We are working on our own AddOn for Archicad but we use simultanously more Archicad versions. Is there a way to create custom AddOns using the API only once with cross-version functionality (e.g. for 25, 26 and future releases) or does the AddOn need to be built separately for each version of Archicad by using each version's respective API Development Kit/SDK?
You have to compile your Add-On for every Archicad version separately, but you can use the same code base for all versions. Sometimes the API changes so you have to write some code to make it work with all versions.