The reverse standoff voltage of 8V is the maximum continuous DC the device can sit across without conducting leakage — pick this to match your supply voltage with margin. When a surge hits, the clamp triggers at 8.89V breakdown and holds the peak at 13.6V while shunting 36.7A of 10/1000µs pulse current. That 500W peak pulse rating is the energy envelope; a sustained overvoltage above the clamp voltage will exceed it and cook the die.
Package and temperature — mounting and environment
Microchip lists this part as Active.