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CoS-VQ jointly picked the token indices and their shared scale at a 2-bit budget, and lifted decode throughput from 21.9 to 36.7 tokens per second on Llama 3.1 8B

AspireAI community · arXiv
Low-bit weight quantization normally improves accuracy by raising the codeword dimension, which makes independent lookup and local codeword updates harder. CoS-VQ keeps low-dimensional codewords and instead optimises the hard indices and their shared scale together across positions. The hard part is scale-induced coupling: the best scale depends on the whole codeword combination, which changes candidate rankings, so pointwise updates stall even after scale is re-optimised. CoS-VQ collects candidates at multiple probe scales and builds a tangent separable upper bound, reducing candidate comparisons to lower envelopes of lines over positive scales. At a 2-bit target across six models it achieved the lowest average perplexity on five of six and the highest average downstream accuracy on three. On Qwen3.8-27B it reached 7.84 WikiText-2 perplexity against 8.29 for QTIP and 8.22 for LLVQ, and 82.83 on GPQA-D against 81.11 and 80.48. On Llama-3.1-8B-Instruct, decode throughput rose from 21.9 to 36.7 tokens per second, a 1.68x speedup at 2K context, with prefill essentially unchanged. The caveat: throughput was measured on a single RTX 4090.
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