4-bit Rotational Quantization

Weaviate 1.39 expands its Rotational Quantization (RQ) support with a new 4-bit option and broad performance improvements to 8-bit and 1-bit RQ, including SIMD-accelerated rotations, encoding, distance kernels, and CPU prefetching. The release substantially speeds encoding and distance calculations, improves import throughput, and introduces 4-bit RQ variants that reduce heap usage by about 45% relative to 8-bit while often delivering comparable or better recall-versus-query-performance results through lower memory-bandwidth demands. Optional mean centering and exact storage of two extreme rotated coordinates improve 4-bit recall, particularly for embeddings with nonzero means or anisotropic distributions, while rescoring candidates using original vectors can further approach exact-search accuracy. Tests from 1 million to 250 million vectors found RQ recall remained broadly stable, though ANN index settings may still require sharding at larger scales. Comparisons with TurboQuant found that centered RQ4 generally matched or outperformed enhanced TurboQuant configurations, while RQ also supports efficient 8-bit operation. RQ4 is available through the existing Weaviate RQ configuration using a 4-bit setting, with centering enabled as an optional feature, whereas 8-bit RQ remains the default in Weaviate Cloud.

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