feat(train): FSDP checkpoint saving (#3810)

* feat(train): FSDP checkpoint saving

* adding docs for FSDP

* adding a test for the fsdp checkpoint path

* cleanup

* fixing final upload to hub

* refactored initial implementation to use torch fsdp api and adding new tests

README.md

@@ -136,6 +136,7 @@ Learn how to implement your own simulation environment or benchmark and distribu
 - **[X](https://x.com/LeRobotHF):** Follow us on X to stay up-to-date with the latest developments.
 - **[Robot Learning Tutorial](https://huggingface.co/spaces/lerobot/robot-learning-tutorial):** A free, hands-on course to learn robot learning using LeRobot.
 - **[T-Shirt Folding Experiment](https://huggingface.co/spaces/lerobot/robot-folding):** An end-to-end demonstration of folding t-shirts with LeRobot.
+- **[LeLab](https://github.com/huggingface/leLab):** A web interface for LeRobot — teleoperate, calibrate, record datasets, replay, and train your SO arm from the browser, no CLI required.
 
 ## Citation
 

docs/source/hil_data_collection.mdx

@@ -57,11 +57,11 @@ The `lerobot-rollout --strategy.type=dagger` mode requires **teleoperators with
 
 **Compatible teleoperators:**
 
-- `openarm_mini` - OpenArm Mini
+- `bi_openarm_mini` - Bimanual OpenArm Mini
 - `so_leader` - SO100 / SO101 leader arm
 
 > [!IMPORTANT]
-> The provided commands default to `bi_openarm_follower` + `openarm_mini`.
+> The provided commands default to `bi_openarm_follower` + `bi_openarm_mini`.
 > `so_follower` + `so_leader` configs are also registered and can be used via CLI flags.
 
 ---
@@ -104,9 +104,9 @@ lerobot-rollout --strategy.type=dagger \
     --robot.right_arm_config.port=can0 \
     --robot.right_arm_config.side=right \
     --robot.cameras='{left_wrist: {type: opencv, index_or_path: "/dev/video0", width: 1280, height: 720, fps: 30}, right_wrist: {type: opencv, index_or_path: "/dev/video4", width: 1280, height: 720, fps: 30}, base: {type: opencv, index_or_path: "/dev/video2", width: 640, height: 480, fps: 30}}' \
-    --teleop.type=openarm_mini \
+    --teleop.type=bi_openarm_mini \
-    --teleop.port_left=/dev/ttyACM0 \
+    --teleop.left_arm_config.port=/dev/ttyACM0 \
-    --teleop.port_right=/dev/ttyACM1 \
+    --teleop.right_arm_config.port=/dev/ttyACM1 \
     --policy.path=outputs/pretrain/checkpoints/last/pretrained_model \
     --dataset.repo_id=your-username/rollout_hil_dataset \
     --dataset.single_task="Fold the T-shirt properly" \
@@ -131,9 +131,9 @@ lerobot-rollout --strategy.type=dagger \
     --robot.right_arm_config.port=can0 \
     --robot.right_arm_config.side=right \
     --robot.cameras='{left_wrist: {type: opencv, index_or_path: "/dev/video0", width: 1280, height: 720, fps: 30}, right_wrist: {type: opencv, index_or_path: "/dev/video4", width: 1280, height: 720, fps: 30}, base: {type: opencv, index_or_path: "/dev/video2", width: 640, height: 480, fps: 30}}' \
-    --teleop.type=openarm_mini \
+    --teleop.type=bi_openarm_mini \
-    --teleop.port_left=/dev/ttyACM0 \
+    --teleop.left_arm_config.port=/dev/ttyACM0 \
-    --teleop.port_right=/dev/ttyACM1 \
+    --teleop.right_arm_config.port=/dev/ttyACM1 \
     --policy.path=outputs/pretrain/checkpoints/last/pretrained_model \
     --dataset.repo_id=your-username/rollout_hil_rtc_dataset \
     --dataset.single_task="Fold the T-shirt properly" \

docs/source/inference.mdx

@@ -117,7 +117,7 @@ lerobot-rollout \
     --strategy.num_episodes=20 \
     --policy.path=outputs/pretrain/checkpoints/last/pretrained_model \
     --robot.type=bi_openarm_follower \
-    --teleop.type=openarm_mini \
+    --teleop.type=bi_openarm_mini \
     --dataset.repo_id=${HF_USER}/rollout_hil_data \
     --dataset.single_task="Fold the T-shirt"
 ```

docs/source/multi_gpu_training.mdx

@@ -113,6 +113,61 @@ accelerate launch --num_processes=2 $(which lerobot-train) \
   --policy=act
 ```
 
