MolmoAct2-LIBERO (LeRobot)

This MolmoAct2 checkpoint is the LeRobot version of MolmoAct2-LIBERO, fine-tuned and evaluated on LIBERO tasks.

This checkpoint was fine-tuned from allenai/MolmoAct2-LIBERO for an additional 10k steps on allenai/MolmoAct2-LIBERO-Dataset with per-GPU batch size 32 on 8 H100 GPUs.

Original paper: MolmoAct2: Action Reasoning Models for Real-world Deployment
Reference implementation: https://github.com/allenai/molmoact2
LeRobot policy: lerobot.policies.molmoact2

Model Description

• Inputs: multi-view RGB images, robot state, and language instruction
• Outputs: continuous robot actions for LIBERO
• Training objective: flow matching and discrete action-token losses
• Action representation: continuous inference from the flow-matching action expert
• Base checkpoint: allenai/MolmoAct2-LIBERO
• Fine-tuning dataset: allenai/MolmoAct2-LIBERO-Dataset
• Intended use: LeRobot checkpoint for LIBERO evaluation and as a starting point for fine-tuning MolmoAct2 on related robot datasets

This LeRobot checkpoint restores the policy config, model weights, preprocessor, postprocessor, and normalization statistics through policy.path.

Results

These results use continuous action inference with per-episode seeding.

Quick Start

Installation

Install a LeRobot version that includes the MolmoAct2 policy:

pip install "lerobot[molmoact2,libero] @ git+https://github.com/huggingface/lerobot.git"

For full LeRobot installation details, see the official documentation: https://huggingface.co/docs/lerobot/installation

Load Model and Run select_action

import torch
from lerobot.datasets.lerobot_dataset import LeRobotDataset
from lerobot.policies.factory import make_pre_post_processors
from lerobot.policies.molmoact2 import MolmoAct2Policy

model_id = "allenai/MolmoAct2-LIBERO-LeRobot"
dataset_id = "allenai/MolmoAct2-LIBERO-Dataset"
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")

policy = MolmoAct2Policy.from_pretrained(model_id).to(device).eval()

preprocess, postprocess = make_pre_post_processors(
    policy.config,
    model_id,
    preprocessor_overrides={"device_processor": {"device": str(device)}},
)

dataset = LeRobotDataset(dataset_id)
frame = dict(dataset[0])

batch = preprocess(frame)
with torch.inference_mode():
    action = policy.select_action(batch, inference_action_mode="continuous")
    action = postprocess(action)

Training Step

For fine-tuning, MolmoAct2 follows the standard LeRobot policy API. A training batch should include the observation keys, state, task text, and action chunk prepared by the LeRobot dataloader and MolmoAct2 preprocessor.

policy.train()
batch = preprocess(dict(dataset[0]))

loss, metrics = policy.forward(batch)
loss.backward()

Use lerobot-train for full training loops, checkpointing, logging, and distributed execution.

Fine-Tuning

To continue fine-tuning this LeRobot checkpoint on LIBERO:

accelerate launch \
  --num_processes=8 \
  --mixed_precision=bf16 \
  -m lerobot.scripts.lerobot_train \
  --dataset.repo_id=allenai/MolmoAct2-LIBERO-Dataset \
  --dataset.root=/path/to/lerobot/data/allenai/MolmoAct2-LIBERO-Dataset \
  --dataset.video_backend=pyav \
  --dataset.image_transforms.enable=true \
  --policy.path=allenai/MolmoAct2-LIBERO-LeRobot \
  --policy.device=cuda \
  --policy.action_mode=both \
  --policy.chunk_size=10 \
  --policy.n_action_steps=10 \
  --policy.model_dtype=bfloat16 \
  --policy.num_flow_timesteps=8 \
  --policy.gradient_checkpointing=true \
  --wandb.enable=false \
  --job_name=<job_name> \
  --output_dir=outputs/<job_name> \
  --steps=10000 \
  --batch_size=32 \
  --num_workers=4 \
  --log_freq=20 \
  --eval_freq=-1 \
  --save_checkpoint=true \
  --save_freq=2000

