TL;DR from the article:

• FP8 via --kv-cache-dtype fp8 remains the best default for KV-cache quantization: it provides 2x KV-cache capacity with negligible accuracy loss, while matching BF16 on most performance metrics and substantially improving them in memory-constrained serving scenarios.
• TurboQuant k8v4 does not provide any significant advantage over FP8: it only provides modest KV-cache savings (2.4x vs 2x) which are not worth the consistent negative impact on throughput and latency metrics.
• TurboQuant 4bit-nc is likely the most practical TurboQuant variant: it helps under KV-cache memory pressure, but trades the extra capacity for moderate accuracy, latency, and throughput costs. It may still be viable for edge deployments where memory is the dominant constraint.
• TurboQuant k3v4-nc and 3bit-nc show meaningful accuracy drops, especially on reasoning and very long-context tasks, while also substantially degrading latency and throughput. This makes them poor candidates for production deployments.