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The agent scaffold mattered more than the model: rewriting it improved vulnerability detection by up to 25.8 points

AspireAI community · arXiv
The same frontier model can be a good vulnerability detector or a mediocre one depending mostly on the harness around it, the scaffolding that defines how it is prompted, called and judged. MetaVul treats the harness as the thing to optimise: starting from a seed structured-reasoning scaffold, it runs a workflow-based search over its own history of prior harnesses, using their trajectories, logs and metrics, and returns a set of Pareto-optimal harnesses that preserve the structured reasoning and verdict format. Optimisation used a 202-pair validation set, with 430 pairs held out. On both frontier and small models, the optimised harnesses improved pairwise vulnerability detection by up to 23.3 points on validation and up to 25.8 points on held-out data with a Pareto-frontier harness, and harnesses learned on one model transferred to another, lifting held-out pairwise accuracy by 14.7 points with no further optimisation. The honest caveat: the gains come from a specific dataset of paired vulnerable and patched functions, and the paper notes the approach was originally announced in September 2026.
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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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