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1. Closely follows the JSON API specification.  v2 was a completely custom and non-standard request and response structure.
2. Uses industry standard HTTP verbs/methods (GET, PUT, etc) and endpoint URLs.  v2 used one URL and everything was a POST.
3. API Key is accepted only on Authorization header.  In v2 the API Key was taken from the URL.
4. Multiple sort values using +/- are supported.  In v2 only one sort field was supported with asc/desc.
5. Random sort now available.  In v2 random was not available.
6. Distance filter is it's own properties in POST body and supports either miles or kilometers.  In v2 the radius filter was included with any other filters.
7. Related objects can be included in the response body but separate (eg., Organization along with Animals).  In v2 related object fields were either mixed with the requested object or an additional request to the API was necessary.
8. Some fields are considered meta and returned separately from the other properties (see the meta Option).  In v2 all fields were the same, even if they were meta.
9. Endpoint URLs can include view names to automatically add filters.  In v2 filters could only be added in the POST body.

Swagger definition available

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