We try to keep a backwards compatibility of the existing API. If the API changes in an incompatible manner this is listed explicitly in the "important release notes" section of each releases changelog.
Adding new fields to an entity is not considered as incompatible change. But if a field is being removed, renamed or the data format changes, this is considered as incompatible change.
Each answer of the API contains a HTTP header field "X-Translate5-Version" which contains the current version of translate5.
All GET calls without an ID provide a list of resources. With the GET Parameter “filter” this list can be filtered. In general all fields are filterable. Exceptions in single cases.