Abiquo is committed to maintaing backwards compatibility for 2 minor releases. If for some reason, backwards compatibility were not possible to maintain, Abiquo would detail the changes in the API Changelog. For example, Abiquo 5.4 should be compatible with 5.3 and 5.2. The best practice to ensure compatibility is to use the version number in the header of your API request with the media type and content type.
For major versions such as 6.0, Abiquo will make a best effort to maintain compatibility with at least the previous version. Abiquo will provide details of any changes in the API Changelog.