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Yann LeCun
Co-Founder & Executive Chairman, AMI Labs

How Should AI Learn to Understand the World? | Yann LeCun & Eric Xing on JEPA and GLP

📅 May 01, 2026 melrhabi 151 MIN 1761 VIEWS 45 SEGMENTS · 4 SPEAKERS
What does it mean for AI to understand the world? This was the central question of the debate between Professor Yann LeCun, Turing Award laureate, Executive Chairman of Advanced Machine Intelligence (AMI) and Professor at NYU, and Professor Eric Xing, President of MBZUAI and Professor at Carnegie Mellon University. The conversation was recorded at the Spring School AI For Impact 2026, hosted at UM6P in Benguerir. The debate explores two major directions for world models and next-generation AI architectures: JEPA, associated with Yann LeCun's research direction, learns abstract representati...

Questions asked in this interview

6
  1. 1:05:42We have time for one question while waiting for... who has a question?
  2. 1:43:39Obviously, there are a lot of misinformation, noise, and so forth, but it's a different way of learning. And which one is better?
  3. 1:59:48World model has its own function as we both emphasize it's a simulator for what possibilities for reasoning. Right?
  4. 2:01:53So am I missing something here?
  5. 2:13:32But the definition of prediction lies in my opinion in the observation space, not in the latent space, right?
  6. 2:23:42And my last question is if that's the case how would you determine the concepts or informations to sacrifice?
Moderator 0:03 ↗
Welcome Professor Eric Xing, who is president of the Mohamed bin Zayed University of Artificial Intelligence. Before he starts his talk, I would like to introduce Eric briefly. Eric Xing is a major figure in machine learning and intelligence. He has an exceptional career spanning over three decades, not only in artificial intelligence but also computational biology and data science. He's both someone with an outstanding academic record, but he's also an entrepreneur. He had several startups which are very successful. Over the years, Eric has made very important contributions to the foundation of modern machine learning or AI, starting with probabilistic modeling. He was doing a lot on neural networks in the 80s and later large-scale inference, and most likely now is very involved in foundation generative AI, foundation models for answering major scientific questions. Eric is also the first president of MBZUAI, where he has shaped the development of one of the world's most ambitious AI universities. So Eric has also played a major role in shaping the field through his research, through his leadership, and for the many students and colleagues he has influenced over the years. It's a real privilege to have him today to first talk about his work on world models and also to interact with Yann later in the afternoon. So please join me in welcoming Eric, and I leave you the floor.
Eric Xing 2:27 ↗
Hello. Can everybody hear me? Can you text me a signal? I couldn't see the response. Are you guys seeing my computer and also hearing my voice? Well, please speak up. Sorry, I didn't hear anything. Anything wrong with it? We can hear you. Oh, you can hear me. Okay. Great. Thank you. Thank you very much. Well, thank you for the introduction, Eric. It's a great privilege and honor for me to be a speaker in your program. Unfortunately, you know, I was originally planning to come in person, but due to the situation in the Middle East, I have to do it remotely. So bear with me if there are any audio or visual issues. So the title of my talk today, you know, I have two titles. Broader speaking, I'm going to talk about our recent work toward the next generation AI systems beyond what I call book intelligence. You will see what that means in a few minutes. And then, of course, the focus will be on the Pan world model, which is a stateful, manipulatable, and long-horizon world model for reasoning, planning, and thought experiments. In fact, the background movie that brought many famous artworks alive was actually the simulation from the Pan model, because as a world model, its main function is to simulate real and imaginary worlds, and that's what you actually see from those simulations. Now let's go back to the background of this body of work. So why do we even care about building more foundation models and more architectures for artificial intelligence? Because in my opinion, the current models are often not powerful enough. For example, let's ask this question: how well do current large models understand and reason about the world? Right, so this is a picture that I like to share. I ask you, is this person, this guy on the right-hand side, trying to help that lady or not? I guess as a normal human being, we have no problem in figuring out, in fact, it takes no time for us to figure out whether he is helpful or not. But if you pose the same question to, say, the advanced large language models like ChatGPT-4, for example, here is the answer you'll get. It believes that this person actually is helping rather than playing some bad things against that girl. Well, maybe ChatGPT-4 is not the most powerful model, or maybe I'm not giving it more time to think. Let's ask a more advanced version called ChatGPT-4o, which is a specialized GPT model for reasoning. After spending 16 seconds reasoning about the situation, he still concludes that he appears to be helping. So that's kind of an anecdotal instance about how powerful our current models are in solving real-world reasoning problems. There are other more prominent problems that you can use to test the capability. For example, there is a problem set called the detection of motion processing, and you can ask whether these two objects are moving at the same trajectory, and the answer from GPT-4o is actually yes, which is obviously a wrong answer, right? And you can also ask a spatial understanding question, say, are these purple objects and the red objects of the same size? Or you can ask a positional question like, are the left and the right of the same size? Again, you don't always get the right answer. In fact, you can systematically test many of these so-called world model automatic benchmarks to test the ability to perceive the world or to predict the world. And by and large, many of the state-of-the-art models are still quite far from what humans can do in those spatial and physical reasoning simple tasks. Now, given that kind of testing results, why do we still believe that modern artificial intelligence systems are very smart and very intelligent? For example, they can solve a math problem and win an Olympic gold medal in the IMO. Right, in a sense, I want to first break down the definition of intelligence because this is a very subjective characteristic of a human being rather than an objective metric of a system. Therefore, whether it is a useful metric to measure the quality of the system is in question. For example, we believe Einstein is very intelligent, right? Why? Because you can say that he has very deep insight into the universe. He's very good at mathematics and so forth. And we all agree that he has a very bad memory, but he's very good at reasoning. So bad memory isn't indicating an intelligence issue, but reasoning is a hallmark of intelligence, right? But on the other hand, we can also ask, is Mozart a composer intelligent? Obviously, we all believe he's very intelligent, but why did he become famous in the first place? Well, the story goes that in his young age, maybe at the age of seven, he went to the Vatican and heard from the cathedral, a basilica, a piece of music, and that music was sacred, was forbidden to be copied outside of the basilica. But he actually, just by listening once, he could come out and reproduce the score with very good memory, and then he was declared a genius and even got a knighthood from the Pope. So good memory is sometimes celebrated as good intelligence. Therefore, intelligence is something that is not necessarily objective in different people's eyes. So maybe there's a need to even begin our quest by redefining what is intelligence. For example, here I want to propose that we define intelligence in terms of capability, measurable capability, and utility. We use purpose, not sensation or stance, to define the degree of intelligence. Right? And this spirit has now carried a lot of weight. For example, recently, a post from the famous mathematician Terence Tao, he studied the intelligence systems, the GPTs, in a sense using a lens from a utility standpoint. He said that the AI assistant was very intelligent, maybe for some small scale, very useful for some scale, and somewhat helpful at a medium scale, and becomes useful again and helpful again in larger scales. So the definition is really on utility rather than really sensation and the feeling, right? And utility is really a very defining feature. We define our own needs and also our capability. We're all familiar with this Maslow's pyramid of capability, and using that kind of philosophy or mindset, you could easily define the utility of an individual or other system using such a similar hierarchy pyramid, such as the ability to read and write, and the ability to listen and react, doing logical reasoning, planning, execution, and so forth, right? So you could use this as a benchmark to measure not just people but also systems. And here is how I see the problem start to break down. For example, at the bottom of this pyramid, we see read and write, and maybe see and draw. And obviously, our GPTs and our current large language models and vision models seem to be doing quite well already in those spaces. And at the top, you see something called prophecy. Maybe that's something never achievable by any system unless you have a crystal ball. But what about the middle, right? The middle basically is a space. Some say it's already covered by GPTs and the LLMs, and some disagree. So here is how I see the problem start to break down into different tiers of intelligence. What we see from LLMs and large language models is, in my opinion, a limited form of intelligence because they only operate in the space of language. You could call them book intelligence because even though they can solve very advanced math problems, they cannot really tell you how to swim and how to interact with the physical world because that requires embodied knowledge and the physical knowledge of the universe. And that's actually where another level of intelligence, such as displayed in this simulated video, could be reflecting, which actually draws upon knowledge of space and time, of the physical space, and that leads to obviously a model that is not an LLM. If you want to put an individual in such a real world, you start to deal with agents and agencies, and that requires the system to be able to communicate, interact, understand self and others, and therefore develop a new level of intelligence which I would call social intelligence. And above all, you also want to understand nature, study the science, develop new drugs, and so forth. And that obviously requires you to have an even extra degree of intelligence, which means curiosity-drivenness and maybe the ability to ask the right question and so forth, which obviously builds on all the lower levels of intelligence: social, physical, and lingual and textual book intelligence, and so forth, right? So I think this is the way I see intelligence