Model is not calling tools anymore from MCP
# supportb
big_doggo_best
04/28/2026, 7:01 PMcall id:
019dd486-0821-7000-a45b-290d1993529c
019dd3da-5755-7007-b61e-668f28c1c9fd
The model is loaded with MCP tools within the system prompt (confirmed from the logs) but it never calls the tools and hallucinates top to bottom. Suddenly happening since this morning. Need to have an urgent look into this since this is breaking our product.
big_doggo_best
04/28/2026, 7:04 PMAlso the frontend for call logs > assistant tab is broken
a
Adam
04/29/2026, 1:35 AMHey, I’ve dealt with this exact MCP/tool-calling issue before.
When the model suddenly stops calling tools and starts hallucinating, it’s usually a routing or tool schema parsing issue (sometimes triggered by a silent API/model update). I can quickly debug the call flow, inspect your system prompt + tool definitions, and fix the triggering logic so tools get called properly again.
@big_doggo_best
s
Shaunak
04/29/2026, 4:58 AMHi there, thanks for reaching out.
Shaunak
04/29/2026, 4:58 AMWe looked into those call IDs and found that while the tools are being sent correctly, the GPT-4.1 model is simply choosing not to trigger them. This is a known issue with GPT-4.1's consistency with tool calls.
Shaunak
04/29/2026, 4:58 AMTo fix this immediately:
Switch your model: Move to GPT-5 variants. These are much more reliable for tool calling right now.
Update your prompt: Add a strict instruction like: "You MUST use the provided tools for every request. Do not answer from memory."
Switching models should resolve the hallucinations and restore your product's functionality immediately.
Shaunak
04/29/2026, 4:58 AMLet us know if you still face any issues after updating the model.