Whenever we make a backwards-incompatible change to the API, we release a new version of the API. (The current version is 2025-06-01.)

Buttondown determines the API version associated with a request in two ways:

• If a request includes a header with the key X-API-Version, Buttondown will use that value as the API version.
• If a request does not include a header with the key X-API-Version, Buttondown will use a pinned version associated with the newsletter. This pinned version can be found (and changed) in the "API" section of your settings page.
• If a pinned version is not present on the newsletter, Buttondown will use the latest version of the API.

We consider a backwards-incompatible change to be any change that could potentially break existing code that uses the API. This includes (but is not limited to):

• Renaming or removing fields from an object
• Removing or renaming an endpoint
• Changing the type of a field
• Changing whether or not a field is required
• Changing logic within an endpoint