llama.cpp just made low-bit KV cache dramatically more accurate, nearly for free.

PR #21038 adds graph-level Hadamard rotation of Q/K/V before caching, doing attention in the rotated space then rotating back, which makes standard quant types far more accurate in the KV cache. The benchmarks are not subtle: Qwen3 0.6B q5_1 KV perplexity drops from ~61.7 to ~14.1, and q4_1 from ~212 to ~22.3. For self-hosters this is a near-free path to longer contexts in less VRAM, and r/LocalLLaMA is tracking it as the successor to earlier TurboQuant work.