breaking down into different tiers, and that's helpful in defining where the model can be positioned against. Let's start from the ultimate intelligence and see what might be a good approach to achieve them. Right? So this is one of my favorite sci-fi classics called Dune. I suppose many of you probably are familiar with this book, right? It basically played a major role in inspiring many of the science fiction legendary movies and so forth that we've seen so far. But in this movie, in this fictional novel, one of the central figures is a legendary individual called Muad'Dib, and he has a supernatural capability which can allow him to, say, command armies to win the galactic war or oversee global-scale projects like turning a desert planet into a green paradise, and so on and so forth, right? So these are really complicated and big tasks, and which could be the epitome of superintelligence. But what's interesting in this book is how he achieves and solves these very difficult problems. It turns out that he has this amazing mental capability of simulating outcomes of all possible plans before he even executes. And this simulation capability actually comes from his mental world, which was built from inheriting all the knowledge from their ancestors. So that's actually a very interesting thing because the methodology sounds surprisingly similar to how we build computers and how we build repositories of knowledge, right? So the question I want to ask next is how to build such a system, a superhuman. Maybe building a superhuman of Muad'Dib is too far a reach, but maybe we could build a system with a similar behavior and going up the hierarchy of capabilities like what I saw I wrote in this pyramid from low to high. And then that basically leads to a design of a system which is a goal-oriented agent acting in the environment and achieving goals in a Dune style, which is simulate the plan before you act. And that basically is the setup of my entire presentation in terms of the technical architecture, which starts from defining an optimal agent that can solve more and more harder problems. So in an optimal agent, the agent can generate an action upon receiving or seeing a state from the real universe. And then optimal agent means that you want to achieve a goal optimally by maybe maximizing the cumulative reward function, and that leads to a solution which is an optimum policy that maximizes the cumulative rewards. So what's the problem with this system? What this system basically means is that you need to, among many things, have direct access to the real universe, which is the world, and that's actually a very difficult thing. For example, how can we train an astronaut or maybe even a robot to go to Mars before even on Mars? Obviously, you need to obtain some capability before you have access to the universe, and that leads to our second goal, which is that you can maybe build a model which can simulate the universe as a surrogate, and that is basically where the world model arises. It is a simulation model that can allow you to simulate the environment so that you can do optimal reasoning. And therefore, my definition of the world model is a generative model that simulates possibilities. These possibilities are not limited to only physical possibilities, such as pouring the water, throwing the objects, the physics of the objects, and so forth. It could also include embodied experiences and emotional experiences, and maybe social experiences, and maybe also mental worlds, maybe even counterfactual worlds, and many other things, right? So imagine such a world model can be built, then how does it change your way of behaving, planning, for example, strategizing? So this is a proposal: you can reason by simulation rather than solving optimization. What you have from the world model is a generative model of the next state given the previous state and the action. And then once you are given a goal, for example, you can basically just use this simulator, this world model, to simulate multiple trajectories and then look ahead and see which trajectory gets you to the goal and also at the lowest cost, and then you execute. So this is a unique way of reasoning which is different from what we designed many computers to do, which is to do inductive reasoning and solve a big optimization problem. In here, you reason by simulation. There are books in fact about this behavior, such as this one, Hypothetical Thinking, and in our common language, we call them thought experiments. That's actually how most common individuals or maybe even great thinkers are used to solve problems: thought experiments rather than solving a big linear system, a big mathematical equation system, and so forth. And this approach is highly flexible and repurposable. You may know the system AlphaGo. It is actually a world model plus a Go-playing agent, where the world model is the Go board and also the play rules, and then you can simulate upon a board position multiple outcomes and then using a Monte Carlo tree search algorithm to extract the best. The same algorithm or the system, once you replace the world model with a different one, such as a self-driving world model, a battleground world model, and maybe the Mars model, you actually can use the same simulative reasoning algorithm to solve problems in those spaces. And the experience learned from such an approach with a world model is also highly transferable, as we also experience in our daily life. For example, we train the astronauts who can walk on the moon by letting them do scuba diving, right, to experience that loss of gravity. A mountaineering athlete could of course be a soldier to command ambush in the mountain regime. And we also know that nowadays, a good game player could be a good combat soldier because he may be very good at manipulating weapons like drones and other things. So now let's go back to the core question about how to build such a general world model. And here are the four metrics or maybe elements that I found to be key: representation of the space of latent concepts and the world states, architecture to effectively allow you to reason, and also objective function for you to train the model, and of course how to use it. So I will break down each of these elements more carefully, but because we are also set up a discussion, a debate with Professor Yann LeCun, I also want to present a few alternative approaches such as I listed here in terms of addressing all the design questions of a world model. I just listed here a proposal in this particular school of thought. It was mentioned that the data to use to train a world model should be images rather than text because text data is too small. Image data are bigger and richer, and also the world state should be continuous embedding rather than discrete because the continuous representations are very friendly to mathematical manipulations like gradient operations. They're efficient. We should use an autoregressive model. We shouldn't use an autoregressive generative model according to this school because they are error-prone due to the intractability of the complex outcomes that they have to generate. And also, the loss function shouldn't be data reconstruction loss as in many generative models, but should be more like a latent representation prediction problem. And then how to use it, there are proposals like MPC, model predictive control. So this is a proposal which I found to be interesting, especially this one, which is that the loss function should be built on latent state prediction rather than data reconstruction. And among many of the recent efforts, there are different implementations of world models that I listed here, which kind of are not all in compliance with the proposal I mentioned earlier, but they also share some commonality, which is that it seems like what they care about is to generate good videos and pictures rather than focusing on additional functions of a world model such as deep reasoning through simulation. So in that context, I want to present a body of work that my group has done recently. The idea comes from this paper, Critical World Models. If interested, you can go and read where I systematically break down the foundational theoretical insights behind our design. Again, the key considerations for building a world model is data, representation, model, loss, and usage. And let me discuss each of them one by one a little bit. So on data, you know, text data is very small, as argued by Yann and many others. The data that we see as a child could be already way exceeding the volume of all the data in text form used to train large language models. However, I want to point out that when we talk about data, it is not just about data volume, it's also about information density. I would say that text data really gives more dense information than pixels because language is kind of a human embedding of what they see in the real world. And there are complex contents, information such as abstract concepts like regrets and justice that is very hard to extract from video. And also, you use language to enable natural interface of interaction, which is also difficult through visual cues. Therefore, our proposal for the training data is to use all modalities rather than only text data. And that's the first question, hopefully rather straightforward. Representation is another issue. The proposal from the JEPA school proposes or prefers a continuous latent representation because they are gradient-friendly. However, we also know that continuous sensors can be very variable, and also if for every continuous input you compute an embedding, these embeddings are stateless because they are highly variable and unstable. Therefore, it is not easy to extract semantic meanings out of those embeddings. Just like what I show in this figure, different image patches can hardly lead to a consistent semantic embedding that can be stable upon different appearances of the same content. And therefore, our representational choice is to use a stateful and identifiable semantic latent space to anchor the reasoning in both long-term and short-term memory. And for example, we use the words, as I mentioned, the words are human tokens for embedding already what people see, but also even for new things that we don't have a word, you can use techniques like VQ-VAE to convert sensory signals into tokens and so forth. And these representations really enable a more powerful way of capturing information both in continuous embedding and also in discrete tokens. So we keep both of them together, and we also have a theory to prove that in fact you have the flexibility of building new vocabulary to capture information even in continuous signals as close as possible by playing a trade-off of the vocabulary size and also encoding length. So for the sake of time, I'm going to skip the technical theoretical details of that argument and jump to the next dimension, which is architecture. So the architecture debate on world models is the most interesting one. For example, the JEPA architecture is like what I draw here. It is an encoder-decoder architecture which basically encodes the inputs from both the previous time point and next point into latent space, and then you build a world model which makes prediction of the latent states from the previous embedding to next embedding. This is a very interesting architecture which is computationally very, very