The Mathematics Subject Classification (MSC) system deployed in both AMS and ZbMath databases has now been updated to the 2020 version! As this classification is updated every ten years, now is the ideal time to check it out and perhaps download a copy.

Here is the PDF version: https://mathscinet-ams-org.libproxy.helsinki.fi/msnhtml/msc2020.pdf (link requires UH credentials).