Agentic physical reasoning for world-model evaluation and refinement
Video models make clips that look right and behave wrong — a frisbee turns into a ball, a pot melts instead of breaking. VeriPhy measures what went wrong, says exactly what it was, and has the model generate again.
The order matters more than any single component. VeriPhy commits to what the video must show while it still has only the sentence, so a convincing picture never gets to negotiate the standard it will be judged against.
From the prompt alone, before any frame exists, the critic produces a list of obligations: how many objects should be present, which way each should travel, what should stay upright, what should remain legible, what should be audible and when. Because the list comes from the text, a fluent video cannot talk the critic out of it.
Each obligation goes to a frozen specialist tool, never to a general opinion. A tracker follows objects across frames, a counter counts them, a depth estimator says what is in front of what, a reader reads text on screen, a listener checks whether a promised sound occurs. None of these tools is ever asked whether the video looks good.
An obligation comes back supported, contradicted, or unknown. The third answer is what buys the other two their credibility: when the tracker loses an object, the critic abstains rather than inventing a score. Each contradiction is stored with the measurement, the time window and the rule that produced it.
The violated obligations are folded back into the prompt as explicit instructions, and the same generator runs again with the same seed and the same control inputs. No fine-tuning, no second model, no post-processing, no frame surgery. The sentence is the only variable — which is what makes the comparison at the top of this page a fair one.
One round of evaluate, rewrite, regenerate, closed end to end on Cosmos3-Nano — a generator held out from VeriPhy's development — across the 600 VideoPhy-2 test prompts. Read every number below as VeriPhy's own plausibility score: it reflects the obligations this critic checks, and nothing else.