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The contract is versioned by date. A version is the day it first reached production. Every response names the version it was rendered under in the Contract-Version header.

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Stating a version

Send the version your client was built against in the same header:

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What breaks

Ignore a response field you do not know. A breaking change passes through a window. The old behaviour is served until a stated day, at least 90 days after the release that announces it. The day never moves. Until then, every response that relies on it carries three headers:

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Open and closed enumerations

The reference marks every enumeration x-enum-open: true or false. You know a closed member when you stated a version that introduced it, when your request names it (a listing filtered by it), or when the record exists because you used the field or route introduced with it. Otherwise a listing leaves the record out, and a read of that one record is refused 406 contract_version_required. Its details.bound names the version to state.

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Versions

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Contract-Version, open and closed enumerations
Added
  • Contract-Version on every response, and as an optional request header.
  • invalid_contract_version (400): a version that was never published.
  • contract_version_required (406): a record in a closed member your version does not know.
  • x-enum-open on every enumeration in the reference.
  • Client guards on a product version: max_open_loans_per_client, max_outstanding_per_client, refuse_while_any_loan_overdue. Issuance and preview refuse past them with client_open_loans, client_exposure or client_overdue (422).
  • A limit decision: limit: true on a credit decision asks for the most the band admits; the decision answers ceiling and over_ceiling.
  • A line: line: true on a facility created from a limit decision, drawn by every purchase and refilled by repayment; supersedes and superseded_by when a line is renewed. New refusals facility_superseded and cannot_supersede (422).
  • A whole return: a goods return may state more than the outstanding principal. The answer states returned_whole, unwound_principal, principal_owed_back, interest_owed_back, beyond_the_loan and still_owed; the client’s obligations list returns and returned. A return that was refused for exceeding the outstanding principal is now served where the loan received principal.
  • The product frame’s field unit is open, and gains loans.
  • What falls due on a day: GET /v1/tenants/{tenant_id}/dues?on= lists every Client with something fallen due and unpaid on the date, with each owing Loan’s overdue, late and instalment as the payment options answer them and per-currency totals. Narrowed by only=late and min_days_past_due; one request examines at most twice limit Clients.
  • Your request bounds: GET /v1/tenants/{tenant_id}/bounds answers concurrent, patience_ms, per_second, burst and source. The reference states the defaults — 16, 2 seconds, 50 per second, 100 — and that requests within them are never refused for a bound.
  • A market’s rules: GET /v1/tenants/{tenant_id}/markets/{jurisdiction} answers the penalty cap’s form, the penalty base, capitalisation, whether a late fee may stand beside a penalty rate, acceleration, the tax rules, the disclosure convention, the calendar’s last covered day and the facility window, each with source and provisional. A jurisdiction nothing is supplied for is 404 not_found.
  • details.bound and details.observed on penalty_rate_above_cap, outside_window_bound, beyond_horizon and invalid_identifier: the bound the market’s rules state (or the identifier pattern) and the value that exceeded it.
  • effective on every product configuration read, create and preview: every field the frame declares, with its value and source (stated or default). values is unchanged.
  • advisories on a configuration create, a version create and both previews, with the open codes first_period_may_fall_next_day and no_tolerance. An advisory refuses nothing.
  • percent beside the ratio on a decision’s, a resolution’s and a facility’s rate: the decimal percentage a loan states.
  • rate is optional on a preview and an issuance under a facility, which then takes the facility’s rate; penalty_rate is optional under a version whose penalty corridor is a single point, which then takes the point.
  • Lookup keys: a word of your own that names the configuration version you sell, the same in every environment. PUT, GET and DELETE /v1/tenants/{tenant_id}/product-lookup-keys/{lookup_key}, and GET /v1/tenants/{tenant_id}/product-lookup-keys, which resolves up to ten keys in one read with a repeated lookup_key. A key that names another version moves only with transfer: true; otherwise lookup_key_taken (409), with the configuration and version it names in details. No selling request changes: sell under the pair the read answers.
  • Server-Timing on every response at both doors: total always, and queue, conn, db and derive once the caller is authenticated. See reading Server-Timing.
  • A dated read answers from one moment of the client’s record: a receipt recorded while the read runs is wholly in the answer or wholly out of it. No field or figure changes.
Deprecated: nothing new. vat_rate_bps stays deprecated until 2027-01-15, from 2026-10-15.Closed enumerations: no new member. A caller stating this version and one stating none are served the same bodies.Breaking: one refusal, at the console’s policy authoring. A policy version whose approving band’s rate has no decimal of at most eight places as a percentage — one third, say — is refused at validation and publication. No loan could ever be issued under such a band, so nothing issuable is lost, and no window applies.
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The baseline
What the API served when versions began. A request stating no version is served this.DeprecatedUntil that day a statement carrying vat_rate_bps is accepted with the field ignored. The answer carries Deprecation: @1799971200, Sunset: Fri, 15 Jan 2027 00:00:00 GMT and a Link to this entry.Reached production the same day, before versions existedThese closed-enumeration members shipped on 2026-10-15, before the rule above. They are part of the baseline and are served to every caller.A listing still leaves held, expired and voided loans out unless state names them.