[pron]

The APIs discussed in that case are only "classical" APIs, i.e. code APIs, not "web APIs", which are really protocols. Despite the fact that recently people have started calling protocols APIs, the two have huge differences from a copyright perspective[1], so that extrapolating from the former to the latter is tenuous, regardless of the ultimate outcome of that case.

Moreover, the court ruling makes it seem that if the intent is interoperability, fair use may apply (only the court rules Google's intent was not interoperability, as their implementation was intentionally incompatible).

Although in this particular case, it appears they can claim copyright violation on the documentation.

[1]: Most notably, in order to be copyrightable, a work has to be "fixed in a tangible medium of expression" (https://www.law.cornell.edu/uscode/text/17/102), i.e. you need to have a specific text (or image) that you can say, this is the work (although then even derivatives are protected). This is true for APIs, but not for protocols (or REST "APIs"). Whether this distinction makes sense to programmers or not is irrelevant. The same distinction holds for programs vs. algorithms: programs are "fixed in a tangible medium", and are subject to copyright, but algorithms are not, and not subject to copyright (but can be protected by patents).

[smarx007]

The docs are also MIT licensed, aren't they?

[pron]

I don't know, but the MIT license is given under conditions that can be violated.