There is a whole open-source ecosystem aimed at cutting LLM cost. The trick to evaluating any of it is to ask which of the three cost lines it attacks — cached input (0.1×), uncached/written input (1×/2×), or output (the priciest, never cached) — and then whether it does so without forfeiting the model-scoped prompt cache.
That last clause is the recurring catch, and it's the throughline of this entire guide:
Anything that rewrites the request prefix per turn forfeits the model-scoped prompt cache. A tool nets real savings only if it (a) preserves the cached prefix byte-for-byte, or (b) attacks a cost line the cache doesn't cover — namely output.
We'll walk the ecosystem in cost-line order: input/cache compressors, then the output compressor, then the model routers, then what routing actually costs inside Claude Code.
Input / cache-line compressors
