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Watermark Basins found a signal that survives model compression, and it caught 79 percent of distilled models where token-level checks caught 29 percent

AspireAI community · arXiv
*Existing detectors of API-based model distillation work on token-level statistics, and those statistics quietly wash out when a teacher is sampled at low temperature.* Watermark Basins looks for the signal somewhere more durable. During fine-tuning, watermarked teacher traces leave a key-specific geometric signal in parameter space that sits orthogonal to the ordinary task-specific fine-tuning subspace, so the detector maps generated text to gradient representations with a fixed clean probe model, projects out the task directions and tests whether what is left aligns with the watermark basin. WM-Basin queries the suspect model through its API only - no weights, no logits. At a strict 0.1 percent false-positive rate it detects 79 percent of distilled models at n-gram=1 and 45 percent at n-gram=3, against 29 percent and 1.3 percent for the strongest token-level baseline, across students from 135M to 8.2B parameters on mathematical reasoning. Because the signal lives in a persistent basin it also survives quantization, pruning and reinforcement-learning post-training. The limitation: the evaluation is on math reasoning distillation, and detection rate still falls by more than half at n-gram=3.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.
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