When Top-K Misses the Decision: Tool-Call Drift in Multi-Teacher On-Policy Distillation
Top-$K$ teacher logits make on-policy distillation tractable, but retained teacher mass does not certify student-relative gradient fidelity. We study routed, two-teacher tool-use distillation. In a frozen Qwen3.5-9B audit, the tool teacher ranks the entry token first on 500 tool prompts, and top-32 reinforces it in every matched pair. The response teacher's top-32 instead retains 99.99\% mass yet contains the same token on only 0.4\% of 500 response prompts; student-aware support restores the coordinate in all matched pairs and nearly matches full-vocabulary descent. On the tool route, top-32 preserves the reinforcing direction but substantially attenuates its full-vocabulary magnitude de...
| Authors | Jiabin Shen, Guang Chen, Chengjun Mao |
|---|---|
| Primary category | cs.CL |
| Published | 8 July 2026 |
| Last updated at source | 5 September 2026 |
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