Apple Released Thunderbolt Firmware Update for Devices
According to iClarified site:
This update provides Thunderbolt performance and stability fixes.
When your computer restarts a gray screen will appear with a status bar to indicate the progress of the update.
Do not disturb or shut off the power on your computer during this update.
Folks if you are interested in updating the new software then you can select Software Update at top left side of the screen from Apple menu.