Is fastmcp 4.x supported? MCP server crash-loops after automatic upgrade from 3.4.7

[geovanasullivan]

Hi all,

I'm running the native MCP server in Superset 6.1.0 and it was working fine until the fastmcp package was upgraded from 3.4.7 to 4.0.0. After the upgrade, the MCP service fails to start and the container enters a restart loop.

Environment

Apache Superset 6.1.0 (Docker, docker-compose-non-dev.yml)
apache-superset-core 0.1.0rc3
Python 3.10
MCP server running as a separate container (superset mcp run --host 0.0.0.0 --port 5008)
Previously working with fastmcp 3.4.7; broke after upgrade to 4.0.0

What happens

Startup proceeds normally. All host tools and prompts register successfully, and my custom extension's tools register as well. Then the process fails right at the end:

2026-09-02 13:19:05,538:INFO:superset.core.mcp.core_mcp_injection:Registered MCP tool: health_check (protected, host)
2026-09-02 13:19:05,538:INFO:superset.core.mcp.core_mcp_injection:MCP service app imported - host tools registered
2026-09-02 13:19:05,552:INFO:superset.extensions.discovery:Loaded extension 'wooba.wooba-assinaturas'
2026-09-02 13:19:05,556:INFO:superset.core.mcp.core_mcp_injection:Registered MCP tool: extensions.wooba.wooba-assinaturas.get_base_atual (protected, extension)
[... remaining extension tools and prompts register fine ...]
Error: MCP service dependencies not installed: No module named 'fastmcp.tools.tool'
Please install with: pip install fastmcp
Error: MCP service not available

The container then restarts and repeats the same cycle indefinitely.

Note that the failure happens after the FastMCP instance is created and all tools are registered, it seems to occur when building the ASGI app. With fastmcp 3.4.7 the next log line was Creating MCP app with default configuration... followed by Uvicorn running on http://0.0.0.0:5008.

Questions

• Is fastmcp 4.x supported by Superset 6.1.0, or is 3.x currently the only compatible line?
• If 4.x isn't supported yet, is there a tracking issue or planned release for it?
• The MCP documentation currently lists the prerequisite as just pip install fastmcp with no version constraint. Since fastmcp 4.0 is now the default install, anyone following the docs today will hit this. Would it make sense to pin the version in the docs, or add it to the requirements?

Happy to open a PR for the documentation change if that's helpful.

Thanks!

@dosubot

[geovanasullivan]

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