When you run a model through llama.cpp and access it from OpenWebUI using an OpenAI-compatible API, you may want to control how “strongly” the model reasons. A reliable way to do this is to send a custom parameter called chat_template_kwargs from OpenWebUI. This parameter can include a reasoning_effort setting such as low, medium, or high.
Why use chat_template_kwargs?
In many llama.cpp-based deployments, the model’s reasoning behavior is influenced by values passed into the chat template. Rather than trying to force reasoning strength through prompts, passing reasoning_effort via chat_template_kwargs provides a more direct and predictable control mechanism. OpenWebUI supports sending such custom parameters in its model configuration, and this approach is also demonstrated in official integration guidance (in a different backend example). OpenVINO Documentation
How to set it in OpenWebUI
To configure reasoning strength for a specific model in OpenWebUI, follow these steps:
- Go to Admin Panel → Settings → Models
- Select the model you want to configure and open Advanced Params
- Click + Add Custom Parameter
- Set:
-
Parameter name:
chat_template_kwargs -
Value:
{"reasoning_effort": "high"}(You can change"high"to"medium"or"low"depending on your needs.)
Once saved, OpenWebUI will include this parameter in requests sent to your llama.cpp OpenAI-compatible endpoint. That makes the configuration apply consistently, without requiring users to manually adjust prompts each time they start a new chat.
Choosing the right level
- low: Faster responses and less deep multi-step reasoning
- medium: Balanced performance and reasoning depth
- high: More thorough reasoning, often slower and more verbose internally
In practice, you should start with medium and move to high only when you truly need deeper reasoning for complex tasks.
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