UNIX 2003 is not the latest version of the certification, the latest UNIX certification is (somewhat confusingly) named UNIX V7 (different thing from the classic Bell Labs V7 UNIX), but thus far only Oracle Solaris is certified to that.
z/OS is still only UNIX 95 – https://www.opengroup.org/openbrand/register/brand3601.htm – maybe one day IBM will upgrade that to the newer UNIX 98, UNIX 03, or UNIX V7 certifications, although I suspect not. IBM has decided to focus on running Linux Docker containers under z/OS instead (which it calls zCX).
UNIX 2003 is not the latest version of the certification, the latest UNIX certification is (somewhat confusingly) named UNIX V7 (different thing from the classic Bell Labs V7 UNIX), but thus far only Oracle Solaris is certified to that.
z/OS is still only UNIX 95 – https://www.opengroup.org/openbrand/register/brand3601.htm – maybe one day IBM will upgrade that to the newer UNIX 98, UNIX 03, or UNIX V7 certifications, although I suspect not. IBM has decided to focus on running Linux Docker containers under z/OS instead (which it calls zCX).