+## Training Large Models with FSDP
+
+DDP replicates the full model on every GPU, so a model that doesn't fit on one GPU won't fit under
+DDP either. For large models, use **FSDP** (Fully Sharded Data Parallel), which shards parameters,
+gradients, and optimizer state across GPUs. See the [accelerate FSDP guide](https://huggingface.co/docs/accelerate/usage_guides/fsdp) for background.
+
+An example on how to launch LeRobot training with FSDP across 4 GPUs (1 machine):
+
+```bash
+accelerate launch --config_file fsdp.yaml --num_processes=4 $(which lerobot-train) \
+  --dataset.repo_id=${HF_USER}/my_dataset \
+  --policy.type=<your_policy> \
+  --output_dir=outputs/train/my_policy_fsdp
+```
+
+A minimal `fsdp.yaml` (FSDP1; shards params/grads/optimizer — ZeRO-3-equivalent):
+
+```yaml
+compute_environment: LOCAL_MACHINE
+distributed_type: FSDP
+mixed_precision: bf16
+num_machines: 1
+num_processes: 4
+fsdp_config:
+  fsdp_version: 1
+  fsdp_sharding_strategy: FULL_SHARD # params + grads + optimizer (ZeRO-3)
+  fsdp_auto_wrap_policy: TRANSFORMER_BASED_WRAP
+  fsdp_transformer_layer_cls_to_wrap: <YourTransformerBlock> # repeated block class to shard
+  fsdp_use_orig_params: true # required: optimizer is built pre-prepare
+  fsdp_state_dict_type: FULL_STATE_DICT
+```
+
+Set `fsdp_transformer_layer_cls_to_wrap` to your model's repeated transformer-block class so each
+block is sharded as its own unit. `fsdp_use_orig_params: true` is required because LeRobot builds the
+optimizer before `accelerator.prepare()`.
+
+### FSDP checkpoints
+
+LeRobot gathers the full state dict across all ranks and the main process writes it as a single
+`model.safetensors`, loadable as usual with `Policy.from_pretrained(...)`. Two things to look out for:
+
+- **Checkpoints store fp32 weights.** Under mixed precision (`bf16`/`fp16`) FSDP keeps an fp32 master
+  copy, and the checkpoint saves it (~2× the bf16 size on disk) so training can resume consistently
+  with the fp32 optimizer state; `from_pretrained` casts back to the policy dtype on load. FSDP-specific
+  caveat: an fp32 checkpoint is materialized in full precision on the target device _before_ casting,
+  so loading it for inference on a tight GPU can OOM even when the bf16 model would fit — load on CPU
+  first, or cast `model.safetensors` to the deployment dtype offline.
+- The sharded optimizer state is gathered into a full (world-size-independent) state dict and saved
+  alongside the model in the same `optimizer_state.safetensors` / `optimizer_param_groups.json`
+  format as single-GPU training, so **resume-from-checkpoint is supported** with `--resume=true`.
+  Resume reshards both the model and the optimizer state to the _current_ FSDP topology, so you can
+  resume an FSDP checkpoint on a different number of GPUs. Note that the data sampler is only
+  sample-exact when the world size and batch size match the original run (a warning is logged
+  otherwise); the optimizer/model state itself is unaffected.
+
 ## Notes
 
 - The `--policy.use_amp` flag in `lerobot-train` is only used when **not** running with accelerate. When using accelerate, mixed precision is controlled by accelerate's configuration.

src/lerobot/annotations/steerable_pipeline/writer.py

@@ -54,6 +54,7 @@ from typing import Any
 import pyarrow as pa
 import pyarrow.parquet as pq
 