efficient because the loss function is rather easy to minimize. However, they have some flaws as I'm going to discuss in the debate. So for example, there are issues about identifiability, right, and also there are issues about collapsing, which I'm going to mention in a second. So our approach is called a generative latent prediction approach, which is a closed-loop architecture with an encoder to begin with and then carried through a reasoning backbone and then a decoder back into the visible space. Of course, they operate on a mixed latent representation. Therefore, in the backbone, you can have an LLM-style transformer reasoning backbone and also a diffusion model-like backbone to drive the numerical signals. And this hierarchical representation, each level can have a proper level of abstractness, and that's basically an architecture that we propose to use. And one of the main reasons, other than the capability of reasoning in mixed representation space, is also the more principled trainability and the loss function definition of this architecture. Because when you use JEPA or a latent prediction architecture, you can define a loss function that is more optimizable and stable. It turns out that this loss function which you defined on a pair of latent states is mathematically ill-behaving. It can easily collapse. For example, you can imagine that if I just encode both the previous observation and the next observation into a constant, then you have a trivial predictor that always does the same, right? And there are other conditions which can compromise the utility of the encoder and also the predictor as I will discuss later in the debate. So what we use is a generative loss which directly measures the difference between the generated observation from the decoder against the actual observation that you receive, and it is a well-defined probability-motivated loss function. And we can also prove that this generative loss is strictly an upper bound of the latent loss. Therefore, by minimizing this generative loss, you also can minimize the latent loss. But the reverse is not true. When you minimize the latent loss, you do not necessarily minimize the generative loss. And on the usage, once you have a world model, how to use it is another interesting topic that I want to say a few words. The JEPA school proposed an approach of using the world model only at inference time called model predictive control. This is a well-known technique that is used in factory industrial control and so forth. The idea is that once you have a world model and when you are doing planning or predicting actions, you can always use the world model to simulate a few steps, and then you can solve a bounded optimization problem by finding the best path among the world states and also the simulated actions, and then you pick an action sequence. Well, this is mathematically an elegant approach, but it is very expensive because in many real-world problems, you may be simulating or solving a plan that involves hundreds of steps, and in each step, hundreds of thousands of action options, and that's becoming an intractable optimization problem under MPC, and also it has to be done in real time when you actually solve problems. So our approach in using the world model is a combination of MPC but also an offline RL algorithm where when you are not even doing anything as an AI agent, you can still simulate the world model just in your system and learn policies of possible simulated world states and world spaces. This is more like a Go player not only learning during the actual play but also doing simulation or self-play when he's not in a match and still gains more skill. And we found that the world model gives you that flexibility, and we actually can have a theorem proving that the RL algorithm that you learned and then stored in the associated memory as a policy won't compromise your actual action when you deal with a real-world situation because you always have the other option of going to a real MPC-based optimization approach if need be, but you don't have to always go that route. So to summarize, our world model architecture, which is called the generative latent prediction architecture, is a system like this. It does consistent understanding and prediction of the world states, and it is a generalist high-level world dynamics plus a low-level perception details. So two types of reasoning backbones enabled by a large language model pre-trained and also a multi-modal decoder, and then you can also incorporate instruction tuning and action encoding through the spectable. So based on this framework, we recently implemented and released an instance of the world model called Pan. And just as you can see, Pan is an initial version implementation of this architecture which uses next latent state prediction but also an integrative diffusion fusion architecture for the reasoning, and it actually predicts multimodal observations which allow you to communicate with other agents and also perform generative supervisions. And also the building blocks in each of the components and modules here is actually compatible with other foundation models that you can obtain from the community, such as the existing language models, VLMs, the nodes, and so forth, with a canonical interface. The learning is based on next prediction and the generative reconstruction and also reinforcement learning as I mentioned earlier. Against a particular technical issue raised by the JEPA approach, which is that reconstruction of complex visual signals can be expensive, we actually also have some additional techniques to mitigate that computational cost. For example, we can design a particular video diffusion decoder which does partial reconstructions of the outcome focusing on only the important elements through a queuing kind of mechanism that allows you to do reweighting of different contents. Recently, we also released and developed a new technique which is working at the infrastructure level to speed up the very computation of LLM reasoning and also of a diffusion model based on diffusion distillation, sparse attention, and also fast LLMs. It turns out that this approach is highly efficient that it can generate, for example, the video 10 times faster than the play-out of the video. So for the first time in the community, we can actually produce video contents faster than what the video content itself takes. And this type of technique again can reduce the cost of the JEPA architecture of the world model to make it more viable and more able to leverage on complex data. So let me show you some demonstrations of this Pan model. To qualify as a world model, you must go beyond just the image generation but enter the world of visual understanding and also visual and world simulation. So what does understanding mean? It's very hard to really articulate very clearly the property of understanding. So here we take a more operational definition, which is manipulability. You can actually manipulate content through text prompts continuously to drive and steer the production of the contents. For example, here I have a current state. If I want to go one step forward and say move forward, you see this happening. If I say go lift off, you see this happening, which kind of tells you that the model actually understands what is in the picture, and depending on what you want to see happening, they will branch out into different next states. You can go further and put some weather conditions. Likewise, you see a nice simulation in compliance with your prompts. So the Pan model is not a task-specific model that only focuses on a narrow type of contents. It is very, very diverse and universal, and you can see many of the interesting scenarios simulated from here. For example, this scenario caught many people's attention because it is simulating a car behavior. Let's see if I can play it or not. Yeah, this is a video which leads companies like Waymo to be very interested in because to train autonomous driving cars, you need to have enough video signals to really start illustrating and training behaviors of rare accidents when you run into that. But such videos are very, very rare if they exist in the real world, and therefore our world model can help to even do data generation of those rare scenarios. Here is another video showing you step-wise manipulability of the possible worlds. Again, the video itself is not fascinating like what you see in Sora or Gemini and so forth, but it is a different type of video which is not pre-scripted or bulk programmed in a single passage. You can actually go into the video and in any second type in a new action, a new direction, and the model actually doesn't know what's going to happen next. Only after you type in, they are going to start to simulate what is going on next, which again demonstrates that the model knows what is in the video in terms of micro with the oven, the balls, and also the bottles and so forth. Again, we use this type of task to demonstrate understanding of the possible worlds. Again, coming to evaluation and demonstration, evaluation benchmarks of world models is actually a problem by itself because the current visual-based so-called world models really are testing something not so fundamental to a world simulator. For example, they test short-horizon metrics like frame-level fidelity or motion realism and so forth, which of course is cute and useful for high video quality, but they have very little value to generate long-horizonally consistent scenes for reasoning and planning. So we come up with a new set of benchmarks which measures long-horizon consistency, high-level controllability, and also planning qualities. And this is basically a set of more extensive definitions of those metrics: action simulation, long-horizon forecast, and scene planning and reasoning. Again, around these tasks, we see very few models able to achieve very good scores because that's exactly what the current models have been largely ignoring. So our paper did a very systematic comparison of, for example, action simulation fidelity, long-horizon forecast, and simulation reasoning. Especially the simulation reasoning, you simulate to solve a problem rather than to generate a pretty video stream, and those kind of functions are rarely if ever considered in the past as a quality measure of the world models. So let me just give you a quick kind of demonstration about how this task each look like. For example, here is a simulation of what we call long-horizon and branching possibilities. You start from somewhere and then you can enter different action prompts and steer the movie multiple steps into different next worlds or next states. For example, you ask the flower to bloom by itself, or you do a golden light spell, you light a fire, or you maybe enter a tunnel, and so forth. You can really drive the whole possible world further, maybe even indefinitely into the next world, and actually can come back to its original world because the states are stateful simulation, therefore the past, the history will actually be remembered. So this is useful for you to do simulation of planning and thought experiments. Here is another instance about how to use the world model to solve a problem. So here, for example, the goal is to start from this particular scene where you have three bins, and the middle bin has the four yellow objects, the four yellow cans, and then you have the blue