Pepijn af6d8ebd5b feat(smolvla2): dual-head forward — flow loss + lm_head text loss
The third and final commit of PR 3's SmolVLA2 work. Wires the actual
training signal through:

* ``predict_actions[i] = True``  → sample i contributes to flow loss
* ``text_labels[i, t] != -100``  → token t of sample i contributes to
                                    LM-head cross-entropy

Both routing knobs come from ``SmolVLA2ChatTokenizerStep`` (previous
commit on this branch), which builds them from the recipe's
``message_streams`` / ``target_message_indices``. The per-sample
``predict_actions`` mask preserves the Pi0.5 convention from the
plan's Section I.7: "True iff any low_level target exists".

Implementation:

- ``forward`` reads ``text_labels`` and ``predict_actions`` from the
  batch. When neither is present (vanilla SmolVLA usage with no
  recipe), delegates to ``SmolVLAPolicy.forward`` so unannotated
  datasets keep training as before — full backward compatibility.
- ``flow_loss``: super().forward(reduction="none") returns the
  per-sample (B,) flow loss; we mask non-action samples with the
  ``predict_actions`` bool and renormalize by the count of action
  samples. ``flow_loss_weight = 0`` in the config disables this
  branch entirely (text-only training).
- ``text_loss``: a prefix-only forward through the VLM (no action
  expert / suffix), slicing the lang-token range out of the
  resulting hidden states (``embed_prefix`` orders the prefix as
  ``[image_blocks..., lang, state]`` so the slice is unambiguous).
  Apply ``vlm.lm_head`` to those hidden states, cross-entropy with
  ``text_labels`` (ignore_index=-100). ``text_loss_weight = 0``
  disables this branch (reverts to flow-only behaviour, matching
  SmolVLA exactly).
- The two losses are summed with the config-supplied weights.

Mixed-stream samples (one batch containing both action targets and
text-only sub-recipes) are handled correctly: each sample contributes
where its labels are valid and is masked elsewhere.

Limitations / known follow-ups:

- Text loss runs an additional prefix-only forward separate from the
  flow path's prefix forward. The forwards could share their prefix
  computation; for clarity of this first commit they don't.
  Optimization is straightforward when needed.
- Per-sample loss for ``reduction="none"`` is not yet meaningfully
  defined for the dual path — we broadcast the scalar to (B,) for
  caller compatibility (e.g. RA-BC weighting will need follow-up).
- Inference ``select_action`` is unchanged from SmolVLA today —
  it predicts actions only. A separate "generate text"
  ``select_message`` path is the natural next step for runtime
  use of the LM head (memory updates, plan refreshes, VQA answers).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-04-30 19:54:57 +02:00
2025-03-13 14:05:55 +01:00
2025-06-05 17:48:43 +02:00
2026-04-06 12:23:37 +02:00
2026-02-28 14:41:28 +01:00
2024-03-25 12:28:07 +01:00
2026-01-16 14:38:42 +01:00

LeRobot, Hugging Face Robotics Library

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LeRobot aims to provide models, datasets, and tools for real-world robotics in PyTorch. The goal is to lower the barrier to entry so that everyone can contribute to and benefit from shared datasets and pretrained models.

🤗 A hardware-agnostic, Python-native interface that standardizes control across diverse platforms, from low-cost arms (SO-100) to humanoids.

🤗 A standardized, scalable LeRobotDataset format (Parquet + MP4 or images) hosted on the Hugging Face Hub, enabling efficient storage, streaming and visualization of massive robotic datasets.

🤗 State-of-the-art policies that have been shown to transfer to the real-world ready for training and deployment.

🤗 Comprehensive support for the open-source ecosystem to democratize physical AI.

Quick Start

LeRobot can be installed directly from PyPI.

pip install lerobot
lerobot-info

Important

For detailed installation guide, please see the Installation Documentation.

Robots & Control

Reachy 2 Demo

LeRobot provides a unified Robot class interface that decouples control logic from hardware specifics. It supports a wide range of robots and teleoperation devices.

from lerobot.robots.myrobot import MyRobot

# Connect to a robot
robot = MyRobot(config=...)
robot.connect()

# Read observation and send action
obs = robot.get_observation()
action = model.select_action(obs)
robot.send_action(action)

Supported Hardware: SO100, LeKiwi, Koch, HopeJR, OMX, EarthRover, Reachy2, Gamepads, Keyboards, Phones, OpenARM, Unitree G1.

