# API Versioning

The launch client API is versioned with a single URL prefix: `/v1`. Pin that prefix in your base URL and treat response objects as additive.

## How to call v1

Use URI versioning. The version is the first path segment after the host:

```
GET https://sandbox.api.billerapi.com/v1/billers
POST https://api.billerapi.com/v1/link-tokens
GET https://api.billerapi.com/v1/bills
```

> **Note — No version header**
> BillerAPI does not use an Accept-Version header. The version in the URL is the version you get.

## Additive responses

Within `/v1`, BillerAPI may add fields, enum values, event types, and error codes. Integrations should ignore unknown response fields and handle unfamiliar `error_code` values using the HTTP status and error type.

**Can change inside v1**

- New optional response fields
- New optional request parameters
- New webhook event types
- New error codes

**Stable inside v1**

- Existing field names and meanings
- Existing required request parameters
- Existing authentication model
- Existing route semantics

## Related

- [Authentication](/docs/guides/authentication) - Bearer API keys and access tokens
- [Error Handling](/docs/concepts/errors) - coded errors and request IDs
- [OpenAPI Spec](/docs/concepts/openapi) - generated client schema