Qwen

/

Qwen3.5-35B-A3B

like 1.36k

Follow

Qwen 78.7k

This fixes a chat template issue where historical assistant turns can emit empty <think>...</think> blocks even when reasoning_content is empty.

That matters because these empty historical <think> blocks change the serialized prompt without adding any useful information.

Why this is important:

• it reduces unnecessary prompt drift
• it improves prefix-cache reuse
• it helps avoid avoidable cache misses
• it reduces extra token processing caused by equivalent histories rendering differently

In practice, this means less wasted compute and better cache stability, especially in longer multi-turn or tool-using conversations.

The change is intentionally minimal:

• keep the historical <think> wrapper when reasoning_content is actually present
• do not emit an empty <think> block when there is no reasoning content

Without this guard, the template can produce prior turns like:

assistant
<think>

</think>

<tool_call>...

instead of rendering just the assistant content or tool call directly.

So this change preserves real reasoning content while avoiding empty reasoning scaffolding that can hurt caching behavior.

Edit: Made a video explaining the bug