Bootstrapping World Models from Dynamics Models in Multimodal Foundation
  Models
Authors: name: Yifu Qiu; name: Yftah Ziser; name: Anna Korhonen; name: Shay B. Cohen; name: Edoardo M. Ponti
Published: 2025-06-06 11:50:18

Abstract: To what extent do vision-and-language foundation models possess a realistic
world model (observation times action rightarrow observation) and a
dynamics model (observation times observation rightarrow action), when
actions are expressed through language? While open-source foundation models
struggle with both, we find that fine-tuning them to acquire a dynamics model
through supervision is significantly easier than acquiring a world model. In
turn, dynamics models can be used to bootstrap world models through two main
strategies: 1) weakly supervised learning from synthetic data and 2) inference
time verification. Firstly, the dynamics model can annotate actions for
unlabelled pairs of video frame observations to expand the training data. We
further propose a new objective, where image tokens in observation pairs are
weighted by their importance, as predicted by a recognition model. Secondly,
the dynamics models can assign rewards to multiple samples of the world model
to score them, effectively guiding search at inference time. We evaluate the
world models resulting from both strategies through the task of action-centric
image editing on Aurora-Bench. Our best model achieves a performance
competitive with state-of-the-art image editing models, improving on them by a
margin of 15% on real-world subsets according to GPT4o-as-judge, and
achieving the best average human evaluation across all subsets of Aurora-Bench.