+from lerobot.datasets.io_utils import write_table_one_row_group_per_episode
 from lerobot.datasets.language import (
     EVENT_ONLY_STYLES,
     LANGUAGE_EVENTS,
@@ -274,12 +275,11 @@ class LanguageColumnsWriter:
         new_table = self._materialize_table(
             table, per_row_persistent, per_row_events, drop_old=self.drop_existing_subtask_index
         )
-        # Atomic replace: write to a sibling tmp path and rename so a crash
+        # Re-emit one row group per episode (a bulk pq.write_table would collapse
-        # mid-write can't leave a half-written shard that ``pq.read_table``
+        # them into one). Write to a sibling tmp path and atomically rename so a
-        # would then fail to open. ``Path.replace`` is atomic on POSIX +
+        # crash mid-write can't leave a half-written shard.
-        # Windows when source and target sit on the same filesystem.
         tmp_path = path.with_suffix(path.suffix + ".tmp")
-        pq.write_table(new_table, tmp_path)
+        write_table_one_row_group_per_episode(new_table, tmp_path)
         tmp_path.replace(path)
 
     def _materialize_table(

src/lerobot/cameras/opencv/camera_opencv.py

@@ -442,11 +442,12 @@ class OpenCVCamera(Camera):
 
         Stops on DeviceNotConnectedError, logs other errors and continues.
         """
-        if self.stop_event is None:
+        stop_event = self.stop_event
+        if stop_event is None:
             raise RuntimeError(f"{self}: stop_event is not initialized before starting read loop.")
 
         failure_count = 0
-        while not self.stop_event.is_set():
+        while not stop_event.is_set():
             try:
                 raw_frame = self._read_from_hardware()
                 processed_frame = self._postprocess_image(raw_frame)

src/lerobot/cameras/realsense/camera_realsense.py

@@ -471,11 +471,12 @@ class RealSenseCamera(Camera):
 
         Stops on DeviceNotConnectedError, logs other errors and continues.
         """
-        if self.stop_event is None:
+        stop_event = self.stop_event
+        if stop_event is None:
             raise RuntimeError(f"{self}: stop_event is not initialized before starting read loop.")
 
         failure_count = 0
-        while not self.stop_event.is_set():
+        while not stop_event.is_set():
             try:
                 frame = self._read_from_hardware()
                 color_frame_raw = frame.get_color_frame()

src/lerobot/cameras/zmq/camera_zmq.py

@@ -246,11 +246,12 @@ class ZMQCamera(Camera):
         """
         Internal loop run by the background thread for asynchronous reading.
         """
-        if self.stop_event is None:
+        stop_event = self.stop_event
+        if stop_event is None:
             raise RuntimeError(f"{self}: stop_event is not initialized.")
 
         failure_count = 0
-        while not self.stop_event.is_set():
+        while not stop_event.is_set():
             try:
                 frame = self._read_from_hardware()
                 capture_time = time.perf_counter()

src/lerobot/common/train_utils.py

@@ -21,6 +21,7 @@ from torch.optim.lr_scheduler import LRScheduler
 from lerobot.configs.train import TrainPipelineConfig
 from lerobot.optim import (
     load_optimizer_state,
+    load_optimizer_state_dict,
     load_scheduler_state,
     save_optimizer_state,
     save_scheduler_state,
@@ -98,6 +99,8 @@ def save_checkpoint(
     postprocessor: PolicyProcessorPipeline | None = None,
     num_processes: int | None = None,
     batch_size: int | None = None,
+    model_state_dict: dict | None = None,
+    optim_state_dict: dict | None = None,
 ) -> None:
     """This function creates the following directory structure:
 
