OneWM

Can World and Action Modeling Benefit Each Other under Unified Causal Training?

One causal model learns to predict the world
and act in it.

An illustrated white robot arm arranging rose and blue blocks in a sunlit studio
imagine ↔ act

Yue Su1,2,6,*Bokai Lin2,4,*Xinkai Wang2,4,*Chubin Zhang3Xiangnan Wu5Kuan Zhang3Weiyang Jin1Jiwen Yu1Yiming Li3Cewu Lu2,4Lixin Yang2,4,†Xihui Liu1,†

1 MMLab@HKU2 MVIG@SJTU3 THU4 SII5 UCAS6 IAAI* Equal contribution   † Corresponding authors

01 / THE IDEA

Prediction and control.
A two-way relationship.

A world model learns what happens when a robot acts.
A policy learns which action to take.
Can learning one help the other?

How much action is known?

World model

All-clean actions

Predict the effect of known actions.

WAMnoisy

All-noisy actions

Predict with noisy action conditions.

WAMmask

Actions masked

Predict without reading action tokens.

OneWM action conditioning
Outlined cells show the action-to-video connections. Every configuration preserves temporal causality.
WORLD → ACTION

Clean-action prediction strengthens control and generalization.

ACTION → WORLD

Learning actions improves future-video prediction.

02 / HOW IT WORKS

One architecture.
Three ways to condition.

Actions are both conditions for prediction
and targets for learning.

Two experts. One causal conversation.

Animated OneWM training pipelineA VAE encodes video frames, retaining a clean observed prefix and adding noise to future latents. Action chunks are embedded. Separate video and action experts exchange information through causal joint attention. Both experts receive the same instruction through their own text attention and feed-forward blocks. The action regime can be changed below. VIDEO EXPERTACTION EXPERT Framesclean prefix VAE+ε Q / K / V Joint attentionTEMPORALLY CAUSAL Text attention+ feed-forward Instruction ℓ Future latentsprefix retained Action chunkclean + noisy Embed Q / K / V Text attention+ feed-forward Action chunkcondition + target

Know the beginning. Learn the rest.

A clean prefix conditions future-video prediction and denoising of the remaining action suffix.

A₁A₂A₃A₄
Clean conditionNoisy denoising target
The observed video stays clean. Both experts read the same instruction through their own text attention.

03 / IN THE REAL WORLD

From imagining
to doing.

Precise placement. Careful alignment.
Everyday manipulation, on a real robot.

01

Build, one block at a time.

02

Find the perfect fit.

03

A little breakfast ritual.

Full robot recordings · Original speed · Silent

04 / IMAGINED FUTURES

An action.
And the world it changes.

Watch how the predicted future follows a sequence of actions.

Same actions, two futures. Drag to rotate the recorded trajectory; scrub to follow the motion.

About the videos and actions +

Each clip starts with an observed frame, followed by eight predictions. Reference video and conditioning actions come from the same sample. The 3D path shows recorded end-effector positions in metres; it is not a predicted path. Action values are raw controller commands, not displacements in metres. Sample details include timing and model information.

05 / A NEW FINDING

Dream, act, repeat.

Give OneWM an initial observation and a task. It predicts the next actions, imagines their consequences, then uses its own predicted view to decide what to do next.

An Endless Dream

After the first observation, OneWM sees only what it imagines.

OneWM · LIBERO

An imagined journey

Round 01 / 16
Initial observation · held
0.0 / 25.6 s
  1. Predict the next actions

    32 controls from the current view.

  2. Imagine their effect

    8 future frames, guided by those actions.

  3. Use the last imagined frame

    Feed it back. The next round begins.

Unified causal training connects policy and world prediction: OneWM can carry a task forward inside a world it generates itself.

About this finding

Selected task:

16 rounds · 512 predicted actions · 25.6 s in imagination

Each LIBERO example starts from one dual-camera observation and a task instruction. The same OneWM checkpoint alternates action prediction and action-conditioned video prediction. Every later visual input is its own last generated frame; no later recorded observations or recorded actions enter the loop.

The animation reveals each saved 32-action prediction in temporal order, then plays its corresponding eight future frames. The 3D path accumulates the predicted translation commands within each round; it is a relative control path, not a measured end-effector trajectory. Values use the experiment’s denormalized actions. The pauses illustrate the loop, not inference speed.

All six examples retain the full 16 rounds. This experiment evaluates imagined task progression. Simulator execution and automatic completion detection are outside this experiment; long rollouts can show drift and generation artifacts.

06 / WHAT WE FIND

Better at both.

Matched comparisons support reciprocal benefits.

WORLD → ACTION

Policy success

vs. WAMmask
94.95%LIBERO +2.50 pp
59.27%LIBERO-Plus +5.90 pp
36.68%RoboCasa365 +8.36 pp
ACTION → WORLD

Better PSNR, SSIM & LPIPS

Across all three benchmarks, against the same-architecture world model.
A closer look at the numbers +

Real-world success: 48.9% → 66.7%, WAMmask → OneWM. Three tasks; 15 trials per task and model.

World prediction, PSNR ↑: LIBERO 22.33 → 22.95 · LIBERO-Plus 20.54 → 21.05 · RoboCasa365 24.72 → 25.21. Same MoT architecture, WM → OneWM.

Selected paper results. Distributional metrics and individual perturbation categories show a more nuanced picture.

✳

Understanding the world
by learning to act in it.

Explore the architecture, experiments, and findings in the paper.

Read the paper
Paper details

Can World and Action Modeling Benefit Each Other under Unified Causal Training?

Yue Su, Bokai Lin, Xinkai Wang, Chubin Zhang, Xiangnan Wu, Kuan Zhang, Weiyang Jin, Jiwen Yu, Yiming Li, Cewu Lu, Lixin Yang, Xihui Liu.