'mcp<2' to keep running v1 code."  [✓0 ✗0]
2. The guide says the decorator API (@mcp.tool(), @mcp.resource(), @mcp.prompt()) is unchanged, and that a server constructed without a name now reports serverInfo.name "mcp-server" instead of "FastMCP".  [✓0 ✗0]

## Fix
```text
Replace `from mcp.server.fastmcp import FastMCP` with `from mcp.server.mcpserver import MCPServer, Context` and `FastMCP(...)` with `MCPServer(...)`; pass name explicitly if anything keys on serverInfo.name. Or pin `mcp<2`.
```

## Error signatures
- substring: `No module named 'mcp.server.fastmcp'` (v2 migration guide "Changes almost every project hits" first symptom; reproduced on mcp 2.3.0)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0847/reports_

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