@@ -127,9 +130,18 @@ def save_checkpoint(
             resume. Defaults to None (not recorded).
         batch_size (int | None, optional): Per-process batch size to record for sample-exact
             resume. Defaults to None (not recorded).
+        model_state_dict: Pre-gathered full (unsharded) model state dict. Required under FSDP,
+            where `policy.state_dict()` would return sharded tensors; the caller gathers it via a
+            cross-rank collective and passes it here so rank 0 can write it directly. It holds
+            FSDP's fp32 master weights and is saved as-is (the loader casts to the policy dtype on
+            read). When None (DDP / single-GPU), the model is saved the normal way. Defaults to None.
+        optim_state_dict: Pre-gathered full (unsharded) optimizer state dict. Required under FSDP
+            (gathered alongside `model_state_dict` via `gather_fsdp_state_dicts`); saved in the same
+            safetensors format as the single-GPU path. When None, `optimizer.state_dict()` is used.
+            Defaults to None.
     """
     pretrained_dir = checkpoint_dir / PRETRAINED_MODEL_DIR
-    policy.save_pretrained(pretrained_dir)
+    policy.save_pretrained(pretrained_dir, state_dict=model_state_dict)
     cfg.save_pretrained(pretrained_dir)
     if cfg.peft is not None:
         # When using PEFT, policy.save_pretrained will only write the adapter weights + config, not the
@@ -140,7 +152,13 @@ def save_checkpoint(
     if postprocessor is not None:
         postprocessor.save_pretrained(pretrained_dir)
     save_training_state(
-        checkpoint_dir, step, optimizer, scheduler, num_processes=num_processes, batch_size=batch_size
+        checkpoint_dir,
+        step,
+        optimizer,
+        scheduler,
+        num_processes=num_processes,
+        batch_size=batch_size,
+        optim_state_dict=optim_state_dict,
     )
 
 
@@ -151,6 +169,7 @@ def save_training_state(
     scheduler: LRScheduler | None = None,
     num_processes: int | None = None,
     batch_size: int | None = None,
+    optim_state_dict: dict | None = None,
 ) -> None:
     """
     Saves the training step, optimizer state, scheduler state, and rng state.
@@ -164,19 +183,21 @@ def save_training_state(
             Defaults to None.
         num_processes (int | None, optional): Distributed world size to record. Defaults to None.
         batch_size (int | None, optional): Per-process batch size to record. Defaults to None.
+        optim_state_dict: Pre-gathered full optimizer state dict (for FSDP). Saved instead of
+            `optimizer.state_dict()` when provided. Defaults to None.
     """
     save_dir = checkpoint_dir / TRAINING_STATE_DIR
     save_dir.mkdir(parents=True, exist_ok=True)
     save_training_step(train_step, save_dir, num_processes=num_processes, batch_size=batch_size)
     save_rng_state(save_dir)
     if optimizer is not None:
-        save_optimizer_state(optimizer, save_dir)
+        save_optimizer_state(optimizer, save_dir, optim_state_dict=optim_state_dict)
     if scheduler is not None:
         save_scheduler_state(scheduler, save_dir)
 
 
 def load_training_state(
-    checkpoint_dir: Path, optimizer: Optimizer, scheduler: LRScheduler | None
+    checkpoint_dir: Path, optimizer: Optimizer, scheduler: LRScheduler | None, load_optimizer: bool = True
 ) -> tuple[int, Optimizer, LRScheduler | None]:
     """
     Loads the training step, optimizer state, scheduler state, and rng state.
@@ -186,6 +207,10 @@ def load_training_state(
         checkpoint_dir (Path): The checkpoint directory. Should contain a 'training_state' dir.
         optimizer (Optimizer): The optimizer to load the state_dict to.
         scheduler (LRScheduler | None): The scheduler to load the state_dict to (can be None).
+        load_optimizer (bool, optional): Whether to load the optimizer state from disk. Defaults to
+            True. Set to False under FSDP, where the sharded optimizer state must be loaded after
+            `accelerator.prepare()` via `load_fsdp_optimizer_state` (the optimizer is returned
+            untouched here).
 
     Raises:
         NotADirectoryError: If 'checkpoint_dir' doesn't contain a 'training_state' dir
@@ -200,8 +225,61 @@ def load_training_state(
 
     load_rng_state(training_state_dir)
     step = load_training_step(training_state_dir)
-    optimizer = load_optimizer_state(optimizer, training_state_dir)
+    if load_optimizer:
+        optimizer = load_optimizer_state(optimizer, training_state_dir)
     if scheduler is not None:
         scheduler = load_scheduler_state(scheduler, training_state_dir)
 
