4-bit Rotational Quantization | Weaviate

Introduced 4-bit Rotational Quantization (RQ4) with centering and outlier storage, achieving similar recall to 8-bit RQ but with a 45% heap reduction on a 1536-dimension vector dataset. Optimized encoding and distance kernels using SIMD (FWHT, UDOT, VPDPBUSD) for significant speedups (up to 6.1x for FWHT, 3.8x for RQ8 encoding). Improved memory access with prefetching for AMD64 and ARM64, contributing 7-11% query throughput and 12% faster imports. Demonstrated stable recall across datasets from 1M to 250M vectors.