'World Models,' an old idea in AI, mount a comeback
50 comments
·September 2, 2025AnotherGoodName
smokel
You probably know this, but things heavily depend on the type of board game you are trying to solve.
In Go, for instance, it does not help much to look 50 moves ahead. The complexity is way too high for this to be feasible, and determining who's ahead is far from trivial. It's in these situations where modern AI (reinforcement learning, deep neural networks) helps tremendously.
Also note that nobody said that using AI is easy.
AnotherGoodName
Alphago (and stockfish that another commenter mentioned) still has to search ahead using a world model. The AI training just helps with the heuristics for pruning and evaluation of that search.
The big fundamental blocker to a generic ‘can play any game’ ai is the manual implementation of the world model. If you read the alphago paper you’ll see ‘we started with nothing but an implementation of the game rules’. That’s the part we’re missing. It’s done by humans.
moyix
Note that MuZero did better than AlphaGo, without access to preprogrammed rules: https://en.wikipedia.org/wiki/MuZero
smokel
Implementing a world model seems to be mostly solved by LLMs. Finding one that can be evaluated fast enough to actually solve games is extremely hard, for humans and AI alike.
daxfohl
Yeah, I can't even get them to retain a simple state. I've tried having them run a maze, but instead of giving them the whole maze up front, I have them move one step at a time, tell them which directions are open from that square and ask for the next move, etc.
After a few moves they get hopelessly lost and just start wandering back and forth in a loop. Even when I prompt them explicitly to serialize a state representation of the maze after each step, and even if I prune the old context so they don't get tripped up on old state representations, they still get flustered and corrupt the state or lose track of things eventually.
They get the concept: if I explain the challenge and ask to write a program to solve such a maze step-by-step like that, they can do that successfully first-try! But maintaining it internally, they still seem to struggle.
nomadpenguin
There are specialized architectures (the Tolman-Eichenbaum Machine)* that are able to complete this kind of task. Interestingly, once trained, their activations look strikingly similar to place and grid cells in real brains. The team were also able to show (in a separate paper) that the TEM is mathematically equivalent to a transformer.
* https://www.sciencedirect.com/science/article/pii/S009286742...
warrenm
>I've tried having them run a maze, but instead of giving them the whole maze up front, I have them move one step at a time, tell them which directions are open from that square and ask for the next move, etc.
Presuming these are 'typical' mazes (like you find in a garden or local corn field in late fall), why not have the bot run the known-correct solving algorithm (or its mirror)?
daxfohl
Like I said, they can implement the algorithm to solve it, but when forced to maintain the state themselves, either internally or explicitly in the context, they are unable to do so and get lost.
Similarly if you ask to write a Sudoku solver, they have no problem. And if you ask an online model to solve a sudoku, it'll write a sudoku solver in the background and use that to solve it. But (at least the last time I tried, a year ago), if you ask to solve step-by-step using pure reasoning without writing a program, they start spewing out all kinds of nonsense (but humorously cheat: they'll still spit out the correct answer at the end).
coeneedell
IIRC the rules system for magic the gathering: Arena is generated by a sort of compiler fed the rules. You might not even need a modern coding assistant to build out something reasonable in a DSL that is perfect, then have people (or an LLM after fine tuning) transforms rule books into the DSL.
Crespyl
They have an interesting write up here: https://magic.wizards.com/en/news/mtg-arena/on-whiteboards-n...
There's a lisp variant involved, and IIRC even a parser that reads the card text to auto-generate the rules code for most of the cards.
deepsquirrelnet
> I’ve tried throwing masses of game state data at latest models in pytorch. Unusable. It Makes really dumb moves. In fact one big issue is that it often suggests invalid moves and the best way to avoid this is to implement the board game logic in full to validate it.
It sounds like you need RL. You could try setting up some reward functions with evaluators. I’m not sure what your architecture is, but something to try.
bubblyworld
Something to consider is that while it's really hard to implement a decent NN-based algorithm like AlphaZero for your game, you get the benefit that model checkpoints give you a range of skill levels to play against as you train it.
Handicapping traditional tree search produces really terrible results, imo. It's common for weak chess engines to be weak for stupid reasons (they just hang pieces, make random unnatural moves, miss blatant threats etc). Playing weak versions of Leela chess really "feels" like a (bad) human opponent by contrast.
Maybe the juice isn't worth the squeeze. It's definitely a ton of work to get right.
robertlagrant
How does this experience translate to non-turn based games? Alphastar presumably is doing something other than searching all the possible moves. Why would whatever it does not translate to turn-based?
red75prime
It would be nice if you could train a decent model on a $1000 (or so) budget, but for now it seems unlikely.
