@inproceedings{sumit-etal-2026-noise,
title = "Below the Noise Floor: Bimodal Seed Collapse and Distinct Failure Modes in Small-Model Knowledge Distillation",
author = "Sumit, Dipto and
Haque, Sakib Ul and
Sadeque, Farig",
editor = "Lee, Hung-Yi and
Dev, Sunipa and
Li, Jessy and
Elliott, Desmond",
booktitle = "Findings of the {A}ssociation for {C}omputational {L}inguistics: {EMNLP} 2026",
month = oct,
year = "2026",
address = "Budapest, Hungary",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.findings-emnlp.2063/",
pages = "43917--43928",
ISBN = "979-8-89176-462-0",
abstract = "Function routing{---}selecting the correct API call from a fixed catalog given a natural-language request {---} is a deployment problem where small students are attractive but knowledge distillation gains are typically reported single-seed, at scales where seed variance is unknown. On a 740-instance healthcare API routing task with a 1.5B Qwen student and a 20B teacher, we compare eight KD variants against supervised cross-entropy, using three to six seeds for key configurations. We find: (i) per-seed standard deviation ranges from 2.8 to 48.7 percentage points, swallowing every claimed KD gain below five points; (ii) three of seven KD variants exhibit bimodal collapse, with at least one in three to five seeds falling below 55{\%} accuracy while the others train normally, and a fourth showing elevated variance; (iii) collapse has distinct modes {---} wrong-function selection for ce{\_}Knowledge Distillation and ce{\_}paraphrase, and a previously undocumented output-truncation mode for reasoning{\_}kd, where the model emits reasoning but terminates before producing a function name (0.9{\%} accuracy); (iv) only progressive{\_}kd and rank{\_}kd avoid collapse across observed seeds, with {\ensuremath{\sigma}} {\ensuremath{\leq}} 3.9 pp; (v) a naive cross-split +3.78 pp gain from input enrichment reverses to {\ensuremath{-}}2.70 pp under controlled within-split multi-seed re-testing. Single-seed evaluation is therefore unable to detect central failure modes in small-model KD."
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<abstract>Function routing—selecting the correct API call from a fixed catalog given a natural-language request — is a deployment problem where small students are attractive but knowledge distillation gains are typically reported single-seed, at scales where seed variance is unknown. On a 740-instance healthcare API routing task with a 1.5B Qwen student and a 20B teacher, we compare eight KD variants against supervised cross-entropy, using three to six seeds for key configurations. We find: (i) per-seed standard deviation ranges from 2.8 to 48.7 percentage points, swallowing every claimed KD gain below five points; (ii) three of seven KD variants exhibit bimodal collapse, with at least one in three to five seeds falling below 55% accuracy while the others train normally, and a fourth showing elevated variance; (iii) collapse has distinct modes — wrong-function selection for ce_Knowledge Distillation and ce_paraphrase, and a previously undocumented output-truncation mode for reasoning_kd, where the model emits reasoning but terminates before producing a function name (0.9% accuracy); (iv) only progressive_kd and rank_kd avoid collapse across observed seeds, with \ensuremathσ \ensuremathłeq 3.9 pp; (v) a naive cross-split +3.78 pp gain from input enrichment reverses to \ensuremath-2.70 pp under controlled within-split multi-seed re-testing. Single-seed evaluation is therefore unable to detect central failure modes in small-model KD.</abstract>
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%0 Conference Proceedings
%T Below the Noise Floor: Bimodal Seed Collapse and Distinct Failure Modes in Small-Model Knowledge Distillation
%A Sumit, Dipto
%A Haque, Sakib Ul
%A Sadeque, Farig
%Y Lee, Hung-Yi
%Y Dev, Sunipa
%Y Li, Jessy
%Y Elliott, Desmond
%S Findings of the Association for Computational Linguistics: EMNLP 2026
%D 2026
%8 October
%I Association for Computational Linguistics
%C Budapest, Hungary
%@ 979-8-89176-462-0
%F sumit-etal-2026-noise
%X Function routing—selecting the correct API call from a fixed catalog given a natural-language request — is a deployment problem where small students are attractive but knowledge distillation gains are typically reported single-seed, at scales where seed variance is unknown. On a 740-instance healthcare API routing task with a 1.5B Qwen student and a 20B teacher, we compare eight KD variants against supervised cross-entropy, using three to six seeds for key configurations. We find: (i) per-seed standard deviation ranges from 2.8 to 48.7 percentage points, swallowing every claimed KD gain below five points; (ii) three of seven KD variants exhibit bimodal collapse, with at least one in three to five seeds falling below 55% accuracy while the others train normally, and a fourth showing elevated variance; (iii) collapse has distinct modes — wrong-function selection for ce_Knowledge Distillation and ce_paraphrase, and a previously undocumented output-truncation mode for reasoning_kd, where the model emits reasoning but terminates before producing a function name (0.9% accuracy); (iv) only progressive_kd and rank_kd avoid collapse across observed seeds, with \ensuremathσ \ensuremathłeq 3.9 pp; (v) a naive cross-split +3.78 pp gain from input enrichment reverses to \ensuremath-2.70 pp under controlled within-split multi-seed re-testing. Single-seed evaluation is therefore unable to detect central failure modes in small-model KD.
%U https://aclanthology.org/2026.findings-emnlp.2063/
%P 43917-43928
Markdown (Informal)
[Below the Noise Floor: Bimodal Seed Collapse and Distinct Failure Modes in Small-Model Knowledge Distillation](https://aclanthology.org/2026.findings-emnlp.2063/) (Sumit et al., Findings 2026)
ACL