anthropic prompt-caching cost-optimization typescript monitoring

Measure prompt cache hits to verify cost savings

Anthropic prompt caching silently fails in four ways (misplaced breakpoints, prefix drift, TTL expiration, unmeasured hit rates); wrap the SDK with explicit cache metrics to catch regressions.

May 27, 2026

Summary

Cache setup looks successful on first call but regresses silently—without measuring cache_read_input_tokens per request, you're likely paying full price on stale cached prefixes. Visibility prevents unexpected billing spikes.

Why it matters

Implementation verdict

Replaces manual response parsing and guesswork with a drop-in SDK wrapper that tracks hit rate, cost savings, and emits passive warnings on cache failures. Zero dependencies, ~50KB. Worth installing immediately if you're using Anthropic's cache API.

Sources

1.the only way to verify a call had hit the cache was to manually parse cache_read_input_tokens from the response usage on every request
2.The cache only hits if the cacheable prefix is byte-identical to what was cached
3.Anthropic recently dropped the default cache TTL from 1 hour to 5 minutes
4.A chatbot answering 1000 questions/day with a 10K-token system prompt easily hits 70%+ cost reductions

Dev Signal

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