HyperRepair recovers general capabilities that fine-tuning erodes, using a hypernetwork and no target-domain examples
AspireAI community · arXiv (cs.CL)
Fine-tuning a language model on a domain usually weakens its general abilities, and existing methods trade domain specialisation against general capability. HyperRepair treats recovery as an inference-cost problem: a hypernetwork learns from repairs trained on source models and uses activation fingerprints summarising the change from the pretrained backbone to generate a tailored Repairing Side Net, whose prompt-conditioned gate applies corrections selectively. That lets recovery transfer to models from adaptation domains never seen during training, without target-domain examples or additional optimisation. Across two model families, 12 LoRA adaptation datasets and 15 general benchmarks, the framework recovers 93.4 percent of the base models' average general score while retaining 99.5 percent of the fine-tuned models' average domain score. The evaluation covers LoRA adaptations rather than full fine-tuning, and the reported figures are averages across benchmarks.
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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.