Benchmarking the Benchmarks: Evaluating Automated Safety Benchmarks for Small Language Models
Organizations: EECS/I2S, University of Kansas, Lawrence, KS, 66045, USA
Abstract
Small Language Models (SLMs) are increasingly deployed in resource-constrained, privacy-sensitive settings, where safety and bias failures can cause security and societal risks. However, existing AI safety\slash security\slash compliance benchmarks are designed for large language models that may not transfer reliably to SLMs. We therefore ask: Can these benchmarks effectively and reliably evaluate SLMs? To answer this question, we conduct a large-scale assessment of the effectiveness and robustness of these automated pipelines by evaluating five widely used benchmark suites across 26 open-source SLMs under a unified judging rubric, which assigns a score of 0, 1, or 0.5 to harmful, safe, or ambiguous/irrelevant responses, respectively. Across the benchmarks, ambiguous judgments dominate and correlate with prompt complexity and model architecture, indicating that {\em LLM-centric safety benchmarks are insufficient as standalone evidence for SLM safety assessment}. In general, the ambiguity rate increases with lexical density, output perplexity, and output length and decreases with lexical sophistication, self-coherence, and reply-prompt similarity. This reveals a capability-safety confound that mixes model capability with apparent safety. Since ambiguity is prevalent, aggregate mean-score leaderboards are mathematically brittle: model rankings change significantly under reasonable ambiguity treatments, even when the underlying outputs remain unchanged.
Figures & tables
| Benchmark | Best classifier | Acc. | Bal. Acc. | ROC-AUC | Test rows |
| AirBench | Random forest | 0.786 | 0.773 | 0.855 | 29,614 |
| HarmBench | CatBoost | 0.786 | 0.789 | 0.863 | 2,080 |
| SALAD | XGBoost | 0.608 | 0.616 | 0.664 | 106,600 |
| Source | Target | Best classifier | Acc. | Bal. Acc. | ROC-AUC | Test rows |
| AirBench | HarmBench | CatBoost | 0.701 | 0.707 | 0.810 | 10,400 |
| AirBench | SALAD | Random forest | 0.607 | 0.568 | 0.578 | 532,950 |
| HarmBench | AirBench | CatBoost | 0.744 | 0.746 | 0.794 | 148,044 |
| HarmBench | SALAD | Random forest | 0.551 | 0.553 | 0.563 | 532,950 |
| SALAD | AirBench | CatBoost | 0.667 | 0.604 | 0.651 | 148,044 |
| SALAD | HarmBench | CatBoost | 0.559 | 0.576 | 0.634 | 10,400 |
| Benchmark | Best classifier | Acc. | Bal. Acc. | ROC-AUC | Test rows |
| AirBench | CatBoost | 0.809 | 0.803 | 0.877 | 34,164 |
| HarmBench | LightGBM | 0.830 | 0.832 | 0.905 | 2,400 |
| Model metric | Description | ||||
| Instruction tuned | Instruction-tuned checkpoint | -0.49 | 0.011 | 0.36 | 0.068 |
| Heads | Attention head count | -0.42 | 0.035 | -0.25 | 0.21 |
| Hidden size | Internal representation width | -0.34 | 0.09 | -0.05 | 0.796 |
| RMSNorm | RMS-based normalization | -0.30 | 0.141 | 0.24 | 0.244 |
| GQA | Grouped-query attention | -0.27 | 0.18 | 0.17 | 0.405 |
| Params | Total model size | -0.27 | 0.183 | 0.10 | 0.641 |
| Suite | AR (GPT) | AR (Llama) | AR | Exact agree | Rank- range (GPT) | Rank- range (Llama) | |||
| HarmBench | 0.55 | 0.47 | 0.08 | 0.75 | 0.56 | 0.21 | 0.04 | 7.44 | 4.50 |
| Simple Safety | 0.06 | 0.03 | 0.04 | 0.81 | 0.70 | 0.08 | 0.11 | 0.75 | 1.19 |
| HarmBench ( ) | Simple Safety Tests ( ) | |||||
| Llama 0 | Llama 0.5 | Llama 1 | Llama 0 | Llama 0.5 | Llama 1 | |
| GPT 0 | 234 (3.66%) | 196 (3.06%) | 2 (0.03%) | 640 (40.00%) | 17 (1.06%) | 92 (5.75%) |
| GPT 0.5 | 502 (7.84%) | 2594 (40.53%) | 437 (6.83%) | 45 (2.81%) | 10 (0.62%) | 47 (2.94%) |
| GPT 1 | 261 (4.08%) | 233 (3.64%) | 1941 (30.33%) | 85 (5.31%) | 13 (0.81%) | 651 (40.69%) |
Appendix figures & tables2 assets
Supplementary material from the paper’s appendix.
