# MolmoAct2 Policy

MolmoAct2 is the LeRobot policy implementation of
[MolmoAct2](https://allenai.org/blog/molmoact2), ported into the LeRobot
training, evaluation, checkpointing, and dataset interfaces for easier use with
LeRobot datasets.

This implementation currently supports training and evaluation for the regular
MolmoAct2 model. MolmoAct2-Think, which supports adaptive depth reasoning, is
not included in this LeRobot policy yet.

For the original MolmoAct2 training code used for the experiments reported in
the paper, see [allenai/molmoact2](https://github.com/allenai/molmoact2).

## Installation Requirements

Install LeRobot with the MolmoAct2 optional dependencies:

```bash
uv sync --locked --extra molmoact2
```

To run the models in this repository, you need an NVIDIA GPU. The current
mixed-precision path stores the complete action expert in fp32 and the large VLM
matrices in bf16. `policy.compile_model=true` optionally compiles the action
expert blocks while leaving the VLM, vision tower, connector, and policy wrapper
eager. This boundary passed same-start output, gradient, and optimizer-update
parity checks; compiling the bf16 VLM path did not.

Multi-GPU training through `accelerate` increases throughput and global batch
size. This path has been exercised on two-node, eight-GPU GB200 runs, but this
LeRobot port does not expose the original MolmoAct2 `fsdp_devices`
model-parallel training path. A one-GPU GB200 replay with two real prompt widths
produced one compiled action graph with no graph breaks, the same 55.15 GiB peak
memory as eager execution, and a modest steady-state speedup. Treat these as
implementation checks rather than portable throughput or ETA claims.

The repo has been tested with Ubuntu 22.04.

## Usage

To use MolmoAct2 in a LeRobot training config, set:

```bash
--policy.type=molmoact2
```

## Training

MolmoAct2 can be fine-tuned from either the released MolmoAct2 Hugging Face
checkpoint format or from a checkpoint already saved by LeRobot. Both routes use
the same LeRobot training loop, dataset transforms, checkpoint saving, and
logging. The difference is only how the initial policy weights and processor
state are loaded.

LeRobot disables dataset image augmentation by default. Keep
`--dataset.image_transforms.enable=true` in MolmoAct2 training commands. The
original MolmoAct2 transform recipe is not LeRobot's generic transform default,
so the first command also pins its 95% crop, 5-degree rotation, and color
jitter explicitly. The original recipe additionally applies a Gaussian blur
with probability 0.2; LeRobot's generic `RandomSubsetApply` configuration cannot
express that optional fourth transform without sometimes dropping one of the
three required transforms.

### Training With Original MolmoAct2 Weight

Use `policy.checkpoint_path` when starting from a released MolmoAct2 checkpoint,
for example `allenai/MolmoAct2` or `allenai/MolmoAct2-LIBERO`. LeRobot will load
the original HF model files, then build its own policy processor from the
dataset metadata and the policy options below.