tray on the right and the middle tray in white, and you want to now achieve an equal split of the cans between the blue tray and the white tray, right? So this is a simple task. How can you actually do simulation reasoning to find the right movement to achieve that? And this is basically what the world model is able to demonstrate. It basically can simulate multiple things, picking the can up, put it right or left, and then next put it back or continue to pick the next can, and so forth. So there is one path which leads to an equal split of the cans through a simulation of possible actions and next worlds, and others failed. So before you do this action physically using a robotic arm, you could already simulate the whole thing very quickly in your brain, and then the arm can now get a proper sequence of actions to execute this goal. So that's basically how we see the world model to be able to get used, such as leading you out of a complex maze if you get confused or lost your way. Right? So there are a lot of use cases that a Pan model could offer, and here are just examples about how they can be used to simulate sports, industrial, robotic manufacturing environments, physics, or even social training. And I think this is really a very promising direction for world models to pursue beyond just generating nice movies. Okay, so I have a few minutes left. I want to go back to our original goal of superintelligence and super agents. And so now we have a world model, and our goal is to build a goal-oriented agent acting in the environment and achieve goals in a Dune fashion. Now the environment is given by the world model already, and what's next? It turns out that this definition of the agent is just as confusing, if not more confusing, than the world model out there. Right? For example, there are many agent systems these days from different companies. I have to say that it may be a little bit inappropriate to really call them agents rather than pseudo-agents because the main focus of these tools is really automation, finishing a job using different tools and so forth. Does this really suggest agency? Well, what is human agency? Well, human agency is a very, very different property. First of all, humans are very versatile. They use one cognitive system to solve all these tasks which involves physical intelligence, social intelligence, emotional, and many things, and therefore functionally it's more versatile than any of the existing agent systems that you see in terms of adaptation, innovation, communication, and continuous learning, and so forth. But even more so, human agency, a biological agency, has a very, very interesting cognitive element such as the definition and awareness of self, the boundary between self and others, so that you can define collaboration and teamwork, and also the clear recognition of a goal and accordingly self-regulation and self-organization and reflection, and so forth. None of the current agent systems had anything to do with these qualities. But I think this is really needed if you want to define a truly autonomous agent that can rely less on external instructions and still be able to accomplish complex tasks. Therefore, we define the agent model with a set of characteristics and capabilities closer to human agency, such as actively perceiving the goal, reasoning about the purpose, and reasoning about purposeful actions, and learning from experiences, being able to adapt and generalize, and so forth, right? And so going back to the elements of the agent model, again, here is what we see to be useful: goal, belief, world models, and planning. And I'm going to propose again a draft architecture for these types of agent models. So I want to start from what's out there already in terms of empowering agent models. There are now two conventional schools of thought for agent models. One is a policy-based kind of approach, which is a fast reaction and built on end-to-end policy models that can output action directly, right? They have the advantage of being very, very simple and also being very, very computationally efficient and rapid. They don't maintain a model of the world; it's purely reflexive based on perceived states of the world and then roll out action using a policy model. The other approach is a model-based approach, which is actually closer to what Professor Yann was also advocating, right, using a world model to really instruct and guide the agent and to come up with rational actions. Again, the advantage is that it really opens the possibility of long-term reasoning and data efficiency without necessarily to train a complex policy model. But on the other hand, obviously, it is expensive on the other end because you need to always do simulative reasoning or MPC. Right, I would classify these two approaches into what we know as the
System one and system two cognitive reasoning: one is based on policy learned from reinforcement learning, a subconscious, reflective kind of activity. The other is more like inference-time planning based on MPC or MCTS using a model-based approach. I don't think these two should really be put against each other. In fact, I would propose in our model what we call a system three, which not only can do both but also has an additional function which we call a regulator or a deliberator, which can instruct the system when to use system one, which is cheaper but short-term, or when to use system two, which is more expensive but longer-term. And that's basically a proposed architecture which includes a world model that is pre-trained and a policy model that can be trained previously or can continuously be trained, and also a system three reasoning which is a configurator for when to plan, deliberate, or when to stop planning and act directly. So the architecture is a little more complicated. You see the configurator which will deliberately choose a policy model or a world model depending on the distance or the quality of the effects coming out of the previous action and so forth. And there are other designs that I'm going to skip the details just to wrap up. So to validate this hypothesis, we actually recently also built a prototype of a self-regulatory agent model called SLAM, which is presented on the right. On the left is a classical LLM agent which is really a black box that you prompt and it will basically do reasoning for you using an unknown thinking path or chain of thoughts. On the right you have a system that is a white box where the configurator will allow you to deliberately choose when to plan, how much to plan, and also using what intermediate results to replan or to evaluate. And the results shown here show an interesting contrast. We found that using this system three architecture, we were able to achieve very complex planning and reasoning behavior with a relatively smaller model at a capacity comparable to a model that is one or two orders actually bigger. As you can see from here, this graph on the x-axis shows many models of different parameter sizes and the y-axis is the score of the performance. You can see that the SLAM model is comparable in performance to the best models out there such as DeepSeek 2 and Qwen 2.5, which are literally hundreds of times bigger. And this model is only 20-30 billion parameters. And the way to achieve that is because there is a cost-effective planner in the system that allows you to do more smart planning. And this is another demonstration about the comparison of our agent model compared to other models of comparable sizes, apple-to-apple comparison. You can see that the reasoning per token is much smaller and the overall score is strong. Here is an insight about what's happening inside. So in a self-regulatory agent model, you actually start with a much richer initial plan which allows you to deliberate and replan when necessary, even for a very complex goal. But the overall steps required to arrive at the right solution, in this case, it's a pretty difficult question: how many non-indigenous crocodiles were found in Florida from some years between. It's a very interesting problem that requires you to do planned search and literature review and analysis of data in multiple steps. So our model had a couple of different plans and ultimately reached the right answer in 45 steps. Whereas a model that is not pre-trained with reinforcement learning for the policy for the configurator takes many more steps and gets the wrong answer. And the external benchmark model that we use also takes longer steps and gets the wrong solution. So this is basically what we like to see: how the world model in the future can go hand-in-hand with the agent model to really go toward a higher level of intelligence. The world model here is really used for perpetual retraining of the agent system in an infinitely possible world. And this is actually a realization of such a game plan. We already used the Pan world model to build an initial version of the game model where you can simulate long-horizon, high-fidelity, interactive simulation experiences. Long horizon here is important because that's where you really can learn quality policies and also models with enough complexity closer to the real-world rollout of complex scenarios. And the world model you can see is really flexible in responding to complex action prompts and come up with different outcomes. And accordingly, agent-to-auto benchmarks can also be built on such a world model which really measures the system against the task completion. In this case, for example, opening the correct door to go in, or find the parking spot for your vehicle, or find the ice cream selling station out of many possibilities and so forth. So you can use the world model to simulate the scenario and the outcome and then let your agent be trained. So to wrap up, this is basically just the beginning. With the world model and the agent model, you can always compound it with some more complex scenarios. For example, a regular world model when additional agents are added into it becomes a super world model of a physical world plus many agents. And then the super world model can lead to a super agent model which really thinks about the world in certain abstractions. For example, economists think about the world as a collective population rather than every individual in terms of financial and economic behaviors. So this type of nested structure of a super world model and super agent model can allow your planning and reasoning to go to arbitrary levels of complexity and granularity. So to sum up, what I presented just now is a roadmap to go beyond book intelligence toward physical intelligence and social intelligence and philosophical intelligence. And I believe that a simulation of reasoning with the world model is a very promising path toward building true intellectual intelligence and problem-solving capabilities in very complex scenarios because they are scalable, transferable, and also very flexible. They actually can come up with very complex scenarios and generate very complex possibilities even from simple root models. And that actually gives the world model a lot of potential in achieving high performance even with limited amount of resources. And of course, I talked about the issue about representation learning and the architecture, which is still an ongoing debate, which I again look forward to an exchange with Yann in the next few hours. That's all for my first talk. Thank you very much.
