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SAEBench: A Comprehensive Benchmark for Sparse Autoencoders in Language Model Interpretability
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Introduces SAEBench, an eight-metric benchmark suite for sparse autoencoders covering concept detection, interpretability, reconstruction and feature disentanglement, and releases over 200 SAEs trained across seven architectures on Gemma-2-2B and Pythia-160M.
Problem
Sparse autoencoders are typically evaluated with unsupervised proxy metrics (sparsity-fidelity tradeoff) whose relevance to practical interpretability is unclear, so progress is hard to measure.
Approach
A standardized multi-metric evaluation suite (sparse probing, feature absorption, RAVEL, unlearning, SCR, TPP, automated interpretability, loss recovered) plus two new zero-ablation disentanglement metrics (SCR and TPP), applied to a large sweep of SAE architectures, widths and sparsities; shows that proxy metric gains do not reliably transfer to downstream metrics.
Key results
- Matryoshka BatchTopK SAEs achieve best scores on 5 of 8 metrics in typical L0 range 40-200, despite worse sparsity-fidelity frontier.
- Matryoshka is the only architecture whose feature disentanglement (absorption, SCR) improves with dictionary width; other architectures show inverse scaling.
- The ReLU SAE is outperformed by other methods on 5 of 8 metrics and performs worst on loss recovered.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use Matryoshka BatchTopK instead of other evaluated SAE architectures | SAEs on Gemma-2-2B, 65k latents, L0 40-200 · Gemma-2-2B, 65k latents, L0 40-200 | feature disentanglement (RAVEL, SCR, and TPP) | Helped |
| Use Matryoshka BatchTopK instead of other evaluated SAE architectures | SAEs on Gemma-2-2B, 65k latents, L0 40-200 · Gemma-2-2B, 65k latents, L0 40-200 | sparsity-fidelity frontier | Hurt |
| Replace ReLU with other evaluated SAE architectures | SAEs on Gemma-2-2B, 65k latents · Gemma-2-2B, 65k latents | loss recovered | Helped |
| Replace ReLU with other evaluated SAE architectures | SAEs on Gemma-2-2B, 65k latents · Gemma-2-2B, 65k latents | absorption, SCR, RAVEL, and TPP | Helped |
| Use ReLU instead of other evaluated SAE architectures at L0 > 200 | SAEs on Gemma-2-2B, 65k latents · Gemma-2-2B, 65k latents, L0 > 200 | 1-sparse probing | Helped |
| Increase dictionary width from 4k to 65k | SAEs across evaluated architectures · Gemma-2-2B, dictionary width 4k to 65k | automated interpretability | Helped |
| Increase dictionary width from 4k to 65k for non-Matryoshka architectures | Non-hierarchical SAEs · Gemma-2-2B, dictionary width 4k to 65k | feature disentanglement and concept detection | Hurt |
| Increase dictionary width from 4k to 65k for Matryoshka | Matryoshka SAEs · Gemma-2-2B, dictionary width 4k to 65k | spurious correlation removal | Helped |
| Increase L0 sparsity | SAEs across evaluated architectures · Gemma-2-2B, L0 > 400 | RAVEL and targeted probe perturbation | Helped |
| Use moderate L0 values of 50-150 rather than a task-specific extreme | SAEs across evaluated architectures · Gemma-2-2B, L0 50-150 | overall metric trade-off | Mixed |
| Train for 50M tokens rather than stopping earlier | 16k TopK and ReLU SAEs · Gemma-2-2B, 16k TopK and ReLU checkpoints | benchmark metrics | Helped |
Surprising findings
- Sparse probing provides limited differentiation between architectures, widths and sparsities, with scores in a narrow range.
- Feature disentanglement metrics (TPP, RAVEL) prefer higher L0 values (>400), diverging from the conventional 20-200 range.
Limitations
- Supervised metrics only cover concepts with ground truth data, so they examine a small fraction of latents and some are noisy.
- Unlearning evaluation is constrained because Gemma-2-2B has weak baseline performance on most unlearning test sets.
- Results are limited to Gemma-2-2B and Pythia-160M and a single middle layer per model.
Experimental setup
Datasets: The Pile OpenWebText WMDP-bio WikiText MMLU bias_in_bios Amazon Reviews Europarl GitHub AG News RAVEL
Benchmarks: SAEBench sparse probing feature absorption RAVEL unlearning (WMDP-bio) spurious correlation removal targeted probe perturbation automated interpretability loss recovered
Metrics: loss recovered L0 sparsity accuracy interpretability score absorption score disentanglement score
Baselines: ReLU SAE TopK SAE BatchTopK SAE Gated SAE JumpReLU SAE P-Annealing SAE MatryoshkaBatchTopK SAE PCA
Builds on: RAVEL SHIFT Feature Absorption Gated SAE TopK SAE Matryoshka SAE JumpReLU SAE Gemma Scope
Closest papers by meaning
- Improving Sparse Decomposition of Language Model Activations with Gated Sparse Autoencoders (NeurIPS 2024 · similarity 0.94)
- Are Sparse Autoencoders Useful? A Case Study in Sparse Probing (ICML 2025 · similarity 0.93)
- Scaling and evaluating sparse autoencoders (ICLR 2025 · similarity 0.92)
- Rethinking Evaluation of Sparse Autoencoders through the Representation of Polysemous Words (ICLR 2025 · similarity 0.92)
- Automatically Interpreting Millions of Features in Large Language Models (ICML 2025 · similarity 0.92)
- Low-Rank Adapting Models for Sparse Autoencoders (ICML 2025 · similarity 0.92)
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