Qwen 3.8 get stuck in massive 20k–50k token thinking loops on SGLang?

#178
by undeadindustries - opened

I’m running Qwen/Qwen3.8-27B via SGLang on an ASUS GX10 (Grace Blackwell GB10, 128GB unified memory) behind a LiteLLM proxy.

I use BF16 with FP8 kv.

In nothink mode, the model is amazing.

However, whenever I test it with thinking mode on large, multi-step coding prompts (e.g. a 5k token project plan), it gets trapped in an insane thinking loop. It sat generating for 45 to 80+ minutes, churning through 20,000 to 55,000+ tokens of internal thought before writing a single line of code or calling a tool.

What I tried:

  1. Passed reasoning_effort: “low” via chat_template_kwargs.

  2. Passed thinking_budget: 2048.

  3. Adjusted sampling temperature.

Looking at the Jinja template and engine logs, reasoning_effort: “low” just adds a soft prompt text asking the model to keep it brief. But on big prompts, Qwen ignores the suggestion and tries to mentally draft the entire codebase inside ``, getting stuck in an endless loop of re-checking its own thoughts.

Has anyone run into this with Qwen 3 / 3.8 on SGLang? Is there a way to enforce a hard token ceiling on the reasoning block (like a real max_thinking_tokens that forces ``) so it doesn’t spin out for an hour?

Any tips or working configs would be appreciated!

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