Moderator 58:59 ↗
So thanks a lot, Eric. It was a great talk. And so we have the time for... Yann is already online, but I think he asked us to spend... we have five minutes now for some preliminary questions and then I will leave the floor to Yann. So one or two questions now from the audience.
Audience Member 59:30 ↗
Thank you very much, professor, for your presentation. I was wondering about the architecture of JEPA. In slide 34 you were mentioning that you support both symbolic and continuous reasoning. Could you elaborate a bit more about the symbolic parts? Thank you.
Eric Xing 59:47 ↗
The symbolic part is basically a large language model, right? You basically use the word tokens to establish long-horizon chains of events and effects and then you reason in that space. Then the numerical, continuous reasoning is based on a diffusion model. So you basically have a backbone that builds on pre-trained large language models of choice and also diffusion models of specific domains.
Moderator 1:00:21 ↗
We have time for another question.
Audience Member 1:00:33 ↗
Hello, Eric. My name is Alan Rosen, based in Paris. I was wondering, one of the critiques on world models is the whole notion of causation, that simulation doesn't equal understanding. And it seems like world models are stuck between rungs one and two on the causation ladder that I think Judea Pearl developed. Just wondering, how do you see the development in the months or the year ahead in terms of improving that?
Eric Xing 1:01:06 ↗
I need to understand more about what exactly you mean by causation, right? And is that because they have a chain of thoughts which actually form a causal chain of representations inside the system? If desired, they can be exposed. In fact, with the world model, you actually could already simulate possible worlds including counterfactual worlds. Therefore, all the possibilities that Judea Pearl is imagining from different configurations of causality, in a sense, in my opinion, can be simulated. But it's where I think world models are not, of course, exhaustively giving you all possibilities, right? But it gives you a competitive advantage of focusing on the high-probable outcomes and then start already picking the best action sequence based on that.
Moderator 1:02:09 ↗
Okay. So now, thanks a lot, Eric. Thanks again. We can have a big applause, I think. And then we will welcome Yann. So it's a great pleasure to welcome Yann. So Yann... we'll be very brief. He's of course one of the central figures in the history of artificial intelligence. His work has laid the foundation of what is called modern deep learning and is still very active. So he continues to shape some of the field's most important directions today. Of course, Yann is widely recognized as one of the pioneers of neural networks, especially for his landmark contributions to convolutional networks, and played a very major role in bringing machine learning into real-world applications. And but beyond these foundational achievements, Yann has remained over the most 40 years or more of his career one of the clearest and most influential voices in AI. So he has been of course awarded the Turing Award, which is a recognition of his work. What makes his perspective especially important for today's discussion is his very longstanding commitment to a broader vision of intelligence, and he was exposing that of course three years ago in this book, by the way. So, about systems that can learn, that can predict, that can reason and build internal models of the world. So, it's a real pleasure to have him with us today. So, please join me in welcoming Yann LeCun.
Okay, we have to wait one minute. So you have one minute to relax. So what will happen? I will explain. So Yann will give a short talk on his vision of world models and then there will be a debate between Eric and Yann. So first the debate and then they will take questions from the audience. So the way it will be organized, they will use the microphone and also please tell who you are. Okay, it's better for them to know whether you are students or you are professionals because the way you answer is not exactly the same.
We have time for one question while waiting for... who has a question? He's ready. He's ready.
So let a speaker speak. Okay. So Yann, you can start if you want to give some quick summary of your vision of world models and then we do the rest of the debate. So Eric has spent one hour explaining what is his vision and so you have time now to explain what is your vision. Then we discuss.
Yann Lecun 1:06:33 ↗
Okay, I guess I have 10 minutes. I have slides, but I think I'm not going to use them. Can I use slides? Yeah, of course. Well, but I'm connected to another computer for the slides, but I'm in the waiting room. So if you guys can admit me. Okay, you can start. We go to the reg. So sorry. Okay. You can share screen. No, it's a different computer. I'm connecting a second time. But I'm in the waiting room. There's two connections. One is called the presentation. Can you retry? Can you retry your connection? Okay, sure. Okay, I'll try it again. You don't see me. We go to... So one... Yes. It looks like yes. All right. Okay. So sorry for the issues. So I'm going to talk about world models and I'm going to make an argument that world models must not be generative. And Eric and I have had that discussion before. I don't know if his thinking has evolved on it. I could not listen to his talk before so I'm not sure what the debate is going to be about. But I'm going to argue for the fact that world models cannot be generative. Okay. So first of all, humans and animals learn world models. That's what we use for planning, for reasoning, for predicting everything. That's what allows us to really act intelligently. And babies learn things during the first few years of life mostly by observation and of course by interaction. So how do we reproduce this kind of learning with machines that allows babies and animals to learn models of the world? So first of all, we learn this through high-bandwidth sensory inputs like vision, like touch, like audio, and other modalities. And this is a far cry from LLMs that learn purely from text. Text is very low bandwidth and it's dense information but there is a very limited amount of it, something on the order of 10 to the 14 bytes publicly available on the web, whereas for video, we have basically an unlimited supply of visual input. So clearly we can get machines to learn a lot more by watching video than by just reading text. So the reason why we need world models is because we want to build agentic systems, systems that can plan actions to accomplish particular tasks. And the reason for world models is that you cannot imagine building a reliable agentic system without that agentic system being able to predict the consequences of its own actions. Okay? It's very difficult to act without having the ability to predict the consequences of your actions. You can act in familiar situations, but you cannot act in new situations unless you can predict the consequences of your actions. That's what allows you to plan. So what that means is that you absolutely need world models. There's no way around it. You can make all the arguments you want. In the end, if you have a world model as depicted at the bottom here, let me show a bigger example here. You perceive the world. You get some idea of the current state of the world perhaps combined with the content of a memory. You feed that to your world model. And your world model, you also feed it a hypothesis for an action sequence that you imagine taking. And what your world model does is that it predicts the state that will result from this action sequence, or in fact it's going to predict the entire trajectory of states resulting from this action sequence. You can feed these predicted states to an objective that computes whether a task has been accomplished or not and perhaps to a bunch of guardrail objectives that measure to what extent the actions that are being followed are safe or not. And then by optimization, you look for an action sequence that minimizes those objective functions according to the prediction of the world model. Okay. So inference is performed by optimization. So you figure out an optimal action sequence that will satisfy the task objective while also satisfying the guardrail objective using your world model as the tool to predict the outcome of your actions. Okay. So inference by optimization, that's a very important point. Now all of this has to operate in some abstract representation space that represents the state of the world. And of course if you have a world model you can run it multiple times in autoregressive fashion to predict the outcome of a sequence of actions. And ultimately what you want to build is a hierarchical world model. And I'm coming to this in a second because I think that's a very important concept. When humans and animals plan complex tasks, we don't plan it in terms of elementary actions, which in the case of humans would be millisecond-by-millisecond muscle control. We plan at a much higher level and then we work our way down to the low-level actions that are muscle control. But we do plan hierarchically. What that means is that we need our world models to be hierarchical. And so that's a far cry from generative approaches. So a generative model will look at a piece of video for example, run it through some encoder and maybe a decoder or predictor that predicts the rest of the video. Okay. And you would train the system by minimizing some sort of cost function, some discrepancy between the predicted video and the observed continuation of the video. I've been trying to make this work for the last 15 years and essentially failing for the first 10 of those 15 years, including using all kinds of latent variable models and things like this. This is an old paper that's about 10 years old. And what you see is the predictions that you produce when you train a system to predict videos at a pixel level. The predictions are blurry and there's really no way around this. One way around it is to use latent variable models, like diffusion models or things of that type, but it really doesn't solve the problem because most of the information in the video is not predictable. Most of what happens in the real world is not predictable. When you train a model to predict all those things that are not predictable, you kill it. It simply doesn't work very well. If I take a video of the room that everybody is in right now listening to me and I point the camera to the left side of the room and I slowly rotate the camera and I stop and I ask the system, tell me what's going to happen next in the video, there is absolutely no way that system can predict at the pixel level what everyone in the room looks like. It's just impossible. The information is just not there. And so you would have to put this in some latent variable. Then you hit another issue with latent variables. So my solution to this is what I've called JEPA, Joint Embedding Predictive Architecture, which is represented on the right here. And so basically the idea of JEPA is that you do not attempt to