Apple/macOS silently removed from official Unix registry

Apple's macOS was removed from the official Unix registry by The Open Group, a non-profit organization that maintains the Unix certification program. The decision was made due to macOS not conforming to the X/Open Single UNIX Specification (XPG4) and the Single UNIX Specification (SUS). The Open Group requires operating systems to meet these specifications to be considered a certified Unix system. Apple has not commented on the removal.