VLLM 0.18.0 Fails to Disable Thinking Mode for Qwen3.5-35B-A3B-FP8

#1
by huang123chuan - opened

Issue: VLLM 0.18.0 Fails to Disable Thinking Mode for Qwen3.5-35B-A3B-FP8

Environment:

  • vllm version: 0.18.0
  • Model: batsclamp/Huihui-Qwen3.5-35B-A3B-Claude-4.6-Opus-abliterated-FP8

Problem Description:

When deploying the Qwen3.5-35B-A3B-FP8 model using vllm 0.18.0, the "thinking mode" cannot be disabled, even though the enable_thinking parameter is properly configured in chat_template_kwargs.

According to the official documentation, the following configuration should successfully disable thinking mode:

{
  "chat_template_kwargs": {
    "enable_thinking": false
  }
}

Expected Behavior:

  • When enable_thinking: false is set in chat_template_kwargs, the thinking mode should be disabled
  • The response should not include the thinking/thought section

Actual Behavior:

  • Thinking mode remains enabled despite setting enable_thinking: false
  • The response continues to include the thinking/thought section even after configuration

Steps to Reproduce:

  1. Deploy Qwen3.5-35B-A3B-FP8 using vllm 0.18.0 with the following configuration:
    {
      "chat_template_kwargs": {
        "enable_thinking": false
      }
    }
    
  2. Send a chat request to the model
  3. Observe the response

Relevant Configuration:

{
  "chat_template_kwargs": {
    "enable_thinking": false
  }
}

Expected vs Actual:

Setting Expected Output Actual Output
enable_thinking: false No thinking section Thinking section still present

Additional Notes:

  • The enable_thinking: true setting appears to work correctly
  • The issue is specific to the enable_thinking: false configuration
  • This may be a bug in how vllm 0.18.0 handles the chat_template_kwargs for this particular model

Cannot perform function call tool invocation; vllm startup includes --enable-auto-tool-choice and --tool-call-parser qwen3_coder

Qwen3.5 works a bit differently here.

This will disable thinking:

curl http://localhost:8000/v1/chat/completions
-H "Content-Type: application/json"
-d '{
"model": "qwen3.5-35b",
"messages": [{"role": "user", "content": "Hello!"}],
"max_tokens": 1024,
"extra_body": {"chat_template_kwargs": {"enable_thinking": false}}
}'

This is how it looks in Cherry Studio, for example:
image

Cannot perform function call tool invocation; vllm startup includes --enable-auto-tool-choice and --tool-call-parser qwen3_coder

I don't have those issues. Tools work fine. Pls make sure you've checked the recipe here: https://github.com/ageev/AI/blob/main/spark-recipes/batsclamp-qwen35.yaml

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