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Trainable vector quantization gives 2-bit LLM weights a near-lossless result instead of a training-free guess

AspireAI community · arXiv
Extreme weight compression degrades LLM quality, and the usual vector-quantization recipes cannot recover it because the quantized parameters are discrete. TVQ uses straight-through estimation and trainable latent weights to make vector-quantized LLMs trainable by gradient descent, then applies it in a block-wise knowledge-distillation setup. The authors report state-of-the-art quality for low-bit post-training quantization with a modest training budget and a plain PyTorch implementation, including near-lossless 2-bit quantization of LLaMA2-70B with about a 1% accuracy drop on common question-answering benchmarks. The headline figure comes from one model family and older QA benchmarks, so whether that 1% holds for modern instruction-tuned models is untested here.
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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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