The command below shows full fine-tuning on the merged LIBERO dataset from the
released base checkpoint. It uses bf16 model loading, 8 flow timesteps, the
official LIBERO quantile statistics, image augmentation, and LeRobot's
checkpointing/logging path. Do not substitute `lerobot/libero`'s approximate
metadata quantiles for the released `norm_stats.json`; their q01/q99 values are
not identical.

```bash
accelerate launch \
  --num_processes=8 \
  --mixed_precision=bf16 \
  -m lerobot.scripts.lerobot_train \
  --dataset.repo_id=lerobot/libero \
  --dataset.root=/path/to/lerobot/libero \
  --dataset.video_backend=pyav \
  --dataset.image_transforms.enable=true \
  --dataset.image_transforms.max_num_transforms=3 \
  --dataset.image_transforms.random_order=false \
  --dataset.image_transforms.tfs='{"crop":{"weight":1.0,"type":"RandomResizedCrop","kwargs":{"size":[256,256],"scale":[0.9025,0.9025],"ratio":[1.0,1.0]}},"rotation":{"weight":1.0,"type":"RandomRotation","kwargs":{"degrees":[-5.0,5.0],"interpolation":2}},"color":{"weight":1.0,"type":"ColorJitter","kwargs":{"brightness":0.2,"contrast":[0.8,1.2],"saturation":[0.8,1.2],"hue":0.05}}}' \
  --policy.type=molmoact2 \
  --policy.checkpoint_path=allenai/MolmoAct2 \
  --policy.device=cuda \
  --policy.action_mode=continuous \
  --policy.norm_tag=libero \
  --policy.norm_stats_path=/path/to/MolmoAct2-LIBERO/norm_stats.json \
  --policy.train_mode_vlm=fft \
  --policy.chunk_size=10 \
  --policy.n_action_steps=10 \
  --policy.setup_type="single franka robotic arm in libero" \
  --policy.control_mode="delta end-effector pose" \
  --policy.image_keys='["observation.images.image","observation.images.image2"]' \
  --policy.dtype=bfloat16 \
  --policy.num_flow_timesteps=8 \
  --policy.gradient_checkpointing=true \
  --policy.compile_model=true \
  --policy.freeze_embedding=true \
  --policy.normalize_gripper=false \
  --policy.enable_knowledge_insulation=false \
  --policy.push_to_hub=false \
  --wandb.enable=true \
  --wandb.entity=<wandb_entity> \
  --wandb.project=<wandb_project> \
  --job_name=<job_name> \
  --output_dir=outputs/<job_name> \
  --steps=10000 \
  --batch_size=32 \
  --num_workers=4 \
  --log_freq=20 \
  --env_eval_freq=-1 \
  --save_checkpoint=true \
  --save_freq=2000
```

### Training With LeRobot MolmoAct2 Weight

Use `policy.path` when starting from a MolmoAct2 checkpoint that was saved by
LeRobot, either from a local `pretrained_model` directory or from the Hub. This
restores the saved LeRobot policy config, model weights, processor, and
normalization statistics. You can still override training-time options such as
`batch_size`, `steps`, or `policy.action_mode`. Checkpoint loading is strict and
preserves the saved FFT or LoRA topology, so do not override
`policy.train_mode_vlm` when using `policy.path`. To start a new LoRA run,
initialize from HF weights with `policy.checkpoint_path` instead, for example
with `--policy.type=molmoact2`,
`--policy.checkpoint_path=allenai/MolmoAct2`, and
`--policy.train_mode_vlm=lora`.

```bash
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=/path/to/pretrained_model \
  --policy.device=cuda \
  --policy.action_mode=continuous \
  --policy.chunk_size=10 \
  --policy.n_action_steps=10 \
  --policy.dtype=bfloat16 \
  --policy.num_flow_timesteps=8 \
  --policy.gradient_checkpointing=true \
  --policy.compile_model=true \
  --wandb.enable=true \
  --wandb.entity=<wandb_entity> \
  --wandb.project=<wandb_project> \
  --job_name=<job_name> \
  --output_dir=outputs/<job_name> \
  --steps=10000 \
  --batch_size=32 \
  --num_workers=4 \
  --log_freq=20 \
  --env_eval_freq=-1 \
  --save_checkpoint=true \
  --save_freq=2000
```

### Common Practices

For fine-tuning on a comparatively small dataset, such as a single LIBERO suite
or a real-world dataset with less than 200 demonstrations, a global batch size of
16 to 32 is a good starting point. In these settings, we recommend using
`policy.train_mode_vlm=lora` (the default), which usually gives similar or even
better performance than `fft`. Additionally, `policy.train_mode_vlm=freeze` is
also a practical choice. In all modes, we intentionally keep the action expert
fully trainable, which we found to be crucial for model performance. For larger
fine-tuning datasets, larger global batch sizes and full VLM fine-tuning
(`policy.train_mode_vlm=fft`) are usually preferred.

