DeepSeek's on-disk KV cache: exact prefix matching, 890 bytes per token, and a 50x input price gap
DeepSeek bills a cache hit on the input prefix at $0.003 per million tokens against $0.15 for a miss, and pays for that gap by keeping prefill state on disk. This piece covers what is stored, the cache-prefix units and append-only matching rule, the KV compression that made a disk tier practical (890 bytes per token on V4.1-Flash), the price ratios, and what third-party harness measurements say about real hit rates.