People please let this thread die, we had 5 BootROM updates after MP51.0085.B00. This thread is totally obsolete. Hey, anyone seen this too? Started to install 10.13.4 final, via USB pendrive on my SSD and the installer asked to install a new firmware. Edit: Confirmed. New firmware on Mac App Store 10.13.4 full installer: MP51.0085.B00 No release notes or more news about what changed on the new firmware. CPU microcode still not updated for mitigation of Meltdown/Spectre. You can download the full installer on MAS and run it to just update the firmware, without reinstalling or installing High Sierra. You will need a Mac EFI supported GPU to update the firmware. Note: If you try to update the firmware with createinstallmedia pen drive, seems the installer has a bug and can't bless the firmware and shutdown the Mac Pro to kickstart the firmware update, at least on on my two Mac Pros. To be safe, run the installer on macOS to upgrade the firmware.