### Common Policy Options

- `policy.checkpoint_path`: original MolmoAct2 HF checkpoint to initialize from.
  Use this for released MolmoAct2 weights.
- `policy.path`: LeRobot checkpoint to initialize from. Use this for checkpoints
  created by LeRobot training.
- `policy.action_mode`: training target, one of `continuous`, `discrete`, or
  `both`. Official MolmoAct2 robot fine-tuning uses `continuous`. Released
  checkpoints retain discrete-action weights; `both` is available as an
  explicit joint flow-matching plus action-token ablation.
- `policy.train_mode_vlm`: controls the VLM fine-tuning mode, one of `fft`,
  `lora`, or `freeze`. `fft` fully fine-tunes the VLM, `lora` trains LoRA
  adapters on VLM linear layers, and `freeze` freezes the VLM. The action expert
  is fully fine-tuned in all three modes. The default is `lora`. `freeze`
  requires `policy.action_mode=continuous`.
- `policy.enable_knowledge_insulation`: when `true`, detaches action-expert
  context K/V states before the action loss. The default is `false`.
- `policy.chunk_size`: action horizon used by the policy. For LIBERO we use
  `10`. This LeRobot port overrides the loaded checkpoint's
  `max_action_horizon` with this value.
- `policy.n_action_steps`: number of actions consumed from each predicted
  chunk before querying the policy again. For LIBERO, set it to `chunk_size`.
- `policy.setup_type`: text inserted into the prompt to describe the robot and
  scene, e.g. `single franka robotic arm in libero`. More examples are listed
  in the `metadata_by_tag` entries of
  [`norm_stats.json`](https://huggingface.co/allenai/MolmoAct2/blob/main/norm_stats.json).
- `policy.control_mode`: text inserted into the prompt to describe the action
  space, e.g. `delta end-effector pose` or `absolute joint pose`.
- `policy.image_keys`: ordered LeRobot image observation keys passed to the
  processor.
- `policy.dtype`: Pi0.5-style precision switch. `bfloat16` uses bf16
  autocast/storage for large VLM matrices while retaining the complete action
  expert and numerically sensitive modules in fp32. `float32` disables
  autocast and keeps the full model in fp32. The low-memory `bfloat16` profile
  intentionally differs from the original MolmoAct2 FP32-master AMP run:
  AdamW moments follow each parameter's storage dtype, so the large bf16 VLM
  parameters also have bf16 moments. Full fine-tuning lazily allocates one bf16
  compensation tensor for each gradient-bearing bf16 parameter so updates
  smaller than one parameter ULP are carried into later steps. This is not an
  fp32 master copy. LoRA adapters, the action expert, and explicitly sensitive
  modules retain fp32 parameters and optimizer state; frozen VLM parameters in
  LoRA mode allocate no compensation tensor.
- `policy.compile_model`: enables MolmoAct2's block-wise `torch.compile` path.
  Full fine-tuning and LoRA both compile only the action-expert transformer
  blocks. Eager VLM/ViT/connector execution avoids compiler-induced BF16
  activation and gradient drift while retaining acceleration for the action
  path evaluated at every flow timestep. Inductor is also instructed to
  preserve eager BF16 downcast/upcast boundaries across fused operations. This
  is one fixed precision-safe boundary and does not add another compile option.
  Compilation is disabled by default; enable it for long GPU training runs.
  The action blocks use PyTorch's automatic shape strategy. With gradient
  checkpointing, only the variable encoder-context sequence dimension is marked
  dynamic; batch size, action horizon, and flow-timestep count remain static.
  Dynamo graph-cache reordering and its extra DDP graph splitter are disabled in
  that mode so backward recomputation selects the same block graph as forward.
  Batch-local text/action sequences are left-padded to an internal multiple of
  8 before BOS insertion. This adds at most seven masked tokens while sharply
  reducing shape-specific compile warm-up; it is not a user-facing option.
- `policy.num_flow_timesteps`: number of flow-matching timesteps sampled per
  example during training. We use `8` for fine-tuning.
- `policy.num_inference_steps`: optional override for continuous action
  generation steps at inference time.
- `policy.gradient_checkpointing`: enables checkpointing in the VLM/action path
  to reduce activation memory.
- `policy.freeze_embedding`: freezes input embeddings. The default is `true`.
- `policy.normalize_gripper`: controls whether gripper dimensions are included
  in state/action quantile normalization. The default is `false`.
- `policy.normalize_language`: normalizes task strings before prompt
  construction. The default is `true`.
- `policy.mask_action_dim_padding`: masks padded dimensions in the flow loss.
  Released checkpoints use `policy.expected_max_action_dim=32`.
- `policy.max_sequence_length`: optional manual sequence cap. Leave unset to
  infer it from images, state dimension, action dimension, action horizon, and
  discrete-action mode.

### Learning Rates

MolmoAct2 uses parameter-group learning rates to match the original MolmoAct2
fine-tuning experiments.