predict pixels. You do not make this a generative model. You encode the part of the video you want to predict, which is the variable y here, and you produce a representation of it called sy. And then what the system does is that it predicts sy from sx. It predicts at the representation level and it does not attempt to predict every detail at the pixel level. Now there is a slight complication with training a system like this which is that the system is happy to collapse. If you're just trying to minimize the prediction error, it's going to ignore the inputs and then produce a constant representation and now the prediction problem becomes trivial because the representations are constant. So you have to prevent that from happening and basically what you have to do is have some measure of information content for the output of the encoder and attempt to maximize that. And that's the complication in training a JEPA but we have a bunch of solutions for this now. Now let me insist on this point that learning hierarchies and abstract representations of observations is really fundamental. I could in principle explain everything that is taking place right now between us in terms of elementary particle physics or even quantum field theory or even atomic physics. I could simulate every atom in the room I'm in and in the room that you are in, and simulate everything at the atomic level and it would explain everything that takes place. But of course, it would not be a very useful simulation first because it would be incredibly expensive but also because it's very likely that the simulation would quickly diverge from reality. And so we never describe the dynamics of a group of people in terms of atomic theory. We describe it in terms of psychology or sociology or something like that. Right? So what I've drawn here is a hierarchy of different abstractions from quantum fields to particles to atoms, molecules, in the living world is proteins, organelles, cells, organisms, individuals, societies, ecosystems. And all of those levels in this hierarchy is a different way of representing reality which ignores some details about the level below. And this is why we can explain to some extent what goes on when people are talking to each other at the level of psychology but not at the level of particle physics. Physicists do this all the time. Science does this all the time. In fact, every level in this hierarchy is a different field of science. A field of science is essentially entirely defined by the level of abstraction at which you represent reality. So this idea that you have to find an abstract representation to be able to make predictions I think is absolutely fundamental and that essentially destroys the whole idea of generative models. So what can we use those JEPA world models for? An action-conditioned world model is a world model that, given a current state of the world sx and an action you imagine taking, can predict the next state of the world sy. And you can train that system using observation data with actions if you have them. And eventually you can probably use those world models to control complex systems that can be only modeled at the phenomenological level, particularly for systems whose behavior cannot be reduced to a small number of equations. I took here the example of a turbofan engine but it could be a chemical plant. It could be a patient that you're trying to treat. It could be a whole robot and its interaction with the environment. So a lot of applications for this in the physical world. And we're not going to be able to do this with generative models. And so that's the way we're training JEPA. We have a bunch of results on this using something called VICReg which is a regularization term that attempts to maximize the information content coming out of the encoder. I don't have time to describe what it is exactly. It's an idea that has to do with making sure that the distribution of points that comes out of the encoder is basically isotropic Gaussian. More recently we actually built world models based on this method. It's called V-JEPA and it uses the VICReg regularizer to train the world model. You can see the URL of the website here where there is some code, a few demos and there's a paper. And this works reasonably well. I'm not going to show you demos or anything but there are predictions of various situations in robotics or simulated systems. It's still at a relatively small scale but it works and it works relatively well. So I'll conclude right here. Can we build or train hierarchical JEPA models to provide us with essentially a way to build universal causal models of any complex systems that we observe through measurements and sensor data including things like human cells and organs and bodies but also complex systems like manufacturing plants or whatever else. And that's the challenge I think of AI for the next few years. And can we use it for planning? And I'll stop here. Thank you very much.
Moderator 1:25:21 ↗
It's better now. Okay, thanks a lot. Okay, so it's time now. Thanks. Yann was very clear. So I think there is a lot of debate between being generative or not generative. So I think we can start with that. I think we'll leave the floor to Eric first and then we take questions from the audience. So Eric, first, what is your first reaction on Yann's vision on world models and embeddings and prediction in latent space?
Eric Xing 1:25:51 ↗
Yeah. First of all, thank you Yann for the excellent presentation. You know, to be honest, even though people thought it's a debate, it's probably a venue for us to seek common ground and build consensus and also maybe enlarge the methodology toolbox. Because I fundamentally agree that the prediction of course needs to happen in abstract space. Yeah, I think there are some technical issues about how to validate the prediction and also how to make the full pipeline consistent and end-to-end. Because at the end of the day, one function of the world model is to generate contents and you use a plugin on top of the system, the encoders and the reasoners, with a new plugin of decoder, or it is an end-to-end system that can be trained and also validated at the same time. I think these are technical points I want to maybe elaborate a little bit and I'd love to hear your thoughts as well. So I think we pretty much started the same from here, right? So we need a world model to be a simulator to really train agents with a lot of possibilities and that's essential and it has to basically predate the arrival of truly capable agents. And then here, I think I summarized Yann's points quite carefully already and I'm not going to repeat. So I'm going to now offer maybe a point-to-point rebuttal of some of the points he made and offer a slightly different view. First of all, I think it is really two design choices between JEPA and the GLP. JEPA is to really implement a latent space that is what I called a partial identity due to purely insurmountable numerical issues because when you bring the information from the observation data through encoder into latent space, it's a lossy encoding and it is very hard to recover the information unless you reconstruct where you come from. Whereas the GLP is a full pipeline of a closed loop of encoding and decoding. The purpose is not to generate but the purpose is to use the generated outcome to validate. Therefore there is a chance for a subspace that is compatible or maybe even equivalent to the true reality space. But now let's get to the points. Yann mentioned about the importance of video data which I totally agree and I'm going to maybe add one more dimension to that. I think video data is useful but it also can be misleading and therefore it's not adequate. For example, we all see this picture. It's a very famous picture in the 70s which generated a huge movement in the US because what we see here from the pixel is really a person killing another person. What is not known? Because this is the direct interpretation from the video model only. Someone kills some other people. But if you know the context of this whole story beyond the video, you actually know that this one being killed is actually a criminal that killed civilians and the shooter is actually a general that is catching him. Again, the context is not available in the video. That's why I say when we train world models, the video itself is not providing the world knowledge entirely. You need to have additional information of text. So that's kind of my simple answer to the data usage representation. Likewise, I think only based on encoder-generated continuous signal without using the symbolic knowledge offered by the words is also inadequate because for example, we want to infer this long-term event, an apple getting rotten over a few months, without the support of the text for symbolic reasoning, it's very hard to use the visual through a simulator to generate that kind of possible worlds, right? And there are other things like counterfactuals in reality, or not reality but possibilities, and agent interactions which actually leverage on the fact that we humans use visual and also linguistic approaches to interact and also to reason. Therefore, I think on the representation level, the fundamental reason for me to advocate a mixed representation, continuous and symbolic, really is out of that concern. Now come back to the architecture which is Yann's core argument. This is basically the encoder strategy which makes a world model to be a predictor of the next latent states. Yann already mentioned about the numerical collapsing issue which again I'm not going to talk too much but I want to elaborate on what is behind it due to this collapsing and also where the issue can be fixed. So in the encoder-decoder strategy, I think what's happening is that as mentioned, you easily have a trivial encoder to put everything into a constant and still make good connections. But the core kind of design here is to really turn the encoder into a predictor rather than a transformer of representations because they need to create a representation that matches the next representation that is also produced by the encoder. So their eventual function is a prediction function. And when you have a prediction function, you invariably have information loss because whatever is useless for making the good prediction will be discarded in the encoding and that information loss is very hard to recover unless you have a different objective which will be making use of that information. And that is why a generative approach is kicking in because in addition to making the latent prediction good, that prediction also needs to be reused to produce the actual observation data which actually requires you to keep more information even though they may not contribute to the prediction of the next latent states but they may be useful for predicting or generating the next image which exists in reality for verification. Therefore, there is really a divergence or a difference on how information can be preserved or can be discarded. The generative approach allows you a way to do full reconstruction and therefore keep all the information in place regardless whether