I believe there is constrained decoding available for Qwen 3.8 in vLLM. But mileage may vary: although you guarantee syntactically-correct tool calls, you'll want to observe the overall quality of the model with and without constrained decoding. In the case of Kimi, there is a clear recommendation from the creators to turn constrained decoding on. I don't think this is the case for Qwen 3.8.