- Full fine-tuning uses `policy.optimizer_lr=1e-5` for the VLM,
  `policy.optimizer_vit_lr=5e-6` for the vision tower,
  `policy.optimizer_connector_lr=5e-6` for image connector layers, and
  `policy.optimizer_action_expert_lr=5e-5` for the action expert.
- LoRA VLM fine-tuning sets the VLM, vision, and connector LoRA parameter
  groups to `5e-5` when `policy.train_mode_vlm=lora`; the action expert is still
  fully fine-tuned with `policy.optimizer_action_expert_lr`.
- Frozen-VLM fine-tuning uses `policy.train_mode_vlm=freeze`, trains only the
  action expert, and uses `policy.optimizer_action_expert_lr=5e-5`.
- `policy.optimizer_grad_clip_norm` is applied independently to the LLM, vision
  tower, image connector, and action-expert parameter groups, matching the
  original MolmoAct2 optimizer. It is not a single global-model gradient norm.

You can override the full fine-tuning and action-expert learning rates with
`policy.optimizer_lr`, `policy.optimizer_vit_lr`,
`policy.optimizer_connector_lr`, and `policy.optimizer_action_expert_lr`.
Scheduler settings can be changed with `policy.scheduler_warmup_steps`,
`policy.scheduler_decay_steps`, and `policy.scheduler_decay_lr`. The default
24,000-step decay horizon matches the official
[`train_lerobot.py`](https://github.com/allenai/molmoact2/blob/5aac8f8a1180d79757ce500f819a02217079811c/experiments/launch_scripts/train_lerobot.py#L867-L868)
recipe.

### Dataset Quantile Statistics

MolmoAct2 defaults to quantile normalization for state and action features. If
your dataset has not been converted with quantile statistics, you can add them
with:

```bash
python src/lerobot/scripts/augment_dataset_quantile_stats.py \
  --repo-id=your_dataset
```

Recording, resuming, and merging aggregate quantiles from per-episode summaries, so `meta/stats.json` ends up holding a conservative envelope (`min` for `q <= 50`, `max` for `q > 50`) rather than whole-dataset quantiles. To estimate the latter, scan every episode with a running histogram:

```bash
python src/lerobot/scripts/augment_dataset_quantile_stats.py \
  --repo-id=your_dataset \
  --overwrite \
  --skip-images
```

`--skip-images` keeps the existing image statistics and avoids video decoding when only `STATE`/`ACTION` need recomputing, and `--root` reads a local dataset instead of the Hub. These values are histogram estimates, subject to discretization and rebinning error, so they can differ from the conservative ones — which changes MolmoAct2's normalized targets and therefore its loss scale. Statistics already saved inside an existing checkpoint are not affected.

Alternatively, train MolmoAct2 with mean/std normalization:

```bash
--policy.normalization_mapping='{"ACTION": "MEAN_STD", "STATE": "MEAN_STD", "VISUAL": "IDENTITY"}'
```

## Evaluation

Evaluation also supports both LeRobot-saved checkpoints and original MolmoAct2
HF checkpoints. For LIBERO replication, keep the EGL rendering environment
fixed and use `policy.per_episode_seed=true`.

**Important:** We found that `num_steps_wait=10` does not reliably let the
LIBERO scene stabilize and can degrade measured success. All LIBERO evaluation
results reported here use `num_steps_wait=50`.

### Evaluation With LeRobot MolmoAct2 Weight

Use `policy.path` for a checkpoint saved by LeRobot. The saved processor and
normalization statistics are restored together with the model.

```bash
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.dtype=bfloat16 \
  --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
```

### Evaluation With Original MolmoAct2 Weight

You can evaluate a released Hugging Face checkpoint directly without first
converting it to a LeRobot checkpoint. In this case, set
`policy.checkpoint_path` to the HF model repo and provide `policy.norm_tag`.
For LIBERO, `policy.norm_tag=libero` loads the LIBERO action/state
normalization statistics, action horizon, prompt metadata, and image-key order
from the checkpoint's `norm_stats.json`.

To fully replicate the MolmoAct2 paper results with released Hugging Face
checkpoints, we recommend using the v0.5.1-pinned
[`allenai/lerobot` `molmoact2-hf-inference`](https://github.com/allenai/lerobot/tree/molmoact2-hf-inference)
branch. That branch matches the original evaluation settings used for the
reported numbers.

