Twin Rollouts: Noise-Coupled Counterfactual Branching in Interactive Video World Models

Yu Ma; Hongli Shi; Xinran Xu

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arXiv · 2608.08982

Twin Rollouts: Noise-Coupled Counterfactual Branching in Interactive Video World Models

Yu Ma·Hongli Shi·Xinran Xu

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Abstract

Interactive video world models generate rollouts autoregressively under an action stream, yet they are trained and evaluated almost exclusively on factual prediction. We study counterfactual generation inside the rollout: given a trajectory the model has itself generated, what would have happened had the actions differed from step t* onward? We formalize noise-coupled twin rollouts --- a factual and a counterfactual branch sharing the generated prefix and the future exogenous noise sequence, diverging only in the action stream at an intervention point. Because the factual branch is self-generated, its exogenous noise is known exactly: the abduction step of Pearl's counterfactual procedure is exact by construction, sidestepping the approximate-inversion problem faced by editing-based pipelines. Noise coupling further turns the minimal-change principle into a per-sample verifiable property: we define a spatiotemporal locality metric that penalizes divergence outside the causal descendants of the intervention, computable against simulator ground truth without a learned judge. Forking the simulator state at t* yields ground-truth counterfactual re-renders, which we use as verifiable rewards for post-training. This note establishes the formal framework, metric definitions, and positioning; experiments are forthcoming.

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BibTeX RIS

Yu Ma, Hongli Shi, Xinran Xu. 2026-08-10. Twin Rollouts: Noise-Coupled Counterfactual Branching in Interactive Video World Models. https://arxiv.org/abs/2608.08982

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