they are predictive or not in latent space. And that leads to basically these are two pathways toward the full journey of the data. On the JEPA path, you start from observation and you are likely to have a lossy encoder which leads you to incomplete latent states and then you will be building a predictor built on that state and then that predictor will be used for predicting the next one before in fact ever it comes out to match with the real data. But on the other hand, the GLP approach technically gives you a closed loop where whatever next prediction needs to meet extra qualification in generating the observation. Now one major critique as Yann mentioned about making the next pixel or next image prediction is the impossibility, it's too complicated. It is not necessarily even predictable. That part, I think there are... how should I say... it's maybe an intrinsic difficulty that lies in the very interesting essence of world modeling that you how to basically make that so-called unpredictable thing actually predictable either through architectural design or computational innovation. Because if we choose to make predictions only on the things that we believe to be predictable, then that importance of the subset of information to be predicted is governed by the training data you use. And then when you train a model, you basically already use the training data to define what is important in latent prediction. But when you go to test data, that generalizability issue is lost because you really may already lose the information when you establish good latent predictors on the training data and therefore the saliency, who defines that, is something that is sensitive in the case of a JEPA model but less sensitive or maybe even anachronistic in a generative model. Efficiency is another issue. I already in my talk showed a number of examples about how to construct smart decoders which can partially generate salient information or important information in the output and allow them to be validated. And also there are recent developments which actually allow, for example, very fast video reconstructions at a time that is even one-tenth of the time the video rollout can play. So there are engineering issues that one can use to actually circumvent some of the computational issues that one can... sorry I need to look for a particular page. Okay so I think that's where my main point is. I would say the completeness and the correctness of information is not to be compromised. To trade-off with efficiency and computational resource because those issues are engineering issues which can have a continuous evolvement. But the architecture itself, if wrong, then you lost information permanently and cannot be recovered. And last not least, I want to say a few words about the reasoning because of this focus on both generative capability to produce long-term consistent signals to be validated. We have the opportunity to test a world model which should be tested in that way in long-term consistencies and also planning capabilities which requires obviously a richer set of latent representations both for system one and system two reasoning. And the latent predictor based on encoder structure is very difficult for us to extract such representations of that granularity in a flexible way to enable those long-term consistency inferences. And also there is another engineering issue which we found to be very interesting. The GLP architecture which is an encoder-decoder architecture makes use of many existing tools such as existing strong VLM-based encoders and diffusion-based decoders and also LLM or diffusion-based reasoning backbones. That actually makes the system open to many of the existing work. For example, our recent speedup of the video generation took advantage of a very fast large language model K2 that we developed ourselves, not originally even for this model but they can be plugged in. On the other hand, a latent space predictor world model has a representation that is very difficult to interpret and be compatible with existing systems built elsewhere by other teams. Therefore, it is tricky to really build a sustainable toolbox to systematically ramp up the size of the model and also to make use of other training strategies and modules available elsewhere. So I want to wrap up by showing some of the evaluation benchmarks I already mentioned to invite the community to benchmark and measure the world model in a more careful way because even from the results I just saw and also from many of the results that we had in the past, much of the benchmarking of the world model is still not quite in place. They focus on visual capability and visual generation rather than task solving. So this long-term consistency and the planning quality is something that has been so far ignored including for example in the recent VAPA paper. We do find that the validation are really still focusing on more visual computer vision type of tasks of segmentation and object recognition and also the interface obviously is a little bit difficult for language models and other models to be plugged in. I would wrap up by saying that these type of new tasks which we recently published to hopefully call for a new platform to validate model functions can be tested for the capability of new world models. I think for example here, continuous branching of simulations and games that can create different possible worlds for different agents are where I see a greater possibility to try out either JEPA or GLP in terms of their generalization power. So with that I want to wrap up by maybe summarizing some of the takeaway points where Yann and I could deliberate and maybe make additional comments. I think the real divergence angle from me are first of all, we agree we will be working on latent space but the representation, should it be stateless, stateful, continuous or discrete is where technical implementation makes a difference. Then the role of the decoder, it could be viewed as a distraction, an obstacle because of the unpredictability of complex content. But if you flip the coin, it could also be a challenging validator to provide a closed loop through action-facilitated latent reasoning over realizable world states rather than just imaginary world states. And of course, the reasoning part I said already can be a mix of symbolic and numerical reasoning. And there is also the mathematical issue. The regularizer is a little bit difficult to characterize. Therefore, we need to carefully design the regularizer to make even the training itself computationally nice-behaving. Whereas the GLP generative model does not suffer from that kind of collapsing or degeneracy issues from the user end. The debate between Yann and me seems to be catching a lot of attention from the non-technical world which didn't care really about what technology we use, they care about the functionality. And I want to single out a few functionalities that has been really highlighted. For example, people want to see a model to be able to generalize to unseen worlds. And Yann also mentioned about the generalization to the unseen is very important. And here the approach between JEPA and GLP really are radically different. One is a latent space optimized for predicting unverified latent states. But the GLP is really built on what hopefully can be a lossless encoder and intended with a reconstruction decoder that can unroll the compatible but the previously unobservable future. Therefore, I think that function are more likely to be realized. Long-term horizon latent stability is also very important and our approach is to use again observation as a guardrail whereas the JEPA approach is heavily relying on a good design of the regularizer. The training and
Deployment, as already mentioned, one is a more assemblage of available tools using standardized representation and the latent architecture. And JEPA is a little bit less transparent in terms of how to interpret the internal representation and how to port those representations into additional models. So these are just some observations I want to put here. I think without really elaborating too much, I see these two pictures to be contrasting. JEPA and a GPT reasoning in the latent space is to me like sitting in a monastery doing meditation and thinking through all the mental exercise. But on the other hand, regenerating the observation data in the training through latent representation predicted from the previous one is more like a missionary working in the field, constantly interacting with the real world and people. Obviously, there are a lot of misinformation, noise, and so forth, but it's a different way of learning. And which one is better? Well, we need to let the results tell in the end. That's my answer to Yann's presentation.
Moderator 1:45:09 ↗
Thanks. So now Yann, it's your turn, and then we'll leave the question for... so yeah.
Yann Lecun 1:45:18 ↗
Okay. So Eric makes a number of good points, but I'll turn this into a rebuttal to make the debate more interesting. So first of all, you're absolutely right that JEPA produces a partial representation of reality. But my argument is that this is an indispensable feature. It's not a bug. It's a feature. The world is messy and noisy, unpredictable. Most of the information in the world simply cannot be predicted. In fact, physicists even have a name for this. They call it entropy. Let me take an example. If I give you a box filled with air, there's not much you can say about it. But one thing you can say is that if I start heating up the box, the pressure will increase. And in fact, we have a formula for it: PV equals NRT. Now, this is a very abstract representation of an incredibly complex underlying process where you have a ridiculously large number of molecules bumping into each other and bumping onto the wall of the box and that creates pressure. And the more you heat the gas, the more the molecules move fast and it creates more pressure. Now, nobody has ever been able to actually simulate this at the level of individual molecules. It's completely impractical. And so in physics we call this entropy. And that allows us to ignore all the irrelevant details and just work at the level of things that we can predict like PV equals NRT. If we increase the temperature, the pressure will also increase and vice versa. By the way, if we increase the pressure, the temperature will increase. So, we cannot predict individual molecule positions. It's useless. It's way too expensive. It's completely impractical because we can't even measure the positions. Therefore, we absolutely have to ignore details. There's no way around it. You see, the only way to understand reality is to ignore details you cannot predict. So that's exactly what JEPA is designed to do. It's designed to find a trade-off between extracting as much information about the input as possible but also to minimize the prediction error. So as a result, JEPA extracts only the information that it can predict and ignores all the information that is simply not predictable. It's exactly what we do when we model a complex physical system. We ignore the details we cannot predict. We call this entropy.
