Model merging, precision casting and low-rank rewriting are all YAML now, and coding agents can write the plans
AspireAI community · arXiv (cs.LG)
BrainSurgery consolidates checkpoint transformations that are normally scattered across Python code and separate task-specific tools into reusable declarative YAML plans over checkpoint tensors, with built-in targeting, validation, diffing and sharded export plus a web UI for inspection and plan construction. Across 13 settings, 11 benchmarks, 8 models, 4 architectures and sizes from 1.7B to 32B parameters, it reproduces three specialised systems' edits at comparable run cost and often lower memory use. A coding-agent study shows agents can reliably generate and review BrainSurgery plans, and that the plans are substantially shorter than equivalent Python.
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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.