Probably a mix of Z systems, that stuff goes back 20-odd years, and even then older code can still run on new Z systems which is something IBM brags about.
Mainframes aren’t old they’re just niche technology, and that includes enterprise Java software.
Uh, Java is specifically supported by IBM in the Power and Z ISA, and they have both their own distribution, and guides for writing Java programs for mainframes in particular.
This shouldn’t be a surprise, because after Cobol, Java is the most enterprise language that has ever enterprised.
The amount of stupid AI scraping behavior I see even on my small websites is ridiculous, they’ll endlessly pound identical pages as fast as possible over an entire week, apparently not even checking if the contents changed. Probably some vibe coded shit that barely functions.