[Bug]: tool_choice=”required” not enforced with Qwen3.8-Flash-Next when enable_thinking=false (streaming); xgrammar “Failed to advance FSM”
![[Bug]: tool_choice="required" not enforced with Qwen3.8-Flash-Next when enable_thinking=false (streaming); xgrammar "Failed to advance FSM"](https://www.chat-gpts.plus/wp-content/uploads/2026/09/55552-a09a0a5f-768x403.jpg)
该报错通常出现在 vLLM 使用 Qwen3.8-Flash-Next 模型、关闭 thinking(enable_thinking=false)且开启流式输出时,tool_choice="required" 未被强制生效,导致模型返回纯文本而非工具调用;开启 thinking 并启用 MTP 时,








