> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lead.bank/llms.txt
> Use this file to discover all available pages before exploring further.

# Versioning and Backwards Compatibility

> How Lead versions its APIs, what counts as a breaking change, and the commitments Lead makes about notice, sandbox availability, and migration windows.

## **How Lead versions its APIs**

Lead versions **per resource**, in the URL path. Different resources sit at different versions because they ship and evolve independently — the version prefix tells you which contract you're on, and nothing else. The current version of every resource:

| **Resource**                                                                                                                            | **Current path prefix**                                                                                                                                                           |
| :-------------------------------------------------------------------------------------------------------------------------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Accounts, Applications, Blockchain Payments, Cards, Entities, Fundings, Lending disbursements (legacy), Originators, Subledger Balances | `/v0`                                                                                                                                                                             |
| Account Numbers, ACH, Events, Instant Payments, Internal Transfers, OAuth                                                               | `/v1`                                                                                                                                                                             |
| Wires                                                                                                                                   | `/v2` (`/v1 `remains available during the migration window — all partners must migrate by November 12, 2026; see the [Wires API V2 Migration Guide](/products/wire/v2-migration)) |

Sandbox simulators live under the corresponding version (`/v1/simulate/…`, `/v2/simulate/…`, plus `/v0/fundings/{id}/advance` and `/v0/simulate/lending/disbursements/{id}/advance`).

A lower number does not mean less stable: `/v0` resources are production APIs. A resource's version only increments when Lead must make a breaking change to it — as with Wires V2, driven by Fedwire's ISO 20022 mandates.

## **How we make changes**

**Additive changes are not breaking.** Lead may, without a version change: add new API endpoints; add new optional request fields; add new response fields; add new values to enums that are documented as extensible; add new event types; increase documented limits. Your integration should tolerate unknown response fields and unknown event types.

**Major breaking changes get a new version, notice, and sandbox time.** Removing or renaming fields, changing types or semantics, or removing endpoints happens only in a new resource version, announced in [Upcoming Changes](/upcoming-changes) with a migration guide, and available in sandbox before you're required to move. 

**Deprecations follow the same lifecycle.** When a version is scheduled for retirement, the timeline appears in [Upcoming Changes](/upcoming-changes) (Announced → Sandbox Available → Enforcement Soon → Released) and the old version keeps working until the stated enforcement date. 

**Beta APIs are the exception.** Resources labeled **API — Beta** may change without a version increment, but these changes will be announced in advance and our technical account team will work with you to implement the changes.