All but one release of Mac OS X (now macOS) has been certified as Unix by The Open Group, starting with 10.5:
- 15.0 (Sequoia) on Intel Macs and on Apple Silicon Macs
- 14.0 (Sonoma) on Intel Macs and on Apple Silicon Macs
- 13.0 (Ventura) on Intel Macs and on Apple Silicon Macs
- 12.0 (Monterey) on Intel Macs and on Apple Silicon Macs
- 11.0 (Big Sur) on Intel Macs and on Apple Silicon Macs
- 10.15 (Catalina)
- 10.14 (Mojave)
- 10.13 (High Sierra)
- 10.12 (Sierra)
- 10.11 (El Capitan)
- 10.10 (Yosemite)
- 10.9 (Mavericks)
- 10.8 (Mountain Lion)
- 10.6 (Snow Leopard)
- 10.5 (Leopard)
At any given time, Apple's page on The Open Group site only lists the current version of macOS and sometimes the previous version, but all of the links above were at one point found via that page.
macOS's status as a certified Unix is called out in Apple's Unix technology brief, which also has other good technical bits in it that will help you compare it to other UNIX® and Unix-like systems.
Andrew Josey, VP Standards & Certification of the Open Group confirms that 10.7 Lion was never registered as a UNIX 03 product.