     return step, optimizer, scheduler
+
+
+def gather_fsdp_state_dicts(model, optimizer) -> tuple[dict, dict]:
+    """Gather the full (unsharded) model and optimizer state dicts under FSDP.
+
+    `model.state_dict()` and `FSDP.optim_state_dict(...)` are cross-rank collectives, so this must be
+    called on *every* rank with the prepared (FSDP-wrapped) `model` and `optimizer`. With
+    `rank0_only=True` and `offload_to_cpu=True`, every rank runs the all-gather but only rank 0
+    materializes the full dicts (the others get empty dicts) and they are kept on CPU to bound GPU
+    memory. The returned optimizer state dict is keyed by parameter FQNs and is world-size
+    independent; `load_fsdp_optimizer_state` reshards it on resume.
+
+    Returns:
+        (model_state_dict, optim_state_dict): full dicts on rank 0, empty dicts on other ranks.
+    """
+    from torch.distributed.fsdp import (
+        FullOptimStateDictConfig,
+        FullStateDictConfig,
+        FullyShardedDataParallel as FSDP,  # noqa F401
+        StateDictType,
+    )
+
+    state_cfg = FullStateDictConfig(offload_to_cpu=True, rank0_only=True)
+    optim_cfg = FullOptimStateDictConfig(offload_to_cpu=True, rank0_only=True)
+    with FSDP.state_dict_type(model, StateDictType.FULL_STATE_DICT, state_cfg, optim_cfg):
+        model_state_dict = model.state_dict()
+        optim_state_dict = FSDP.optim_state_dict(model, optimizer)
+    return model_state_dict, optim_state_dict
+
+
+def load_fsdp_optimizer_state(model, optimizer, checkpoint_dir: Path) -> None:
+    """Load the FSDP optimizer state (saved as safetensors) and reshard it into the optimizer.
+
+    This is a cross-rank collective and must be called on every rank *after* `accelerator.prepare()`
+    with the prepared (FSDP-wrapped) `model` and `optimizer`. The saved state is the full,
+    world-size-independent optimizer state (keyed by parameter FQNs); `FSDP.optim_state_dict_to_load`
+    reshards it to the current FSDP topology, so resume on a different number of GPUs works.
+    """
+    from torch.distributed.fsdp import (
+        FullOptimStateDictConfig,
+        FullStateDictConfig,
+        FullyShardedDataParallel as FSDP,  # noqa F401
+        StateDictType,
+    )
+
+    # Every rank reads the same full state from the (shared) checkpoint dir, so rank0_only=False.
+    full_osd = load_optimizer_state_dict(checkpoint_dir / TRAINING_STATE_DIR)
+    state_cfg = FullStateDictConfig(rank0_only=False)
+    optim_cfg = FullOptimStateDictConfig(rank0_only=False)
+    with FSDP.state_dict_type(model, StateDictType.FULL_STATE_DICT, state_cfg, optim_cfg):
+        sharded_osd = FSDP.optim_state_dict_to_load(model=model, optim=optimizer, optim_state_dict=full_osd)
+    optimizer.load_state_dict(sharded_osd)

src/lerobot/common/wandb_utils.py

@@ -180,24 +180,26 @@ class WandBLogger:
                 self._wandb_custom_step_key.add(new_custom_key)
                 self._wandb.define_metric(new_custom_key, hidden=True)
 
+        batch_data = {}
         for k, v in d.items():
+            # Skip the custom step key here, it's added to the batch below.
+            if custom_step_key is not None and k == custom_step_key:
+                continue
+
             if not isinstance(v, (int | float | str)):
                 logging.warning(
                     f'WandB logging of key "{k}" was ignored as its type "{type(v)}" is not handled by this wrapper.'
                 )
                 continue
 
-            # Do not log the custom step key itself.
+            batch_data[f"{mode}/{k}"] = v
-            if self._wandb_custom_step_key is not None and k in self._wandb_custom_step_key:
-                continue
 