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

lerobot-eval \
  --policy.type=molmoact2 \
  --policy.checkpoint_path=allenai/MolmoAct2-LIBERO \
  --policy.norm_tag=libero \
  --policy.inference_action_mode=continuous \
  --policy.dtype=float32 \
  --policy.enable_inference_cuda_graph=true \
  --policy.device=cuda \
  --policy.per_episode_seed=true \
  --policy.eval_seed=1000 \
  --env.type=libero \
  --env.task=libero_goal \
  --env.camera_name_mapping='{"agentview_image":"image","robot0_eye_in_hand_image":"wrist_image"}' \
  --eval.batch_size=1 \
  --eval.n_episodes=50 \
  --seed=1000
```

Use `--env.task=libero_10,libero_goal,libero_object,libero_spatial` to run the
full LIBERO suite. The same command works for other released MolmoAct2
checkpoints as long as the requested `policy.norm_tag` exists in that
checkpoint's `norm_stats.json`.

### Common Evaluation Options

- `policy.inference_action_mode`: required for rollout. Use `continuous` for
  flow-matching inference or `discrete` for action-token inference. It must be
  compatible with the training-time `policy.action_mode` saved in the
  checkpoint.
- `policy.path`: LeRobot checkpoint path or Hub repo. Use this for checkpoints
  saved by LeRobot.
- `policy.checkpoint_path`: original MolmoAct2 HF checkpoint path or Hub repo.
  Use this with `policy.type=molmoact2` and `policy.norm_tag`.
- `policy.norm_tag`: selects normalization statistics, prompt metadata,
  image-key order, and action horizon from the original checkpoint's
  `norm_stats.json`. It is required for direct original-HF checkpoint
  evaluation.
- `policy.dtype`: model storage/autocast profile. Use `bfloat16` for normal GPU
  evaluation. Use `float32` only when you explicitly want full-fp32 inference.
- `policy.enable_inference_cuda_graph`: enables the MolmoAct2 inference CUDA
  graph path for faster repeated continuous-action rollout.
- `policy.per_episode_seed` and `policy.eval_seed`: make stochastic continuous
  action generation deterministic per episode for replication.
- `env.task`: comma-separated LIBERO suites or a single suite. Use
  `libero_10,libero_goal,libero_object,libero_spatial` for the full benchmark.
- `env.camera_name_mapping`: maps LIBERO camera names to the image keys expected
  by the policy processor.

## Performance Results

### LIBERO Benchmark Results

MolmoAct2 has demonstrated strong performance on the LIBERO benchmark suite. To
compare and test its LeRobot implementation, we fine-tuned
[`allenai/MolmoAct2-LIBERO`](https://huggingface.co/allenai/MolmoAct2-LIBERO)
for an additional 10k steps on the LIBERO dataset with per-GPU batch size 32 on
8 H100 GPUs, then compared the results to the original MolmoAct2 reference
results.

The LeRobot fine-tuned checkpoint reported here is available at
[`allenai/MolmoAct2-LIBERO-LeRobot`](https://huggingface.co/allenai/MolmoAct2-LIBERO-LeRobot)
and was trained on
[`allenai/MolmoAct2-LIBERO-Dataset`](https://huggingface.co/datasets/allenai/MolmoAct2-LIBERO-Dataset).

| Benchmark      | LeRobot Implementation | MolmoAct2 Original |
| -------------- | ---------------------: | -----------------: |
| LIBERO Spatial |                  98.4% |              97.8% |
| LIBERO Object  |                 100.0% |             100.0% |
| LIBERO Goal    |                  98.0% |              97.8% |
| LIBERO 10      |                  96.6% |              93.2% |
| Average        |                 98.25% |             97.20% |

These results demonstrate MolmoAct2's strong performance across diverse robotic
manipulation tasks. To reproduce them, follow the instructions in the LIBERO
evaluation section.

## Hardware Deployment (lerobot-rollout)

LeRobot-format checkpoints are available on the Hub for direct use with
`lerobot-rollout`. Each checkpoint uses specific camera names that must
match your robot's camera configuration.

### Camera naming convention

Each checkpoint expects specific `observation.images.*` keys.
If your robot cameras have different names, use `--rename_map` to map them:

| Checkpoint                    | Camera keys            | Description              |
| ----------------------------- | ---------------------- | ------------------------ |
| MolmoAct2-LIBERO-LeRobot      | `image`, `wrist_image` | LIBERO sim cameras       |
| MolmoAct2-BimanualYAM-LeRobot | `top`, `left`, `right` | YAM 3-camera setup       |
| MolmoAct2-DROID-LeRobot       | `cam0`, `cam1`         | External + wrist         |
| MolmoAct2-SO100_101-LeRobot   | `cam0`, `cam1`         | Primary + secondary view |

Example with an SO-100 robot using top and side cameras:

