ChatGPT, Claude, Claude Code, Cursor, Copilot — same spec, same input, measured across test count, coverage quality, and engineering time. Every major tool can generate API tests. The question is: how many tests, how good, and at what cost in engineering time? To find out, we ran a structured study using the Stripe Payments API as the benchmark, specifically the POST /v1/payment_intents endpoint for single-API tests, and a representative slice of the full Stripe spec for whole-spec tests. We scored each approach across four dimensions: field coverage, test type depth, security coverage, and semantic accuracy. What a Truly Exhaustive Suite Actually Covers Before looking at the results, it's worth being precise about what "exhaustive" means.…