The documentation of the newest Development Kit is available on the Archicad API site.
The released Development Kit starting from version 25 can be found in the GitHub repository.
Older versions are present on the Archicad API developer site.
In order to register as an Archicad API developer, please visit the developer site.
Content of this repository (the Development Kit and the API documentation) is licensed under the Graphisoft Software License Agreement. See the LICENSE file for details.