AI-driven NPCs are living lives and planning parties all on their own

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Rich open worlds with emergent NPC social structures aren't as far off as we thought.

AI NPCs chatting about their day.
(Image credit: Joon Sung Park et al.)

We may soon be entering a world where NPCs don't just run through lines of code, but form complex relationships with other NPCs even when we're away, or seem to, at least.

So far we've been subject to some pretty rudimentary NPC AI systems. Enemies and followers will react to their environment in real-time, making decisions based on your play style and so on, but a recent paper (PDF) by researchers at Stanford University and Google Research describes an impressive "architecture for generative agents" in open world environments. 

The paper is titled "Generative Agents: Interactive Simulacra of Human Behavior" and it goes over the clever way they've made NPCs behave in believable, spontaneous ways.

To test the capability of a generative framework they'd designed, the researchers built a little open world similar to "The Sims", as they say, though the graphics are more akin to a Stardew Valley. After adding a sprinkling of personality into the NPCs' seed data, they dropped the little agents into the world and watched them interact in impressively complex ways.

One NPC's given "intent" was to plan a Valentine's party, and plan she did. She ran around inviting her NPC friends, and spent the day before the party decorating the venue with her bestie. That friend, whose backstory included a secret crush on another character, invited her crush to the party.

Diagram of how generative agents interact throughout their day. (Image credit: Joon Sung Park et al.)

The social behaviors of spreading the word, decorating, asking each other out, arriving at the party, and interacting with each other at the party, were initiated by the agent architecture.

"The social behaviors of spreading the word, decorating, asking each other out, arriving at the party, and interacting with each other at the party, were initiated by the agent architecture," reads the paper.

Not only does the generative architecture allow the NPCs to "perceive" the environment around them, but also build up a believable understanding of their world with a "comprehensive record of the agent's experiences called the memory stream." By reflecting on their retrieved memories, and planning their actions accordingly, they can form complex relationships and coordinate large groups.

Underneath it all, the system uses a large language model—think ChatGPT—to generate the behaviors. As the paper observes, "large language models encode a wide range of human behavior represented in their training data" which can be used to narrate believable actions and conversations. And believability was the specific goal of the researchers; they aren't saying these are literally sentient agents, just characters who frequently seem real. In a sense, the characters speak their reality into existence, and are susceptible to certain errors, like making embellishments.

One of the main ethical concerns the paper notes over such "believable proxies of human behavior" is the potential for people to fall in love with the NPCs. Or as they call it: "forming parasocial relationships with generative agents even when such relationships may not be appropriate."

"Despite being aware that generative agents are computational entities, users may anthropomorphize them or attach human emotions to them," the paper warns. 

The way the researchers propose to tackle the issue is by ensuring NPCs "explicitly disclose their nature as computational entities," and for developers to ensure their designs are "value-aligned so that they do not engage in behaviors that would be inappropriate given the context, e.g., to reciprocate confessions of love."

The process of perceiving, accessing the memory stream, reflecting and planning before acting. (Image credit: Joon Sung Park et al.)
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Humans will literally pack-bond with anything, whether that be an AI that explicitly discloses its non-humanness, or an inanimate object with a face-like collection of grooves, so those measures may not help. (And believe it or not, this has already been a problem.)

I say bring on the human-AI relationships, but that's a conversation for another day.

If things continue the way they are, it looks like "emergent social dynamics" aren't too far away for game NPCs. One day you'll re-enter a village you ransacked to find mourning mothers holding funerals for their loved ones. You can bet they'll hold on to all those times you shouted "FUS" at their chickens, and they'll even have the capacity to plot revenge for their wronged avian compatriots.

While we wait, you can watch the replay of the simulation demo that accompanies the paper.

Katie Wickens
Katie Wickens
Hardware Writer

Having been obsessed with game mechanics, computers and graphics for three decades, Katie took Game Art and Design up to Masters level at uni and has been writing about digital games, tabletop games and gaming technology for over five years since. She can be found facilitating board game design workshops and optimising everything in her path.