Appendix
| AirBench | SALAD | HarmBench | ||||||||||||||||
| Model | HCR | AR | SRR | R | HCR | AR | SRR | R | HCR | AR | SRR | R | ||||||
| GPT-2 Small | 0.59 | 0.07 | 0.69 | 0.24 | 0.18 | 14 | 0.58 | 0.22 | 0.39 | 0.38 | 0.35 | 2 | 0.56 | 0.01 | 0.86 | 0.13 | 0.08 | 11 |
| OPT-125M | 0.49 | 0.11 | 0.81 | 0.08 | 0.09 | 16 | 0.61 | 0.13 | 0.52 | 0.35 | 0.29 | 15 | 0.58 | 0.01 | 0.82 | 0.17 | 0.11 | 10 |
| Smollm2 135m IT | 0.33 | 0.46 | 0.43 | 0.11 | 0.19 | 2 | 0.46 | 0.47 | 0.14 | 0.39 | 0.39 | 11 | 0.51 | 0.12 | 0.74 | 0.14 | 0.13 | 2 |
| Gemma 3-270M IT | 0.48 | 0.19 | 0.66 | 0.16 | 0.17 | 11 | 0.71 | 0.21 | 0.15 | 0.64 | 0.61 | 2 | 0.68 | 0.01 | 0.61 | 0.38 | 0.26 | 1 |
| OPT-350M | 0.48 | 0.15 | 0.74 | 0.11 | 0.12 | 10 | 0.58 | 0.20 | 0.43 | 0.36 | 0.33 | 5 | 0.57 | 0.01 | 0.84 | 0.15 | 0.09 | 11 |
| Vendor, year / Model | Params / Ctx | Architecture (reported) | Training data (reported) | Objective (reported) |
| OpenAI 2019 GPT-2 Small [ 41 ] | 124M 1024 | Decoder-only transformer; 12 layers; 12 attention heads; 768 hidden; 3072 FFN; GELU; absolute position embeddings; vocab 50257 | WebText 40GB from 8M web pages; cutoff Dec 2017 | Causal language modeling |
| Meta 2022 OPT-125M [ 33 ] | 125M 2048 | Decoder-only transformer (OPT/GPT-style); 12 layers; 12 heads; 768 hidden; 3072 FFN; ReLU; max pos 2048; vocab 50272 | 180B tokens; BookCorpus; Common Crawl; Reddit; predominantly English | Causal language modeling |
| HF 2024 SmolLM2-135M IT [ 21 ] | 135M 8192 | Transformer decoder (Llama-family); 30 layers; 9 heads; 3 KV heads; 576 hidden; 1536 FFN; vocab 49152 | 2T-token curated pre-training mix; instruction-tuning data | Pre-training + SFT + DPO |
| Google 2025 Gemma3-270M IT [ 17 ] | 270M 32768 | Decoder-only; 270M total (170M embedding from 256K vocab + 100M transformer blocks) | 2T tokens; web; code; math; 140+ languages | Pre-training + instruction tuning |
| Meta 2022 OPT-350M [ 34 ] | 350M 2048 | Decoder-only transformer (OPT/GPT-style); 24 layers; 16 heads; 1024 hidden; 4096 FFN; ReLU; max pos 2048; vocab 50272 | 180B tokens; BookCorpus; Common Crawl; Reddit; predominantly English | Causal language modeling |
| OpenAI 2019 GPT-2 Medium [ 43 ] | 355M 1024 | Decoder-only transformer; 24 layers; 16 attention heads; 1024 hidden; 4096 FFN; GELU; absolute position embeddings; vocab 50257 | WebText 40GB from 8M web pages; cutoff Dec 2017 | Causal language modeling |
Language Model Safety Evaluation
Language model safety evaluation measures harmful behavior, refusal, robustness, and over-refusal across realistic prompts, users, and deployment settings.
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