900 hours of video and 5,000 reviewed questions, and a harness that lifted all 13 tested models by more than half
AspireAI community · arXiv
Long-horizon memory is where video models fall apart, so this paper ships both a benchmark and the scaffolding that fixes it. The LongVideo dataset holds about 900 hours of video and over 5,000 manually reviewed questions spanning visual, textual and spatiotemporal reasoning at different context lengths, and the 4DMemory Harness bundles four complementary skills, more than 22 specialized tool models and a model-specific retrieval-augmented generation system. Across 13 leading models, standalone foundation models struggled with the long-horizon tasks while the harness improved every one of them by over 50 percent, and the same models dropped by more than 10 percent on 4DMemoryBench compared with the previous benchmark, which is the part worth noting: the harder benchmark is where the gap opened, and the harness is what closed it.
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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.