The Supreme Court conclusively established that Google's use of the APIs was fair use under copyright law, so they did not need to reach the underlying question

The Supreme Court conclusively established that Google's use of the APIs was fair use under copyright law, so they did not need to reach the underlying question. I believe it would be safe to conclude that API descriptions such as header files are protected by copyright even in their essentials, that fair use is necessary to reproduce them without a license, and that Congress would need to act to create a more reliable exemption for that sort of thing. Court of Appeals decisions are only binding precedents within the corresponding regions, but they generally have persuasive force throughout the country until and unless the Supreme Court overrules them.