It's convoluted. Ninth Circuit courts held APIs weren't copyrightable. The Federal Circuit (which only had jurisdiction because of the thrown out patent claims

It's convoluted. Ninth Circuit courts held APIs weren't copyrightable. The Federal Circuit (which only had jurisdiction because of the thrown out patent claims) held that they were copyrightable. The majority of SCOTUS here explicitly said they weren't deciding copyright of APIs. Instead they looked at both cases and said: "either it isn't copyrightable, but even if it is copyrightable, that this is fair use." Either way, Oracle loses. Arguing in the alternative is a common legal pattern, as is ruling on the narrowest possible ground. Generally when a circuit court makes a ruling, it's only "binding" precedent on subsidiary courts within that same circuit. The federal circuit is weird though, as it doesn't have a geographical jurisdiction, instead it has a subject matter jurisdiction. If a case has patent claims (or a few other things), an appeal gets routed there. So, effectively, APIs are copyrightable if there is a linked patent claim in the same lawsuit. Courts can certainly use the Federal Circuit ruling as "persuasive" precedent, and rule the same way, but it's not binding, and it's not settled law.