LaunchDarkly's REST API aims to maintain backward compatibility, but sometimes introduces breaking changes with new features and improvements. To accommodate this, they now support multiple API versions simultaneously, allowing users to migrate at their own pace without fear of unexpected behavior. Users can set the API version on a specific request by sending an LD-API-Version header or specifying it when creating an access token. Previously created tokens default to version 20160426. The company recommends explicitly setting the API version header in any client or integration built and only relying on the access token API version during manual testing.