[bnprks]

Yeah, the crux of the issue would definitely be whether use of an API is prohibited by default under copyright law for a country (i.e. does using a library make something a derivative work of the library). In the US, at least, the Google v Oracle case makes me think this is worst case fair use (for many contexts) and best case too functional to be covered by copyright in the first place.

Though I can certainly imagine that a multinational company might not be confident of the copyright status of API usage in all countries they operate in.

[missjellyfish]

I'd further argue that it would be important if your program does anything useful without the GPL parts; if so, you can probably argue that it is not a derivative work. If you however only build an extension to some GPL'ed software that fundamentally needs the GPL'ed code to properly function and cannot (easily) be used by any other software, then you probably will create a derivative work.