Patrick and others commited amd64 Intel cpu microcode update code over the last few days. The approach isn't perfect, but it is good enough for a start. I want to explain the situation.
When you fw_update, you'll get the firmware files. Upon a reboot, it will attempt to update the microcode on your cpus. Maybe there isn't a new microcode. Maybe your BIOS has a copy of the microcode and installs it before booting OpenBSD. This firmware installation is done a little late. Doing it better will require some work in the bootblocks to find the firmware files, but time is a bit short to do that right now. The branch-target-cache flushing features added in new microcode are not being used yet. There is more code which has to be written, but again other work is happening first. Also, Intel is saying their new microcodes sucks and people should wait a little. "Hi, my name is Intel and I'm an cheating speculator".