```bash
lerobot-rollout \
  --policy.path=lerobot/MolmoAct2-SO100_101-LeRobot \
  --rename_map='{"observation.images.top": "observation.images.cam0", "observation.images.side": "observation.images.cam1"}' \
  --robot.type=so100_follower \
  --robot.port=/dev/ttyACM0 \
  --robot.cameras='{
      top: {type: opencv, index_or_path: 0, width: 640, height: 480, fps: 30},
      side: {type: opencv, index_or_path: 2, width: 640, height: 480, fps: 30}
  }' \
  --task="pick up the red cube" --duration=30
```

To use a wrist camera instead, just change the rename mapping:

```bash
--rename_map='{"observation.images.top": "observation.images.cam0", "observation.images.wrist": "observation.images.cam1"}'
```

### Joint frame transform (SO-100/101 zero-shot)

The MolmoAct2-SO100_101 checkpoint was trained on data that uses a different
joint calibration convention than LeRobot >= 0.5.0. Without a frame
correction, the arm may move in the wrong direction.

This affects both **zero-shot deployment** and **fine-tuning** from the
original checkpoint. The pretrained weights expect the old convention, so
all joint data (observations and actions) must be transformed to match.

The converted LeRobot checkpoint (`lerobot/MolmoAct2-SO100_101-LeRobot`)
already includes this correction in its processor pipeline. If you convert
or fine-tune the checkpoint yourself, set the following in the policy config (`configuration_molmoact2.py`):

- `joint_signs`: `[1, -1, 1, 1, 1, 1]` (flips shoulder_lift direction)
- `joint_offsets`: `[0, 90, 90, 0, 0, 0]` (shifts shoulder_lift and elbow_flex by 90°)

See the [backward compatibility guide](./backwardcomp) for details on the
calibration change.

## Differences From the Original Implementation

This LeRobot port is intended to match MolmoAct2 behavior while using LeRobot's
dataset, training, evaluation, checkpoint, and logging infrastructure. The main
differences from the original training repository are:

- The original paper training stack keeps fp32 master parameters and trains
  under bf16 AMP. This LeRobot port uses `policy.dtype=bfloat16` to lower
  memory: large VLM matrices are stored in bf16, while the action expert and
  numerically sensitive modules remain in fp32 and eligible operators run
  under bf16 autocast. A bf16 update-compensation tensor reduces parameter
  rounding loss during full fine-tuning, but its bf16 Adam moments still do not
  exactly reproduce the original fp32 optimizer state.
- The original repository uses its own FSDP/model-parallel training path. The
  LeRobot port uses the standard LeRobot/Accelerate training path and has not
  been tested for multi-node training.
- The original repository supports sequence packing. The LeRobot port trains on
  one LeRobot sample per item and uses batch-local padding with an inferred
  maximum sequence-length guard.
- The LeRobot port follows LeRobot's optimizer, scheduler, checkpoint saving,
  dataset transforms, image augmentation, and Weights & Biases logging
  conventions.
- The original training path supports mixed action horizons by padding to
  `max_action_horizon` and masking padded horizon slots in the action expert
  self-attention. This is useful when training across datasets with different
  control frequencies. The LeRobot port currently targets single-dataset
  fine-tuning, so `policy.chunk_size` overrides the checkpoint
  `max_action_horizon` and horizon masking is not implemented yet. Support for
  this mixed-horizon path is planned.

## Citation

```bibtex
@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),
consistent with [allenai/molmoact2](https://github.com/allenai/molmoact2).

