Permafrost

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        freeze the prefix · melt the bill

A Claude Code plugin that keeps DeepSeek's prompt cache hitting when Claude Code would otherwise bust it.

cache-stable passthrough proxy · deterministic tool order · env freeze+delta · cold-anchor coalescing · live hit-rate statusline · zero deps

Pointing Claude Code at DeepSeek's Anthropic-compatible endpoint is cheap, and a
vanilla session already hits DeepSeek's cache ~90% on its own — CC's system
prompt is shared across users, so it stays warm. The cache breaks when your
tool list isn't stable: MCP servers connect and reshuffle it, and because
tools render *first* in the cached prefix, any reorder busts everything from
byte 0. Permafrost sits between CC and DeepSeek and rewrites the cache-relevant
bytes so the tools + system anchor stays byte-identical turn after turn — then
streams the reply straight back.

Do you actually need it?

We ran bare DeepSeek vs Permafrost head-to-head on the live API and read
DeepSeek's real cache tokens. The honest result is two-sided:

If you run plain single-agent CC, you don't need this — DeepSeek already does
the job. Permafrost earns its keep on the second row: tool churn busts the prefix
at byte 0 and bare collapses to 33%; the deterministic sort holds it at 71%
(reproduce: e2e/tool_order_ab.py). So it's for users with
MCP servers, heavily customized setups whose anchor isn't the shared-warm
one, or parallel subagent fan-outs on cold anchors.

On cost: DeepSeek is ~11× cheaper than Claude on pricing alone (cache-hit
input $0.0028 vs $0.30 /1M) — that's DeepSeek, not us, the moment you switch
endpoints. Permafrost's *additional* contribution is keeping the cache hitting
when it would otherwise bust (the 33% → 71% roughly halves the bill on a
tool-churning…