Training Vision-Language-Action Models with Dense Embodied Chain-of-Thought Supervision

Haoyang Li; Guanlin Li; Youhe Feng; Chen Zhao; Zhuoran Wang; Yang Li; Qizhe Wei; Shifeng Bao; Haitao Shen; Yihan Zhao; Tong Yang; Jing Zhang

arXiv · 2606.30552

Training Vision-Language-Action Models with Dense Embodied Chain-of-Thought Supervision

Haoyang Li·Guanlin Li·Youhe Feng·Chen Zhao·Zhuoran Wang·Yang Li·Qizhe Wei·Shifeng Bao·Haitao Shen·Yihan Zhao·Tong Yang·Jing Zhang

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Abstract

Cross-embodiment transfer in vision-language-action (VLA) models remains challenging because low-level state and action spaces differ fundamentally across robot platforms. We observe that the high-level cognitive process underlying manipulation, including scene perception, object identification, task planning, and sub-task decomposition, is largely shared across embodiments. Based on this observation, we present ZR-0, a 2.6 billion parameter end-to-end VLA model that uses dense Embodied Chain-of-Thought (ECoT) supervision to align cross-embodiment representations within the vision-language model (VLM). ZR-0 adopts a dual-stream architecture: a pre-trained VLM (System 2) generates structured ECoT reasoning during training, while a Diffusion Transformer-based action expert (System 1) produces continuous action chunks via flow matching. The two components are coupled through cross-attention, with an attention mask that restricts the action expert to input prompt features only, enabling ECoT generation to be entirely skipped at inference without any performance loss. ZR-0 is pre-trained on ProcCorpus-60M, a large-scale dataset comprising approximately 60 million frames (approximately 1,000 hours) from over 400K trajectories, with dense ECoT annotations covering 96.8% of all frames. We evaluate ZR-0 on three simulation benchmarks spanning single-arm (LIBERO), bimanual (RoboTwin 2.0), and humanoid (RoboCasa GR-1 Tabletop) embodiments, as well as real-world experiments on the xArm platform, demonstrating strong performance across all settings. Code and model checkpoints are available at https://github.com/RUCKBReasoning/ZR-0.

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Haoyang Li, Guanlin Li, Youhe Feng, Chen Zhao, Zhuoran Wang, Yang Li, Qizhe Wei, Shifeng Bao, Haitao Shen, Yihan Zhao, Tong Yang, Jing Zhang. 2026-06-29. Training Vision-Language-Action Models with Dense Embodied Chain-of-Thought Supervision. https://arxiv.org/abs/2606.30552

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