{"i":20,"slug":"prompt-cache-break-even","chart":{"id":"cache-break-even-session-split","title":"One 10-turn session or ten 1-turn sessions: cost with and without the cache (calculation)","subtitle":"USD per 1,000 workloads of 10 requests that send the same prefix; each recorded session started in a new temporary folder, n = 4 later sessions; 0 met the read-more-than-write proxy, 95% Wilson 0% to 49%","kind":"grouped-bar","unit":"usd","yLabel":"USD per 1,000 workloads of 10 requests (list price)","series":{"$k":["name","points"],"$r":[["No cache (the same either way)",{"$k":["label","value"],"$r":[["Claude Sonnet 5.5",156.62],["Claude Opus 5.5 (cache read $0.2 per M)",313.12],["Claude Opus 5.5 (cache read $0.4 per M)",313.12]]}],["One 10-turn session, 1-hour cache",{"$k":["label","value"],"$r":[["Claude Sonnet 5.5",45.42],["Claude Opus 5.5 (cache read $0.2 per M)",76.71],["Claude Opus 5.5 (cache read $0.4 per M)",90.8]]}],["Ten 1-turn sessions, 1-hour cache (assumed no reuse of the new prefix)",{"$k":["label","value"],"$r":[["Claude Sonnet 5.5",313.24],["Claude Opus 5.5 (cache read $0.2 per M)",626.24],["Claude Opus 5.5 (cache read $0.4 per M)",626.24]]}]]},"note":"Calculation, not a bill: the same prefix, prices and 1-hour write as the cost-curve chart. Each recorded session ran in a new temporary working folder. On turn 1, 0 of 4 later sessions read more tokens than they wrote. This proxy cannot identify which earlier call supplied a cache entry. The split calculation assumes no shared reuse and a wholly new prefix, so it charges ten full writes. With reuse across sessions they would cost the same as one 10-turn session. The cause of the missing reuse was not tested here. The caching study protocol names the random temporary folder as one untested hypothesis. The table adds the 5-minute variants.","sourceIds":["calc-cache-pricing","agent-caching-consistency","price-anthropic","price-openai"]}}