+        if batch_data:
             if custom_step_key is not None:
-                value_custom_step = d[custom_step_key]
+                batch_data[f"{mode}/{custom_step_key}"] = d[custom_step_key]
-                data = {f"{mode}/{k}": v, f"{mode}/{custom_step_key}": value_custom_step}
+                self._wandb.log(batch_data)
-                self._wandb.log(data)
+            else:
-                continue
+                self._wandb.log(data=batch_data, step=step)
-
-            self._wandb.log(data={f"{mode}/{k}": v}, step=step)
 
     def log_video(self, video_path: str, step: int, mode: str = "train"):
         if mode not in {"train", "eval"}:

src/lerobot/configs/policies.py

@@ -79,6 +79,8 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):  # type: igno
     # Either the repo ID of a model hosted on the Hub or a path to a directory containing weights
     # saved using `Policy.save_pretrained`. If not provided, the policy is initialized from scratch.
     pretrained_path: Path | None = None
+    # Optional Hub revision (commit hash, branch, or tag) to pin the pretrained model version.
+    pretrained_revision: str | None = None
 
     def __post_init__(self) -> None:
         if not self.device or not is_torch_device_available(self.device):

src/lerobot/configs/rewards.py

@@ -56,6 +56,8 @@ class RewardModelConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):
     device: str | None = None
 
     pretrained_path: str | None = None
+    # Optional Hub revision (commit hash, branch, or tag) to pin the pretrained reward model version.
+    pretrained_revision: str | None = None
 
     push_to_hub: bool = False
     repo_id: str | None = None

src/lerobot/datasets/aggregate.py

@@ -32,6 +32,7 @@ from .feature_utils import features_equal_for_merge, get_hf_features_from_featur
 from .io_utils import (
     get_file_size_in_mb,
     get_parquet_file_size_in_mb,
+    to_parquet_one_row_group_per_episode,
     to_parquet_with_hf_images,
     write_info,
     write_stats,
@@ -551,6 +552,7 @@ def aggregate_data(src_meta, dst_meta, data_idx, data_files_size_in_mb, chunk_si
             aggr_root=dst_meta.root,
             hf_features=hf_features,
             concatenate=concatenate_data,
+            one_row_group_per_episode=True,
         )
 
         # Record the mapping from source to actual destination
@@ -628,6 +630,7 @@ def append_or_create_parquet_file(
     aggr_root: Path = None,
     hf_features: datasets.Features | None = None,
     concatenate: bool = True,
+    one_row_group_per_episode: bool = False,
 ) -> tuple[dict[str, int], tuple[int, int]]:
     """Appends data to an existing parquet file or creates a new one based on size constraints.
 
@@ -645,6 +648,8 @@ def append_or_create_parquet_file(
         aggr_root: Root path for the aggregated dataset.
         hf_features: Optional HuggingFace Features schema for proper image typing.
         concatenate: When False, always rotate to a new file instead of appending to the current one.
+        one_row_group_per_episode: True for DATA parquet (emit one row group per episode); False for
+            the episodes-metadata parquet (already one row per episode).
 
     Returns:
         tuple: (updated_idx, (dst_chunk, dst_file)) where updated_idx is the index dict
@@ -657,6 +662,8 @@ def append_or_create_parquet_file(
         dst_path.parent.mkdir(parents=True, exist_ok=True)
         if contains_images:
             to_parquet_with_hf_images(df, dst_path, features=hf_features)
+        elif one_row_group_per_episode:
+            to_parquet_one_row_group_per_episode(df, dst_path)
         else:
             df.to_parquet(dst_path)
         return idx, (dst_chunk, dst_file)
@@ -683,6 +690,8 @@ def append_or_create_parquet_file(
 
     if contains_images:
         to_parquet_with_hf_images(final_df, target_path, features=hf_features)
+    elif one_row_group_per_episode:
+        to_parquet_one_row_group_per_episode(final_df, target_path)
     else:
         final_df.to_parquet(target_path)
 

src/lerobot/datasets/dataset_metadata.py

@@ -15,6 +15,7 @@
 # limitations under the License.
 import contextlib
 from collections.abc import Callable
+from copy import deepcopy
 from pathlib import Path
 
 import numpy as np
@@ -709,7 +710,7 @@ class LeRobotDatasetMetadata:
 
         obj.root.mkdir(parents=True, exist_ok=False)
 
-        features = {**features, **DEFAULT_FEATURES}
+        features = {**deepcopy(features), **DEFAULT_FEATURES}
         _validate_feature_names(features)
 
         obj.tasks = None

src/lerobot/datasets/dataset_reader.py

@@ -74,6 +74,8 @@ class DatasetReader:
         self.episodes = episodes
         self._tolerance_s = tolerance_s
         self._video_backend = video_backend
+        if image_transforms is not None and not callable(image_transforms):
+            raise TypeError("image_transforms must be callable or None.")
         self._image_transforms = image_transforms
         self._return_uint8 = return_uint8
 
