Keybase developer here. Keybase does automatically update on Mac, and you can check if you're out of date on the CLI with `keybase update check`. Additionally, the "widget" popup from the system tray will display an out of date banner automatically.
4.2.1 was a bugfix release that only affected Linux and BSD, so we didn't push out Mac or Windows releases for it.
4.2.1 was a bugfix release that only affected Linux and BSD, so we didn't push out Mac or Windows releases for it.