Each request to the Duffel API must include a `Duffel-Version` header so we know which
version of the API you want to use.

During our beta programme, we may make backwards-incompatible changes to the API at
short notice. When we do, you may need to make changes to your integration, or it'll
stop working.

Before we make any backwards-incompatible changes, we'll email registered users, post to
our [changelog](https://changelog.duffel.com) and tweet from
[@duffel_api](https://twitter.com/duffel_api).

Once we move out of beta, we'll release new, dated API versions when we make
backwards-incompatible changes to the API. We'll give at least three months'
notice before ending support for older versions.

We consider the following changes backwards-compatible:

- Adding new API endpoints
- Adding new attributes to responses from existing API endpoints
- Reordering attributes in responses from existing API endpoints
- Adding optional request parameters to existing API endpoints
- Changing the format or length of IDs
- Changing the `title` or `message` attributes of API errors
- Adding new types of services


Backwards Compatibility