A looped Transformer can decode 2.98 to 10.70 times faster by copying from its own context and screening guesses early
AspireAI community · arXiv (Wenyu Du, Stephen Chung)
Looped Transformers get extra computational depth by reapplying shared blocks, which makes conventional full-depth decoding expensive. CopyLoop is a training-free decoding algorithm that proposes multi-token suffixes by copying from repeated context, screens those proposals early at a shallow recurrent depth to filter out wrong branches, and schedules newer blocks concurrently while earlier ones are still verifying. Evaluated across six checkpoints from the Ouro, Raven and Huginn families on code generation and multi-step mathematical reasoning, it delivers decoding speedups of 2.98x to 10.70x over full-depth autoregressive decoding on base models and 2.74x to 3.52x on thinking models, consistently matching or beating competing baselines. Ablations attribute much of the gain to the synergy between shallow screening and continuous scheduling, and the method needs only lightweight model calibration.
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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.