Answer
For buying and support decisions, use the IBM i release name and version when checking hardware compatibility, PTF planning, software certification, and support dates.
IBM i Operating System and Version Management
What is the AS400 operating system called today?
The modern operating system name is IBM i. AS400 operating system searches usually refer to the same lineage that started as OS/400, later became i5/OS, and is now IBM i on IBM Power hardware.