arXiv AI

Improving the Chain-of-Thought Compressibility of Pruned Reasoning Models via Long--Short Contrastive Pruning

The paper introduces Contrastive Set-Difference (CSD), a pruning method that targets neurons involved in redundant reasoning by contrasting activations on long versus short correct solutions. CSD is combined with an extended preference-based chain-of-thought compression that also considers problems a pruned model always or never solves. Applied to a 7B model, the approach reduces thinking tokens by 8–22% on math benchmarks while maintaining accuracy within 0.5 points compared to traditional pruning and compression pipelines.

arXiv AI
Sep 17

OBC-Prune: Outcome-Based Calibration for Large Reasoning Model Pruning

OBC‑Prune introduces an outcome‑based calibration approach for pruning large reasoning models, focusing on the causal importance of each reasoning sentence rather than uniform activation salience. By pairing correct and incorrect rollouts and using intervention‑based analysis, it assigns per‑token weights that guide one‑shot pruning methods such as SparseGPT, Wanda, and ALPS. Experiments on DeepSeek‑R1‑Distill‑Qwen models show consistent accuracy gains and shorter reasoning traces across multiple benchmarks at 40‑50% sparsity.

By Ha Lan Nguyen, Huy Hoang Tran, Trac-Duy Tran, Dung D. Le
arXiv AI
Aug 25

Revisiting the Effectiveness of LLM Pruning for Test-Time Scaling

The paper revisits the impact of pruning on large language models (LLMs) during test-time scaling (TTS). While prior work found that structured pruning degrades reasoning performance, this study shows that unstructured pruning—removing only specific redundant weights—can actually improve TTS performance on reasoning benchmarks for models s1.1-7B and Qwen3-8B, sometimes surpassing the full-weight models. The authors also examine how different layer-wise sparsity allocation strategies affect these outcomes.

By Ocean Monjur, Shahriar Kabir Nahin, Anshuman Chhabra
arXiv Computation and Language
5d ago

Direct Pass@$k$ Optimization for Thought Pruning: Balancing Quality and Diversity in Test-Time Reasoning

The paper introduces a pruning method for test-time reasoning that directly optimizes pass@$k$ by selecting a pool of partial solutions that maximizes the chance of at least one correct final answer. This approach balances quality and diversity automatically, avoiding separate design choices for each. Experiments on eight open-weight reasoning models show that the method outperforms existing quality-based and diversity-based pruning strategies, especially when a moderate number of partial solutions are retained.

By Mahdi Salmani, Adel Javanmard, Devansh Gupta, Meisam Razaviyayn
arXiv AI
Jun 30

Reconsidering Overthinking: Penalizing Internal and External Redundancy in CoT Reasoning

arXiv:2508. 02178v3 Announce Type: replace Abstract: Large reasoning models (LRMs) often exhibit overthinking, producing verbose Chain-of-Thought (CoT) traces that increase inference cost and obscure the underlying reasoning process.

By Taihang Zhen, Jialiang Hong, Kai Chen, Guang Yang, Junlan Feng, Wenpeng Zhu, Jing Huo, Yang Gao, Depeng Wang, Haitao Wan, Xi Yang, Fanyu Meng, Yuyao Zhang, Ji Qi, Xiangyu Zhou
arXiv Computation and Language
Sep 2

When Compression Helps and When It Hurts: Condition-Aware Analysis of Chain-of-Thought Distillation

The paper studies how to compress Chain-of-Thought (CoT) reasoning traces for smaller models. It examines three compression dimensions—importance criterion, restructuring level, and compression budget—across Math and General domains and Long/Short CoT regimes. Findings show that step-level pruning works best for shared reasoning backbones, token-level pruning needs symbol-aware signals, domain-specific restructuring effects differ, and training-time compression may not reduce inference cost, especially for Long-CoT students.

By Siyang Lyu, Xinghao Chen, Zhijing Sun, Tong Liu, Dawei Zhu, Xiaoyu Shen
arXiv Computation and Language
Sep 10

Demystifying Entropy-based Selection for Chain-of-Thought Compression in Large Reasoning Models

The paper evaluates entropy-based pruning for compressing Chain-of-Thought (CoT) reasoning in large models. Across multiple models and tasks, low- and high-entropy step selection shows no advantage over random pruning, and low-entropy token retention only helps on mathematical benchmarks due to the low entropy of numeric tokens. Patching a few CoT tokens with their original activations restores near-perfect performance, indicating that task information is distributed throughout the entire reasoning chain rather than concentrated in a small set of tokens.

By Sara Candussio, Daniel Scalena, Luca Bortolussi, Elisabetta Fersini, Malvina Nissim, Gabriele Sarti