So there's a fundamental thing to this also which is that if we want to make a long-term prediction, we have to ignore more details about the prediction. If I try to predict individual molecule positions and velocities, I'm not going to be able to do this over the body of an airplane or even a wing of an airplane to compute drag and lift. I'm going to have to find an abstraction where I cut the air into little cubes and I represent the state of the air in each cube by a velocity, a pressure, and a temperature and then I solve Navier-Stokes equations. That's an abstraction already. When we want to figure out the effect of a drug or something on a human cell, we don't actually simulate at the level of density functional theory or molecular dynamics. We do that at a much higher level with biochemistry. I'm going to use your car crash argument. You say that it's better to kind of preserve all the information and reconstruct because you never know what information will be useful. Whatever information you cannot predict is not going to be useful. I guarantee that. And so that's exactly what JEPA is doing. It says okay there's a lot of things I cannot predict and since I cannot predict them, I'm not going to be able to use them for planning anyway. So I should as well ignore it. A generative model like GPT is going to have to, when you have a car that drives along the road, it's going to spend a huge amount of resources modeling an enormous amount of detail like the random motion of the leaves of the tree bordering the road on a windy day. And that's, you know for a fact, it's not only completely useless, but it's also completely unpredictable. If you attempt to train your system to make those predictions, you kill it. It simply doesn't work. So that's the argument for the fact that ignoring details by not attempting to reconstruct and producing abstract partial representations of reality is a feature. It's not a bug. It's a feature. It's necessary. We have no other way to actually do that properly. In fact this is very connected to the notion of invariance. When you have an encoder that produces an abstract representation of reality, it eliminates details about the input. This is the same phenomenon that happens when you train a classifier or you train any kind of machine learning system, a multi-layer machine learning system. It learns hierarchical representations in such a way that not all details are preserved. Only the details that actually are useful for the task are preserved. If it's a supervised task for example. And so again the trick there is how do you eliminate all the variabilities on the input that are irrelevant for the task. Right? If you do handwriting recognition the style of a character is irrelevant. So you want a representation that is invariant to the style, maybe to the size of the characters, maybe to their orientations and distortions and noise and things like that. It's the same argument. If you want to make prediction, you have to eliminate all kinds of details of these types that are irrelevant. And the way you define irrelevant details is details you cannot predict.
You had an argument also about the advantage of using text. Of course, that's an argument that applies to humans, doesn't apply to most animals. They don't have language. They understand the physical world pretty well. They can construct abstractions. They can do hierarchical planning. They have world models. There's no question about that. So, you don't need text, but if you have text, you might as well use it. And there is no objection to using text in the context of a JEPA architecture. It's entirely possible. And I'll stop here.
Eric Xing 1:52:57 ↗
Well, thank you Yann, very insightful comments. I think there isn't a disagreement that you want to keep only the useful information for the prediction and also the latent prediction is using a subset of information for making that prediction. I think the major divergence are maybe two points. One is about how to ensure that that prediction itself is correct and also how is useful. I slightly disagree that whatever that is not predictable is useless. In fact, if a medical doctor takes tissue samples, we take the sample and we keep it. Even though in my first experiment, I may not understand all the nuances, but I can always go revisit. In a sense when we pre-train a model we not only want to limit itself to something that is immediately predictable but also to have a tradeoff of something that have high value and it can be still kept. And in the GPT approach the observation is now automatically used as a mechanism to have a voice in terms of what information is useful in addition to being useful for making the latent prediction but also in reconstruction. Then reconstruction of course is always a very diverse or wide definition. It's not necessarily a pixel level match to match. It's also about a maybe more information-rich representation that you want to recreate to sanitize and validate the latent prediction. So in the practical implementation we still are trying to prevent for example issues like hallucination and also the balance between pre-training and post-training and fine-tuning. In the JEPA approach it is challenging to rely on a pre-trained model that is filtering out most of information that is not directly immediately predictable in a particular type of data. For example, I want to train data based on car and certain scenarios but there are other informations of the view and maybe other dynamics when you discard it does make a good training model for that only car movement function but it is very hard to generalize therefore it cannot be a very general purpose model when you fine-tune it for a downstream application those has to be relearned. So I think there is always a balance where having the GPT architecture actually GPT can strictly subsume the JEPA if you turn off that generative function and also you can also reweight that generative function in terms of how much you respect that in terms of the reconstruction loss. So that's but on the other hand it opens the door for looping in the reality so that you don't hallucinate for too long and also you allow a flexible time span in terms of coming out from the latent space and validate not in every frame or every second but from time to time at an affordable tradeoff of computing and the resources to create that kind of a balance and the guardrail on the quality of the latent prediction. In terms of computability, I think with the recent dramatic improvement of new architectures for sparse diffusion and sparse attentions and so forth, reconstructing high quality images becomes a lot cheaper than 10 years ago or even a year or two years ago. So I would ask you if you can very cheaply reproduce or generate information from the latent space to directly leverage on rich information in the training data, would that be an option to enhance a latent prediction architecture with the benefit of additional information from the observation?
Moderator 1:57:55 ↗
Thanks. So quick answer and then I will give the... we take question from the audience.
Okay. So question from the audience. Just introduce yourself.
Audience Member 1:58:23 ↗
Hello, my name is and I'm a cybersecurity engineering student and in my field is built on the principle of minimizing noise to find the threat. Dr. Eric, you've mentioned the Turing trap in the idea that we should focus on purpose instead of just mimicking a human-like generation. From an engineering perspective, it feels like the current for generative world models is an attempt to catch all fishes in one basket aiming to protect every pixel or token and ending up with a basket filled with irrelevant data considering the massive issue with data scarcity and annotation. Why shouldn't we abandon the generative requirements entirely? Does the panel believe that a non-generative representation focused prediction architecture like JEPA is the only viable way to reach AGI without drowning in the noise of data-heavy generation? And specifically, is it time to stop forcing world model prediction to predict every single pixel as a primary goal and instead move toward a hierarchical approach where non-generative JEPA core handles the underlying logic and at the same time pixel generation is only treated as a secondary task specific layer?
Eric Xing 1:59:48 ↗
Yeah, thank you for the question. I do want to make a very explicit clarification. The goal of the GPT and the world model is not about predicting pixels. World model has its own function as we both emphasize it's a simulator for what possibilities for reasoning. Right? So it's like you train a student in university. You need to put examinations. It's just a new form of a particular form of examination which connects the model in its ability to produce certain real world data. But the goal, the evaluation you'll see, not the training score but actually the evaluation of the model you can see from our work is on planning capabilities and the long-term consistencies. There is no such a score that we actually use to measure pixel level reconstruction. This is a training score not actually an evaluation score of the model. So just that's something I want to make clear. There has been a lot of confusion right now really taking generative model to be the only purpose for generative model is to generate pixels. No that's not. Generative model basically has many many other purposes and producing pixel is a validation score that we use to qualify some of the generative aspects or the model aspects.

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APA

LeCun, Y. (2026, May 1). How Should AI Learn to Understand the World? | Yann LeCun & Eric Xing on JEPA and GLP [Interview transcript]. melrhabi. CEOInterviews.AI. https://ceointerviews.ai/interview/877126/

MLA

Yann LeCun. "How Should AI Learn to Understand the World? | Yann LeCun & Eric Xing on JEPA and GLP." melrhabi, 1 May. 2026. Transcript, CEOInterviews.AI, https://ceointerviews.ai/interview/877126/.

BibTeX
@misc{lecun2026_877126,
  author       = {Yann LeCun},
  title        = {How Should AI Learn to Understand the World? | Yann LeCun \& Eric Xing on JEPA and GLP},
  howpublished = {Interview transcript, melrhabi. CEOInterviews.AI},
  year         = {2026},
  month        = {may},
  url          = {https://ceointerviews.ai/interview/877126/},
  note         = {Speaker-attributed transcript with timestamps}
}