@@ -86,6 +88,16 @@ class DatasetReader:
             check_delta_timestamps(delta_timestamps, meta.fps, tolerance_s)
             self.delta_indices = get_delta_indices(delta_timestamps, meta.fps)
 
+    def set_image_transforms(self, image_transforms: Callable | None) -> None:
+        """Replace the transform applied to visual observations."""
+        if image_transforms is not None and not callable(image_transforms):
+            raise TypeError("image_transforms must be callable or None.")
+        self._image_transforms = image_transforms
+
+    def clear_image_transforms(self) -> None:
+        """Remove the transform applied to visual observations."""
+        self._image_transforms = None
+
     def try_load(self) -> bool:
         """Attempt to load from local cache. Returns True if data is sufficient."""
         try:

src/lerobot/datasets/dataset_tools.py

@@ -27,6 +27,7 @@ import logging
 import shutil
 from collections.abc import Callable
 from concurrent.futures import ProcessPoolExecutor, ThreadPoolExecutor, as_completed
+from copy import deepcopy
 from pathlib import Path
 
 import datasets
@@ -1101,7 +1102,9 @@ def _copy_episodes_metadata_and_stats(
     if dst_meta.video_keys and src_dataset.meta.video_keys:
         for key in dst_meta.video_keys:
             if key in src_dataset.meta.features:
-                dst_meta.info.features[key]["info"] = src_dataset.meta.info.features[key].get("info", {})
+                dst_meta.info.features[key]["info"] = deepcopy(
+                    src_dataset.meta.info.features[key].get("info", {})
+                )
 
     write_info(dst_meta.info, dst_meta.root)
 

src/lerobot/datasets/io_utils.py

@@ -20,6 +20,7 @@ import datasets
 import numpy as np
 import pandas
 import pandas as pd
+import pyarrow as pa
 import pyarrow.dataset as pa_ds
 import pyarrow.parquet as pq
 import torch
@@ -153,7 +154,7 @@ def cast_stats_to_numpy(stats: dict) -> dict[str, dict[str, np.ndarray]]:
     Returns:
         dict: The statistics dictionary with values cast to numpy arrays.
     """
-    stats = {key: np.array(value) for key, value in flatten_dict(stats).items()}
+    stats = {key: np.atleast_1d(np.array(value)) for key, value in flatten_dict(stats).items()}
     return unflatten_dict(stats)
 
 
@@ -270,21 +271,49 @@ def hf_transform_to_torch(items_dict: dict[str, list[Any]]) -> dict[str, list[to
     return items_dict
 
 
+def write_table_one_row_group_per_episode(table: pa.Table, path: Path) -> None:
+    """Write ``table`` with one parquet row group per episode (in episode order).
+
+    Keeps shards random-access friendly (``read_row_group(i)`` fetches episode i),
+    mirroring the recording writer. ``table`` must carry a contiguous
+    ``episode_index`` column.
+    """
+    episode_index = table.column("episode_index").to_numpy(zero_copy_only=False)
+    starts = np.concatenate(([0], np.nonzero(np.diff(episode_index))[0] + 1))
+    writer = pq.ParquetWriter(str(path), table.schema, compression="snappy", use_dictionary=True)
+    try:
+        for start, stop in zip(starts, np.append(starts[1:], len(episode_index)), strict=True):
+            writer.write_table(table.slice(start, stop - start))  # one episode -> one row group
+    finally:
+        writer.close()
+
+
 def to_parquet_with_hf_images(
     df: pandas.DataFrame, path: Path, features: datasets.Features | None = None
 ) -> None:
-    """This function correctly writes to parquet a panda DataFrame that contains images encoded by HF dataset.
+    """Write a DataFrame with HF-encoded images to parquet, one row group per episode.
-    This way, it can be loaded by HF dataset and correctly formatted images are returned.
 
