@mitchconner @dcc I believe this is the installer script; https://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/distrib/miniroot/install.sub?rev=1.1266&content-type=text/plain

Please observe the following lines;
# Ensure that fw_update is run on reboot.
echo "/usr/sbin/fw_update" >>/mnt/etc/rc.firsttime

Please also observe the fw_update man page; https://man.openbsd.org/fw_update
>-a Install or update firmware [sic] for all drivers. It is an error to specify this option with any driver arguments. This is enabled by default unless drivers, files or -d are specified.