Runway发布GWM Worlds 2，引入WorldPrompt实现实时交

Earlier this month, world model company Runway introduced GWM Worlds 2, a research preview that “turns high-fidelity video and audio generation into real-time interactive simulation.” Runway calls this an “autoregressive diffusion” model; with autoregressive describing how it generates over time.

One new feature in particular caught our eye: WorldPrompt, a proposed input format for specifying a generated world and the actions within it. It allows you to fix some aspects of a simulated environment — including the first frame — and then create a series of timestamped events. The events, or actions, can even be prompted in real-time.

To understand the implications of WorldPrompt, we spoke to Kamil Sindi, Runway’s CTO, and Robin Kahlow, its Principal Research Scientist for generative video and multimodal AI. We also have exclusive comments from Anastasis Germanidis, co-founder & co-CEO of Runway, courtesy of a podcast swyx and Vibhu did with him.

Who’s building real-time interactive world models?

First, some context about world models that can generate interactive video and audio in real-time.

Runway is reportedly valued at $5.3 billion, based on its most recent fund raise of $315 million in February. Its first release, GWM Worlds, was launched last December.

Alongside Runway, there are several other notable projects in this domain: Google DeepMind’s Genie 3 (which also generates at 720p and 24 fps), Odyssey-2 Pro, and World Labs’ RTFM (Real-Time Frame Model). We’ve summarized their differences in the following table:

Given the complexity and massive latency demands of real-time video and audio generation (which we’ll get into below), all of the projects listed above have limitations. For instance, Google notes that Genie 3 “can currently support a few minutes of continuous interaction, rather than extended hours.”

But as our interviews with Runway show, real progress is being made.

The central idea of WorldPrompt

WorldPrompt, a new feature in GWM Worlds 2, helps differentiate Runway from its competition. You can think of it as a control layer for characters, cameras and the environment. As Kahlow put it, it’s a way to “control all the different subjects in the world” — similar to a computer game.

“Like, if there’s an NPC [Non-Player Character] somewhere, the NPC might walk up to you and say something. So you could achieve the same thing with this kind of model, where you can have very detailed control over everything in the scene.”

As the name suggests, WorldPrompt is a prompting mechanism — not a programming language. So, unlike virtual world games like Minecraft or Roblox, GWM Worlds 2 doesn’t offer scripting capabilities or the ability to control state. But there’s a power to that, as Sindi pointed out.

“You can create promptable worlds on-demand with video and audio in sync, across all these different domains and environments. That’s not a distant-future hypothetical thing,” he said.

But there are also limitations to prompting a world model. We asked how reliably the model would follow an instruction to create, for example, a law of gravity or a certain ability in a character?

“Yeah, so it’s a research preview,” Kahlow replied. “So it’s not perfect, of course, and there are still flaws. It really depends on how difficult the action is. I would say movement works quite reliably.”

Sindi added that more training plus scaling the data and models is resulting in “better following.”

How a video model becomes a real-time runtime

Despite the current limitations of GWM Worlds 2 — especially if you compare it to pre-designed and scriptable worlds like Minecraft or Roblox — the true promise of world models like Runway is that they’ll eventually lead to fully self-generated, real-time games and experiences. Which is an extremely hard engineering problem, as Kahlow reminded us.

“There are two challenges. One is making the model not generate a whole clip at once. So instead, you want it to generate frame by frame while you’re looking at it. And the other challenge is actually making the generation fast, so you can play it in real time.”

High-level view of GWM Worlds 2 process

GWM Worlds 2 offers real-time interactive worlds streamed in continuous 720p video at 24 frames per second (fps) and audio at 48,000 Hz.

Runway achieved this firstly by taking its foundational audio-video generation model and fine-tuning it to the new WorldPrompt format, so the model can follow that. It then post-trains the model to generate autoregressively.

“And after that, we work on making it real-time through distillation methods,” Kahlow added.

Co-CEO Anastasis Germanidis offered more technical details in our podcast with him. He told us that the process starts from “bidirectional diffusion that basically generates an entire video at once and [makes] it autoregressive.” This allows the model to “generate one frame or a few frames at a time.”

Autoregressive causal diffusion vs traditional video models; image via Runway

Germanidis described two possible forms of distillation in order to make it real-time: distilling a larger model into a smaller one or reducing its diffusion steps. As a general example, he said a model might go from around 50 denoising steps to four, with some quality loss but potentially comparable results.

The challenges of real-time generation

Germanidis admitted that there were issues with how it generates real-time interactive video.

“The biggest challenge with autoregressive models is error accumulation,” he said. “You’re feeding generated frames back into the model to generate the next frames, and if there are any small errors, they accumulate over time.”

Errors compound; image via Runway

Sindi told us there are also challenges dealing with “infinite generations” of content.

“There’s all these challenges around what context to keep, what to discard that’s not important. And so there’s all these optimizations we have to think about, so we’re not blowing up our GPU memory.”

Another current limitation is long-term memory. “The model does not have perfect memory,” Kahlow said. “That’s still an open research problem.”

Causality and correctness

While performance is the primary challenge for Runway at this time, its world model also has to produce plausible consequences when a user takes different actions.

Germanidis used the example of simulating football; he pointed out that online video training data contains more successful goals than failed goal attempts, so a video model might render the first more convincingly.

“If I take this action versus this action, you want it to generate equally realistic outcomes,” he told us. “That’s, I think, the big gap between video models and world models: that idea of counterfactual generation.”

Image via Runway

Sindi told us that evaluation gets harder the more complex interactions get.

“If you have this multi-prompt, multi-character, multi-scene [environment], how do you really understand what was causal and what was not?”

To try and solve that, Runway has some automated verifiable tests. But since GWM Worlds 2 is a research preview, Kahlow noted that doing tests yourself is also advisable — “trying out your model to see what doesn’t work is really important.”

More than gaming — there are agent use cases too

Gaming is the obvious use case for what Runway is building, but there are others. Kahlow mentioned robotics — for example using a simulated environment to test how a robot works.

Another, more intriguing, use case is to use it to test agents at scale.

“Having thousands of simulated environments is much less challenging if you have a suitable model like GWM Worlds,” Kahlow said.

But how does an agent know what’s changed in the world — is there a structured state that it can read, or is it just the generated video and audio that it’s consuming and understanding?