GaggiX
>This is how chess engines work
All strongest chess engine have at least one neural network to evaluate positions, including Stockfish, and this impact the searching window.
>how all good turn based game ai works
That's not really true, just think of Go.
skywhopper
??? Chess engines and Go engines have as a baseline a world model of the state of the game and what moves are legal.
GaggiX
>Fwiw nothing beats ‘implement the game logic in full (huge amounts of work) and with pruning on some heuristics look 50 moves ahead’. This is how chess engines work and how all good turn based game ai works.
Just read the parent comment.
Animats
Important subject, useless article.
Some new ideas in world models are beginning to work. Using Gaussian splatting as a world model has had some recent success.[1] It's a representation that's somewhat tolerant of areas where there's not enough information. Some of the systems that generate video from images work this way.
ryukoposting
A footnote in the GPT-5 announcement was that you can now give OpenAI's API a context-free grammar that the LLM must follow. One way of thinking about this feature is that it's a user-defined world model. You could tell the model "the sky is" => "blue" for example.
Obviously you can't actually use this feature as a true world model. There's just too much stuff you have to codify, and basing such a system on tokens is inherently limiting.
The basic principle sounds like what we're looking for, though: a strict automata or rule set that steers the model's output reliably and provably. Perhaps a similar kind of thing that operates on neurons, rather than tokens? Hmm.
nxobject
> There's just too much stuff you have to codify, and basing such a system on tokens is inherently limiting.
As a complete amateur who works in embedded: I imagine the restriction to a linear, ordered input stream is fundamentally limiting as well, even with the use of attention layers.
gavmor
I suspect something more akin to a LoRA and/or circuit tracing will help us keep track of the truth.
lsy
A world model itself, in its particulars, isn't as important as the tacit understanding that the "world model" is necessarily incomplete and subordinate to the world itself, that there are sensory inputs from the world that would indicate you should adjust your world model, and the capacity and commitment to adjust that model in a way that maintains a level of coherence. With those things you don't need a complex model, you could start with a very simple but flexible model that would be adjusted over time by the system.
But I don't think we have a hint of a proposal for how to incorporate even the first part of that into our current systems.
dejongh
This is a very interesting article. The concept "run an experiment in your head and predict the outcome" is a capability that AIs must have to attain some kind of general intelligence. Anyway, read the article, it's great.
BariumBlue
> When researchers attempt(opens a new tab) to recover [something like] a coherent computational representation of an Othello game board they instead find [bags of heuristics]
Humans don't exactly have a full representation of board space in their head either. Notably, chess masters and amateurs can memorize completely random board positions as well as the other. I'd think neither could memorize 64 chess pieces in random positions on a board.
AIPedant
That's not what "coherent computational representation" means in this context. It means being able to reliably apply the rules of Othello / chess / etc to the current state of the board. Any competent amateur can do this without studying thousands of board positions - in fact you can do it just from the written rules, without ever having seen a game - they have a causal, non-heuristic understanding of the rules. LLMs have much more trouble: they don't learn how knights move, they learn how white knights move when they're in position d5, then in position g4, etc etc, a "bag of heuristics."
Notably this is also true for MuZero, though at that scale the heuristics become "dense" enough that an apparent causal understanding seems to emerge. But it is quite brittle: my favorite example involves the arcade game Breakout, where MuZero can attain superhuman performance on Level 1 and still be unable to do Level 2. Healthy human children are not like this - they figure out "the trick" in Level 1 and quickly generalize.
mym1990
For whatever its worth, I bet the chess master would be able to instantly identify that it is a random/invalid board position, aka an invalid world state. I think the experiment you are alluding to gave both groups a very limited amount of time to look at the board. Given enough time, both groups would definitely be able to memorize 64 pieces on a board.
aurelwu
I do think even the most amateur of amateurs would be able to recognize instantly that a chess board with 64 pieces on it is a invalid game state.
yellow_postit
Not mentioning Fei-Fei Li and her startup explicitly focused on world models is an interesting choice by the author.
mingtianzhang
I used to work on a idea that instead of modelling the whole world, you can build your own Solipsistic model: https://openreview.net/pdf?id=fPaGSuQRP1O
srush
A recent tutorial video from one of the authors featured in this article:
Evaluating AI's World Models (https://www.youtube.com/watch?v=hguIUmMsvA4)
Goes into details about several of the challenges discussed.
chongli
A little bit disappointed that there was no mention of the Frame Problem [1], a major challenge with world models. The issue arises when you're building an AI agent with the ability to move through and act in the real world, updating its world model as it does so.
