Grim Reaper's Sprint/Fallout 76

Grim Reaper's Sprint is a perk in Fallout 3, Fallout: New Vegas, Fallout 4, and Fallout 76.

Fallout 3
Landing a killing blow in V.A.T.S. will immediately restore all Action Points allowing the player to begin a new series of attacks immediately. However, foes killed by allies or other means will not trigger the perk, even if in V.A.T.S.

Fallout: New Vegas
In Fallout: New Vegas, the perk only gives back 20 AP upon a kill in V.A.T.S. Although this is a significant reduction to the effectiveness of the perk, the perk is still very useful with high power, low AP cost weapons. The effectiveness of Grim Reaper's Sprint is dependent upon three things: AP cost of the weapon, damage of the weapon, and toughness of the enemy.

The following perks and traits compliment Grim Reaper's Sprint: Fast Shot, Kamikaze, Action Boy, Math Wrath, and Better Criticals.

Fallout 4
Grim Reaper's Sprint restores all action points upon a kill like in Fallout 3, but only has a 15% chance of doing so at the first rank. The second rank raises the chance to 25%, and the third rank increases it to 35% in addition to filling your critical meter completely.

Fallout 76
in Fallout 76 The chance of restoring the Action Points is based on the level of the Perk Card Any kill in V.A.T.S has a 15% chance to restore all Action Points. (Level 1) Any kill in V.A.T.S has a 25% chance to restore all Action Points. (Level 2) Any kill in V.A.T.S has a 35% chance to restore all Action Points. (Level 3)

Behind the scenes
The perk is a winner of Bethesda Softworks's Fallout anniversary contest, submitted by Marc-Andre Deslongchamps.