Okay thanks, unexpected but good to know (at >340MB I would have expected a complete base system at least). Do you know if there is some up to date OpenBSD live CD somewhere?
At >340MB it does indeed have a complete base system. You just have to install it somewhere first :)
I don't know of any up-to-date prebuilt live CD/USB images, but I do know of guides to create them from another OpenBSD install (e.g. one in a VM): https://www.alti.at/knowhow/obsdlivecd/