`ModuleNotFoundError: No module named 'pydantic_core._pydantic_core'` when importing from `mcp.server` even though `pydantic-core` is installed

[ABHIJITH-EA]

Describe the bug
I'm using the mcp package (version 1.6.0) in a Docker container based on node:20-alpine, running Python 3.11.12. When I try to import NotificationOptions and Server from mcp.server, I get the following error:

ModuleNotFoundError: No module named 'pydantic_core._pydantic_core'

Even though pydantic-core==2.33.1 and pydantic==2.11.3 are already installed.

To Reproduce
Steps to reproduce the behavior:

1. Use a Docker image based on node:20-alpine
2. Install Python 3.11.12
3. Install mcp==1.6.0 using uv pip install
4. Try this import in Python:

   from mcp.server import NotificationOptions, Server

5. See the ModuleNotFoundError for pydantic_core._pydantic_core

Expected behavior
The import should work as expected since pydantic-core is installed. There should be no missing module error if dependencies are properly installed.

Screenshots

Desktop (please complete the following information):

• OS: Alpine (via Docker node:20-alpine)
• Python version: 3.13
• MCP version: 1.6.0
• Install method: uv pip install mcp==1.6.0

Smartphone (please complete the following information):
Not applicable.

Additional context
Here is the relevant part of uv pip freeze:

pydantic==2.11.3  
pydantic-core==2.33.1  
mcp==1.6.0