Anthropic's cache savings alert flagged $0.16 gain while Claude Code quietly saved $62,934

Anthropic emailed an engineering team warning that their low prompt cache hit rate could save up to 64% on direct API costs, but the actual saving amounted to just $0.16 on $0.25 of eligible spend. The direct API traffic involved only 16 short, unique single-turn calls averaging 90 tokens — well below the minimum threshold for caching — making a zero hit rate structurally inevitable. Meanwhile, Claude Code traffic that the email explicitly excluded told a different story: across 71 days and 158 sessions, automatic caching cut input costs by 83.9%, saving an estimated $62,934 at list price without any manual configuration. The team also tested a popular 'keep-alive ping' optimization, finding it would have cost $2,009 in cache reads to recover at most $1,913 in savings, making it a net loss. They attribute the ping strategy's irrelevance to Claude Code already routing most cache writes into the one-hour TTL bucket, a feature that renders the workaround obsolete.