It clamps transients on a 6.4V nominal rail, with a breakdown voltage between 7.13V and the maximum clamp of 11.3V at the peak pulse current. The DO-201AD axial package suits through-hole board layouts where a leaded part is preferred for thermal mass or retrofitting an existing hole pattern.
The reverse standoff voltage of 6.4V is the maximum DC or AC peak voltage the diode will not conduct under normal operation — your rail should stay below this. The 1500W peak pulse rating assumes a 1 ms pulse width; derate for longer pulses per the datasheet curve.
onsemi has marked the 1N6268ARL4 as Obsolete. If a last-time-buy window has closed, a parametric match within the Mosorb family or a comparable TVS from another brand may be needed — confirm the standoff voltage, package, and peak pulse power before substituting.