As you'll probably know, this case began in 2010 when Oracle, which had just taken over Sun, sued Google for patent infringement. The patent parts were quickly tossed out and what remained was what referred to as a "sideshow" to the main event: a question about whether APIs could be covered by copyright. Pretty much all historical evidence, including an important Supreme Court ruling from the 1990s, said no, interfaces are not covered by copyright.
Oracle and friends then spent the next decade deliberately gaslighting basically everyone who doesn't understand what an API is, and insisting that it's the same as executable code. The district court, under Judge William Alsup, who somewhat famously taught himself Java to better understand the issues in the case (he already knew how to code and was a hobbyist programmer), correctly found that APIs are not subject to copyright as they represent a "system or method of operation" which is explicitly not covered by copyright, as per Section 102(b) of the Copyright Act.
Rather than go to the 9th Circuit (as it should have) the case went to the Federal Circuit, which hears all patent appeals. That was because the case began as a patent case, even though it no longer was. CAFC judges are somewhat infamous for never finding a patent issue they couldn't screw up, and decided to extend that to copyright. In the ruling overturning the lower court, they made it clear that because they were code illiterate they could not understand the difference between executing code and an API, even though it's like the difference between a novel and a dictionary.
The case went back to the district court, where the jury this time sided with Google, this time saying that the use of the code was covered under fair use. That whole trial was a little weird, because reading between the lines, you could see that nearly all the arguments for why copying an API was fair use were really about why an API shouldn't be covered by copyright at all (as per Alsup's original ruling) and then squeezing that square peg into the round hole of fair use to make it work. Once again, however, CAFC got flummoxed by an API looking like code and overturned -- which is quite crazy because CAFC had, in its first ruling, insisted that the jury should decide this issue (as a matter of fact) and then when the jury said "fair use" CAFC suddenly decided that it was a matter of law that it could overrule.
Finally, we get to the Supreme Court. From oral arguments, it wasn't clear where the court was leaning -- with some good questions and some crazy questions. But with today's ruling, it's clear that the smarter questioners won out. The majority opinion was written by Justice Breyer, who has always been the best Justice on copyright issues, and had the support of Justices Roberts, Kagan, Gorsuch, Kavanaugh, and Sotomayor.
This is a HUGE WIN for software development, and this decade plus long fight is finally over. Mike Masnick with some good analysis on what went down today, including some tidbits from the decision.
SCOTUS sides with Google, ruling that copying APIs are fair use