Returns quote metadata: totals, currency, status, and expiration. The expires_at field shows when the quote expires if not confirmed.

The quote is generated asynchronously, so poll this endpoint. POST /experiments/{experiment_id}/submit returns before the quote exists; generating it involves a call to the payment provider. Until it lands this endpoint answers 404, which means not yet rather than never — the same contract GET /experiments/{experiment_id}/invoice follows. A 404 here is an expected step in the normal flow, not an error to report.

Poll until 200, or equivalently until stripe_quote_id appears on GET /experiments/{experiment_id}. A second or two is typical. Distinguish the two 404 causes by the experiment's own status: an experiment still in draft has not been submitted, so no quote is coming until it is.

{
  "amount_subtotal": 500000,
  "amount_total": 500000,
  "currency": "usd",
  "experiment_id": "019462a4-b1c2-7def-8901-23456789abcd",
  "expires_at": "2026-03-15T23:59:59Z",
  "stripe_quote_url": "https://billing.example.com/quotes/qt_1234567890",
  "updated_at": "2026-02-15T14:30:00Z"
}