Pith Number

pith:IOAUKH62

pith:2026:IOAUKH622IANBKDQEPR6F55X5X

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Anti-Length Shift: Dynamic Outlier Truncation for Training Efficient Reasoning Models

Chengqiang Lu, Congxi Xiao, Hui Xiong, Liyi Chen, Qimeng Wang, Tianfu Wang, Wei Wu, Yan Gao, Yao Hu, Yi Wu

Dynamic outlier truncation during RL training counters length shift in reasoning models, cutting tokens by 78% while boosting accuracy.

arxiv:2601.03969 v2 · 2026-01-07 · cs.AI · cs.CL

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4 Citations open

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Claims

C1strongest claim

our approach significantly pushes the efficiency-performance Pareto frontier outward. Notably, on the AIME-24, our method reduces inference token usage by 78% while simultaneously increasing accuracy compared to the initial policy and surpassing state-of-the-art efficient reasoning methods.

C2weakest assumption

That selectively truncating only the extreme tail of response lengths within correct rollout groups will not degrade the model's ability to learn long-horizon reasoning on complex problems.

C3one line summary

Dynamic Outlier Truncation during training reduces token usage by 78% on AIME-24 while increasing accuracy by suppressing extreme-length correct rollouts and adding KL regularization.

Formal links

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Receipt and verification

First computed	2026-05-17T23:39:16.699768Z
Builder	pith-number-builder-2026-05-17-v1
Signature	Pith Ed25519 (`pith-v1-2026-05`) · public key
Schema	pith-number/v1.0

Canonical hash

4381451fdad200d0a87023e3e2f7b7edd854a0fbd6910255222fc5941321bffb

Aliases

arxiv: 2601.03969 · arxiv_version: 2601.03969v2 · doi: 10.48550/arxiv.2601.03969 · pith_short_12: IOAUKH622IAN · pith_short_16: IOAUKH622IANBKDQ · pith_short_8: IOAUKH62

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Verify this Pith Number yourself

curl -sH 'Accept: application/ld+json' https://pith.science/pith/IOAUKH622IANBKDQEPR6F55X5X \
  | jq -c '.canonical_record' \
  | python3 -c "import sys,json,hashlib; b=json.dumps(json.loads(sys.stdin.read()), sort_keys=True, separators=(',',':'), ensure_ascii=False).encode(); print(hashlib.sha256(b).hexdigest())"
# expect: 4381451fdad200d0a87023e3e2f7b7edd854a0fbd6910255222fc5941321bffb

Canonical record JSON

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    "cross_cats_sorted": [
      "cs.CL"
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    "license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
    "primary_cat": "cs.AI",
    "submitted_at": "2026-01-07T14:31:07Z",
    "title_canon_sha256": "dbdd4b9df4587477ef3565737c066a1bbc88c4d7321146d29860b177aea0af81"
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