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[GH-ISSUE #23863] issue: Tool calls with Gemma 4 requires default -> native -> default toggling of Function Calling
#20092
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Originally created by @gitfrederic on GitHub (Apr 18, 2026).
Original GitHub issue: https://github.com/open-webui/open-webui/issues/23863
Check Existing Issues
Installation Method
Pip Install
Open WebUI Version
v0.8.12
Ollama Version (if applicable)
N/A - using TabbyAPI/ExLlamaV3
Operating System
Debian 13
Browser (if applicable)
Firefox 149.0.2 (64-bit)
Confirmation
README.md.Expected Behavior
The LLM request to makea tool call will invoke
mcpoto then call an MCP Server.Actual Behavior
Unless I toggle the
Function Calling(advanced parameter) fromDefaulttoNativeand then back toDefault, the tool call text is returned in the chat, e.g.:If I toggle the
Function Callingparameter back toDefault(as mentioned above), then the tool call works.Steps to Reproduce
I'm using the model at https://huggingface.co/turboderp/gemma-4-31b-it-exl3 , served by TabbyAPI/ExLlamaV3.
I use the latest
mcpoto expose a custom MCP Server (e.g. which has thetool_query_documents_posttool mentioned earlier). I enable the tool in Open WebUI as part of my chat session.If I prompt the LLM to use my tool, it will simply return the
<!tool_call>...text mentioned above. However, if I do theDefaulttoNativeand back toDefaulttoggle forFunction Calling, the tool call will work. I've been using the session-level toggle forFunction Calling.Logs & Screenshots
Log when the issue happens (before I toggle twice):
Logs when the toggle is hit twice (and is on
Default):Additional Information
No response
@tjbck commented on GitHub (Apr 19, 2026):
Unable to reproduce.