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arXiv · 2610.12407

LeWAM: A JEPA World Action Model with Diffusion-Steering-Based MPC

Shashank Hegde·Alexander Popov·Elie Aljalbout·Nikolai Smolyanskiy
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Abstract

World action models (WAMs) predict actions and future observations, typically from a reconstruction-based representation that carries noisy, redundant information which can complicate downstream predictions. We introduce LeWAM, a bidirectional transformer for forward, backward, inverse dynamics and policy prediction, on a decoder-free JEPA latent trained end-to-end through all four modes. We see the following benefits: 1) Alignment: linear probes read robot and object state from LeWAM's latent better than from a regular Le World Model (a forward-only JEPA world model), while the latent ignores visual distractors as well as LeWM does and far better than a reconstruction-based WAM. 2) Acting: Closed-loop evaluations of LeWAM match a regular flow-matching policy trained on the same encoder at matched size, while also providing a world model. 3) Planning: Sampling raw actions when planning with WAMs lets MPC exploit dynamics-model inaccuracies; planning in the noise space of the policy head instead improves the closed-loop performance of these WAMs.

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Shashank Hegde, Alexander Popov, Elie Aljalbout, Nikolai Smolyanskiy. 2026-10-08. LeWAM: A JEPA World Action Model with Diffusion-Steering-Based MPC. https://arxiv.org/abs/2610.12407

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