Title: Cosmos-Eval: Towards Explainable Evaluation of Physics and Semantics in Text-to-Video Models
Primary area: foundation or frontier models, including LLMs
Keywords: Cosmos-Eval, Explainable Evaluation

Abstract: Recent text-to-video (T2V) models have achieved impressive visual fidelity, yet they remain prone to failures in two critical dimensions: adhering to prompt semantics and respecting physical commonsense. Existing benchmarks, including VideoPhy and VideoPhy-2, formalize these axes but provide only scalar scores, leaving model errors unexplained and hindering reliable evaluation. To address this, we present Cosmos-Eval, an explainable evaluation framework that jointly assesses semantic adherence and physical consistency. Cosmos-Eval produces fine-grained 5-point scores with natural-language rationales, leveraging the physically grounded ontology of Cosmos-Reason1 and an LLM-based rationale refinement pipeline. This enables precise identification of semantic mismatches and violations of physical laws, such as floating objects or momentum inconsistencies. Experiments on VideoPhy-2 show that Cosmos-Eval matches state-of-the-art auto-evaluators in score alignment (Pearson 0.46 vs. 0.43 for semantics; Q-Kappa 0.33 vs. 0.33 for physics) while also delivering state-of-the-art rationale quality (e.g., best BERTScore F1 and BLEU-4 on both SA and PC). Beyond this benchmark, our framework generalizes to other evaluation suites, establishing a unified paradigm for explainable physics-and-semantics reasoning in T2V evaluation and enabling safer, more reliable model development.