The challenge comes from the problem of finding a set of axioms that tell you how to make predictions about what changes a particular action will cause in the world. Naively, we might suppose that the laws of physics would be suitable axioms but this immediately turns out to be computationally intractable. So then we're stuck trying to find a set of heuristics, as alluded to in the article.
Without being a neuroscientist, I think it's likely that at least some of the axioms of our own world models (as human beings) are built into the structure of our brains, rather than being knowledge that we learn as we grow up. We know, for example, that our visual systems have a great deal of built-in assumptions about the way light works and how objects appear under different lighting conditions, a fact revealed to us by optical illusions such as the checker shadow illusion [2]. Building a complete set of heuristics such as this does not sound impossible, just somewhat obscure and unexplored as an engineering problem, and does not seem to be related whatsoever to currently popular means of building and training AI models.
jonbaer
"You’re carrying around in your head a model of how the world works" (or so you thought) ... the real AI is in a) how fast you can realize it's changed and b) how fast you can adapt. This bit isn't being optimized, it's being dragged out.
red75prime
> This bit isn't being optimized, it's being dragged out.
Of course, it is being optimized. People are working on increasing the sample efficiency. A simple search on Google Scholar will confirm it.
nathan_douglas
I'm sure neural networks are a great tool here, but I don't know how the training would proceed effectively off "mere data"; too much of the data we have is incomplete, inaccurate, or outright fantasy or misinformation or out of the ordinary.
I could see this being the domain of fleets of robots, many different styles, compositions, materials, etc. Send ten robots in to survey a room - drones, crawlers, dogs, rollers, etc - they'll bang against things, knock things off shelves, illuminate corners, etc. The aggregate of their observations is the useful output, kinda like networked toddlers.
And yeah, unfortunately, sometimes this means you just need to send a swarm of robots to attack a city bus... or a bank... to "learn how things work." Or an internment camp. Don't get upset, guy, we're building a world model.
Anybody wanna give me VC money to work on this?
ACCount37
When you're training an AI, that "mere data" adds up. Random error averages out, getting closer to zero with every data point. Systematic error leaks information about the system that keeps making the error.
A Harry Potter book doesn't ruin an AI's world model by contaminating reality with fantasy. It gives it valuable data points on human culture and imagination and fiction tropes and commercially successful creative works. All of which is a part of the broader "reality" the AI is trying to grasp the shape of as it learns from the vast unstructured dataset.
nathan_douglas
You're absolutely correct, of course. I was musing during down time in a meeting and turned it into a joke instead of engaging my faculties :)
multjoy
The AI learns nothing from Harry Potter other than the statistical likelihood of one token appearing after another.
The AI is trying to grasp nothing.
ACCount37
Any sufficiently advanced statistical model is a world model.
If you think that what your own brain doing isn't fancy statistics plugged into a prediction engine, I have some news for you.
I’ve been working on board game ai lately.
Fwiw nothing beats ‘implement the game logic in full (huge amounts of work) and with pruning on some heuristics look 50 moves ahead’. This is how chess engines work and how all good turn based game ai works.
I’ve tried throwing masses of game state data at latest models in pytorch. Unusable. It Makes really dumb moves. In fact one big issue is that it often suggests invalid moves and the best way to avoid this is to implement the board game logic in full to validate it. At which point, why don’t i just do the above scan ahead X moves since i have to do the hard parts of manually building the world model anyway?
One area where current ai is helping is on the heuristics themselves for evaluating best moves when scanning ahead. You can input various game states and whether the player won the game or not in the end to train the values of the heuristics. You still need to implement the world model and look ahead to use those heuristics though! When you hear of neural networks being used for go or chess this is where they are used. You still need to build the world model and brute force scan ahead.
One path i do want to try more: In theory coding assistants should be able to read rulebooks and dynamically generate code to represent those rules. If you can do that part the rest should be easy. Ie. it could be possible to throw rulebooks at ai and it play the game. It would generate a world model from the rulebook via coding assistants and scan ahead more moves than humanly possible using that world model, evaluating to some heuristics that would need to be trained through trial and error.
Of course coding assistants aren’t at a point where you can throw rulebooks at them to generate an internal representation of game states. I should know. I just spent weeks building the game model even with a coding assistant.