Fallout 4 might as well be the most combat-oriented game in the series. Unlike its predecessors, it is almost impossible to finish it without killing anybody; and the only reason we use the term "almost" is because somebody managed to do so.
Kyle Hinckley has managed to finish Fallout 4 with straight zeroes across his combat stats. He had to pour tens of hours into different characters in different playthroughs before he was able to find the right combination of skills and stats and make all the right decisions in order to finish the game with no blood on his hands.
The trick to it is, Hinckley had to find creative ways to make his enemies die without having the game attributing their deaths to him. "It’s not about whether or not I’m against violence, because the game doesn’t give you like Fallout: New Vegas-esque abilities to avoid violence completely," he explained in a vlog. "All that matters to us is [that the game doesn’t count any kills.]...Robots, turrets, legendary enemies, synths, all this shit. Zeroes. All the way down the line."
"My version of pacifism isn’t really diplomatic, it’s more exploitative of the game mechanics to achieve a zero-kill record. In other [Fallout] games, you had a lot of alternatives for bypassing the combat, whether it was with sneaking, speech checks, or a back door opened with lockpicking and hacking."
Hinckley started off easily by trapping roaches in locked rooms and kiting enemies into other NPCs who'd distract or kill them for him. However, he had to get cleverer as he journeyed deeper into the wasteland. At one point, Hinckley had to pickpocket an NPC's pocket in order to give the NPC better gear so that he'd be able to defeat a certain enemy.
In the end, the whole endeavor turned out to be a test of patience as Hinckley made his way to the finish line the long way around. To level up, he had to spend hours building the same structure over and over in order to farm its tiny XP gain. He also had to save before every dice roll and reload if the outcome wasn't favorable. The final boss fight alone took more than 5 hours of retrying as Hinckley lured the boss through mines to reduce his health then froze him with a cryo mine so that other enemies in the room had a chance to kill him.