While these devices are natively integrated into the LeRobot codebase, the library is designed to be extensible. You can easily implement the Robot interface to utilize LeRobot's data collection, training, and visualization tools for your own custom robot.

For detailed hardware setup guides, see the Hardware Documentation.

LeRobot Dataset

To solve the data fragmentation problem in robotics, we utilize the LeRobotDataset format.

  • Structure: Synchronized MP4 videos (or images) for vision and Parquet files for state/action data.
  • HF Hub Integration: Explore thousands of robotics datasets on the Hugging Face Hub.
  • Tools: Seamlessly delete episodes, split by indices/fractions, add/remove features, and merge multiple datasets.
from lerobot.datasets.lerobot_dataset import LeRobotDataset

# Load a dataset from the Hub
dataset = LeRobotDataset("lerobot/aloha_mobile_cabinet")

# Access data (automatically handles video decoding)
episode_index=0
print(f"{dataset[episode_index]['action'].shape=}\n")

Learn more about it in the LeRobotDataset Documentation

SoTA Models

LeRobot implements state-of-the-art policies in pure PyTorch, covering Imitation Learning, Reinforcement Learning, and Vision-Language-Action (VLA) models, with more coming soon. It also provides you with the tools to instrument and inspect your training process.

Gr00t Architecture

Training a policy is as simple as running a script configuration:

lerobot-train \
  --policy=act \
  --dataset.repo_id=lerobot/aloha_mobile_cabinet
Category Models
Imitation Learning ACT, Diffusion, VQ-BeT, Multitask DiT Policy
Reinforcement Learning HIL-SERL, TDMPC & QC-FQL (coming soon)
VLAs Models Pi0Fast, Pi0.5, GR00T N1.5, SmolVLA, XVLA

Similarly to the hardware, you can easily implement your own policy & leverage LeRobot's data collection, training, and visualization tools, and share your model to the HF Hub

For detailed policy setup guides, see the Policy Documentation.

Inference & Evaluation

Evaluate your policies in simulation or on real hardware using the unified evaluation script. LeRobot supports standard benchmarks like LIBERO, MetaWorld and more to come.

# Evaluate a policy on the LIBERO benchmark
lerobot-eval \
  --policy.path=lerobot/pi0_libero_finetuned \
  --env.type=libero \
  --env.task=libero_object \
  --eval.n_episodes=10

Learn how to implement your own simulation environment or benchmark and distribute it from the HF Hub by following the EnvHub Documentation

Resources

Citation

If you use LeRobot in your project, please cite the GitHub repository to acknowledge the ongoing development and contributors:

@misc{cadene2024lerobot,
    author = {Cadene, Remi and Alibert, Simon and Soare, Alexander and Gallouedec, Quentin and Zouitine, Adil and Palma, Steven and Kooijmans, Pepijn and Aractingi, Michel and Shukor, Mustafa and Aubakirova, Dana and Russi, Martino and Capuano, Francesco and Pascal, Caroline and Choghari, Jade and Moss, Jess and Wolf, Thomas},
    title = {LeRobot: State-of-the-art Machine Learning for Real-World Robotics in Pytorch},
    howpublished = "\url{https://github.com/huggingface/lerobot}",
    year = {2024}
}

If you are referencing our research or the academic paper, please also cite our ICLR publication:

ICLR 2026 Paper
@inproceedings{cadenelerobot,
  title={LeRobot: An Open-Source Library for End-to-End Robot Learning},
  author={Cadene, Remi and Alibert, Simon and Capuano, Francesco and Aractingi, Michel and Zouitine, Adil and Kooijmans, Pepijn and Choghari, Jade and Russi, Martino and Pascal, Caroline and Palma, Steven and Shukor, Mustafa and Moss, Jess and Soare, Alexander and Aubakirova, Dana and Lhoest, Quentin and Gallou\'edec, Quentin and Wolf, Thomas},
  booktitle={The Fourteenth International Conference on Learning Representations},
  year={2026},
  url={https://arxiv.org/abs/2602.22818}
}

Contribute

We welcome contributions from everyone in the community! To get started, please read our CONTRIBUTING.md guide. Whether you're adding a new feature, improving documentation, or fixing a bug, your help and feedback are invaluable. We're incredibly excited about the future of open-source robotics and can't wait to work with you on what's next—thank you for your support!

SO101 Video

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