Common MolmoAct2 options:

• policy.action_mode=both trains continuous flow matching and discrete action tokens.
• policy.inference_action_mode=continuous selects the continuous action head for rollout.
• policy.chunk_size=10 is the LIBERO action horizon used by this checkpoint.
• policy.n_action_steps=10 consumes the full predicted LIBERO action chunk.
• policy.model_dtype=bfloat16 is recommended for GPU training.
• policy.num_flow_timesteps=8 matches the MolmoAct2 fine-tuning setup.
• policy.gradient_checkpointing=true reduces activation memory.

When using policy.path, the saved LeRobot processor is restored from this checkpoint. That means LIBERO-specific prompt and input settings such as setup_type, control_mode, image_keys, and normalization statistics are loaded from the checkpoint rather than supplied in the command above. This is the recommended path for continuing LIBERO fine-tuning.

Set --wandb.enable=true and provide --wandb.entity and --wandb.project if you want to log the run to Weights & Biases.

For a different robot setup, control space, or camera layout, initialize from an original MolmoAct2 checkpoint with policy.checkpoint_path and explicitly set the corresponding policy fields while creating a new LeRobot checkpoint.

Evaluate in Simulation

You can evaluate this checkpoint in LIBERO with lerobot-eval:

export MUJOCO_GL=egl
export PYOPENGL_PLATFORM=egl
export OMP_NUM_THREADS=1
export MKL_NUM_THREADS=1

lerobot-eval \
  --policy.path=allenai/MolmoAct2-LIBERO-LeRobot \
  --policy.inference_action_mode=continuous \
  --policy.model_dtype=bfloat16 \
  --policy.use_amp=true \
  --policy.enable_inference_cuda_graph=true \
  --policy.device=cuda \
  --policy.per_episode_seed=true \
  --policy.eval_seed=1000 \
  --env.type=libero \
  --env.task=libero_10,libero_goal,libero_object,libero_spatial \
  --env.camera_name_mapping='{"agentview_image":"image","robot0_eye_in_hand_image":"wrist_image"}' \
  --eval.batch_size=1 \
  --eval.n_episodes=50 \
  --seed=1000

Notes

• This checkpoint is saved in LeRobot format. Use policy.path, not policy.checkpoint_path, when you want to evaluate it or continue LIBERO fine-tuning with the saved processor.
• The reported LIBERO numbers use continuous inference.
• The checkpoint was trained with policy.action_mode=both, so discrete action inference is also supported by the model, but the reported LIBERO results use policy.inference_action_mode=continuous.
• Released MolmoAct2 checkpoints have a fixed maximum action dimension of 32. Padded dimensions are masked in the flow loss.

Citation

@misc{fang2026molmoact2actionreasoningmodels,
      title={MolmoAct2: Action Reasoning Models for Real-world Deployment},
      author={Haoquan Fang and Jiafei Duan and Donovan Clay and Sam Wang and Shuo Liu and Weikai Huang and Xiang Fan and Wei-Chuan Tsai and Shirui Chen and Yi Ru Wang and Shanli Xing and Jaemin Cho and Jae Sung Park and Ainaz Eftekhar and Peter Sushko and Karen Farley and Angad Wadhwa and Cole Harrison and Winson Han and Ying-Chun Lee and Eli VanderBilt and Rose Hendrix and Suveen Ellawela and Lucas Ngoo and Joyce Chai and Zhongzheng Ren and Ali Farhadi and Dieter Fox and Ranjay Krishna},
      year={2026},
      eprint={2605.02881},
      archivePrefix={arXiv},
      primaryClass={cs.RO},
      url={https://arxiv.org/abs/2605.02881},
}

License

This model is licensed under Apache 2.0. It is intended for research and educational use in accordance with Ai2's Responsible Use Guidelines: https://allenai.org/responsible-use