Official US Treasury exchange rates via US Treasury Fiscal Data. Used by federal agencies to report foreign-currency transactions in USD. Quarterly + ad-hoc updates per country/currency pair. Each row carries record_date, country, currency, country_currency_desc, exchange_rate, effective_date. Pair with `/api/fx/rates` (ECB Frankfurter, daily market rates) for cross-validation. Use Fiscal Data filter syntax — e.g. `filter=country:eq:Brazil` to scope to a single country.