Prompt caching: absolute API cost evidence

28 October 2026 · replacement for the main Care Access percentage-only example

Anthropic’s 9 August 2026 cookbook reports saved runs on ten synthetic insurance claims using Opus 5 at high effort. Its final configuration table carries forward the earlier measured runs; these are not additional replications.

Configuration	USD per claim	Correct	API requests
No cache, one trial	0.2906	10/10	36
Cached, trial 1	0.1498	10/10	34
Cached, trial 2	0.1512	10/10	35

The cached mean is $0.1505; the reduction against $0.2906 is 48.21%, displayed as about 48%. Bars share a zero origin and use those exact costs. The small evaluation does not demonstrate production accuracy or isolate every stochastic difference. Costs cover the model API, including cache writes/reads and output, not the complete application. No latency result is inferred. No annual or 10,000-task bill is claimed.

Slide 14 shows the absolute comparison and the synthetic-test label. Narration explains the range, sample and scope. Slide 15 then explains stable-prefix reuse with a separately labelled current Opus 5.5 price example. Care Access remains historical source material; its absolute baselines remain undisclosed.

Source register: ../03-sources/2026-10-28-caching-benchmark.json. Chart inputs: ../02-data/2026-10-28-caching-benchmark.csv.