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

# API versioning

> The URL major version /v1 plus the X-ENSC-API-Version date header. The current version is 2026-09-15 and the SDK pins it.

The API is versioned in two places:

* **The URL major version**, `/v1`, for the shape of the API as a whole. Every route on this site lives under `/v1`.
* **The date version**, sent as the `X-ENSC-API-Version` header, for the contract you were built against. The current version is `2026-09-15`.

```
X-ENSC-API-Version: 2026-09-15
```

Pinning the date version means an API change cannot silently alter behaviour under a deployed integration. Every response carries the version it was served with in its own `X-ENSC-API-Version` header.

## What the SDK does

`@ensc/sdk` sends the pinned header on every request. `DEFAULT_API_VERSION` is `2026-09-15` in 0.3.0 and later; 0.4.1 requires API date version `2026-09-15` (unchanged from 0.4.0). Upgrading the SDK is how you adopt a newer date version. Read the [changelog](/changelog) before adopting a newer version.

## What changed in 2026-09-15

Version `2026-09-15` introduced mandatory payload encryption: every write body is an ENSC-ENC-V1 envelope, and every successful response is an ENSC-RESP-V1 sealed body. Plaintext merchant writes are refused with `ENSC_ENCRYPTION_REQUIRED`. SDK versions before 0.3.0 send plaintext requests the API refuses, and versions before 0.4.0 call routes that no longer exist and receive `ENSC_NOT_FOUND`. The full list is in the [changelog](/changelog).

## Webhook payloads

A webhook endpoint can pin the payload version its deliveries use (`apiVersion` when you register it; defaults to the current version). Each delivery states its version in the body (`apiVersion`) and in the `X-ENSC-API-Version` header. See [Webhooks](/guides/webhooks#registering-an-endpoint).

## The published reference

The API reference tab of this site is generated from the OpenAPI document for `2026-09-15`, and each operation there shows the `@ensc/sdk` call that makes it. The API serves the same material itself:

* [https://api.ensc.prosperavest.com/v1/docs](https://api.ensc.prosperavest.com/v1/docs): the live reference.
* [https://api.ensc.prosperavest.com/v1/openapi.json](https://api.ensc.prosperavest.com/v1/openapi.json): the public OpenAPI 3.1 document, the same file this site's API reference tab is generated from.

When a new date version ships, a new document is published and the changelog records the differences.