Blog · Analysis
Why harness choice moves the bill 7x
August 14, 2026 · dshbase
DeepSeek's models are already cheap per token — but the harness you run them in can multiply the bill anyway. A coding agent re-sends the system prompt, tool definitions, history, and code on every step.
Prefix caching
If the beginning of a request matches a previous one, the provider reuses it. The cache hit rate is the share of input tokens that reused prior computation — higher = cheaper. A changed timestamp or reordered tool invalidates the cache.
Measured: 99.93% hit rate
The open-source agent Pi (on GitHub, ~86k stars) running DeepSeek reported a ~99.93% cache hit rate — a miss rate of 0.07%. Pi gives the model just four tools by default and keeps sessions append-only. Reported impact: ~¥19 per 1B tokens with caching vs ¥900+ without.
The 7x gap
A third-party benchmark (Composio) ran DeepSeek V4 Flash across 8 harnesses on real tasks: Pi ~$0.028 per successful task (cheapest), Claude Code ~$0.195 (nearly 7x Pi). Same model, different harness, very different bill.
Takeaway
- Minimal tool sets and append-only sessions are the biggest levers for cache hits.
- DSH aligns: small active surface, everything-as-plugin, PTC keeps intermediate data out of context.
Community-reported measurements, not official DeepSeek benchmarks — verify current pricing.