-    Args:
+    Images are embedded into the arrow table first (``ParquetWriter.write_table``
-        df: DataFrame to write to parquet.
+    does not embed external image files like ``Dataset.to_parquet`` does).
-        path: Path to write the parquet file.
+    ``features`` types image columns as ``Image()`` in the parquet schema.
-        features: Optional HuggingFace Features schema. If provided, ensures image columns
-                  are properly typed as Image() in the parquet schema.
     """
-    # TODO(qlhoest): replace this weird synthax by `df.to_parquet(path)` only
     ds = datasets.Dataset.from_dict(df.to_dict(orient="list"), features=features)
-    ds.to_parquet(path)
+    ds = embed_images(ds)
+    table = ds.with_format("arrow")[:]
+    if "episode_index" in table.column_names:
+        write_table_one_row_group_per_episode(table, path)
+    else:
+        # No episode boundaries to align row groups to — keep a single write.
+        pq.write_table(table, str(path))
+
+
+def to_parquet_one_row_group_per_episode(df: pandas.DataFrame, path: Path) -> None:
+    """Write a (non-image) DataFrame to parquet with one row group per episode."""
+    table = pa.Table.from_pandas(df, preserve_index=False)
+    if "episode_index" in table.column_names:
+        write_table_one_row_group_per_episode(table, path)
+    else:
+        pq.write_table(table, str(path))
 
 
 def item_to_torch(item: dict) -> dict:

src/lerobot/datasets/lerobot_dataset.py

@@ -201,8 +201,6 @@ class LeRobotDataset(torch.utils.data.Dataset):
         super().__init__()
         self.repo_id = repo_id
         self._requested_root = Path(root) if root else None
-        self.reader = None
-        self.set_image_transforms(image_transforms)
         self.delta_timestamps = delta_timestamps
         self.tolerance_s = tolerance_s
         self.revision = revision if revision else CODEBASE_VERSION
@@ -249,6 +247,7 @@ class LeRobotDataset(torch.utils.data.Dataset):
             image_transforms=image_transforms,
             return_uint8=self._return_uint8,
         )
+        self.image_transforms = image_transforms
 
         # Load actual data
         if force_cache_sync or not self.reader.try_load():
@@ -505,15 +504,14 @@ class LeRobotDataset(torch.utils.data.Dataset):
 
     def set_image_transforms(self, image_transforms: Callable | None) -> None:
         """Replace the transform applied to visual observations."""
-        if image_transforms is not None and not callable(image_transforms):
+        self._ensure_reader().set_image_transforms(image_transforms)
-            raise TypeError("image_transforms must be callable or None.")
         self.image_transforms = image_transforms
-        if self.reader is not None:
-            self.reader._image_transforms = image_transforms
 
     def clear_image_transforms(self) -> None:
         """Remove the transform applied to visual observations."""
-        self.set_image_transforms(None)
+        if self.reader is not None:
+            self.reader.set_image_transforms(None)
+        self.image_transforms = None
 
     # ── Hub methods (stay on facade) ──────────────────────────────────
 

src/lerobot/datasets/pipeline_features.py

@@ -70,19 +70,21 @@ def aggregate_pipeline_dataset_features(
     initial_features: dict[PipelineFeatureType, dict[str, Any]],
     *,
     use_videos: bool = True,
+    exclude_images: bool = False,
     patterns: Sequence[str] | None = None,
 ) -> dict[str, dict]:
     """
     Aggregates and filters pipeline features to create a dataset-ready features dictionary.
 
     This function transforms initial features using the pipeline, categorizes them as action or observations
-    (image or state), filters them based on `use_videos` and `patterns`, and finally
+    (image or state), filters them based on `exclude_images` and `patterns`, and finally
     formats them for use with a Hugging Face LeRobot Dataset.
 
     Args:
         pipeline: The DataProcessorPipeline to apply.
         initial_features: A dictionary of raw feature specs for actions and observations.
-        use_videos: If False, image features are excluded.
+        use_videos: Controls the storage dtype for image features. If True, images are stored as "video"; if False, they are stored as "image".
+        exclude_images: If True, image features are dropped entirely from the output.
         patterns: A sequence of regex patterns to filter action and state features.
                   Image features are not affected by this filter.
 
@@ -120,7 +122,7 @@ def aggregate_pipeline_dataset_features(
             )
 
             # 2. Apply filtering rules.
-            if is_image and not use_videos:
+            if is_image and exclude_images:
                 continue
             if not is_image and not should_keep(key, compiled_patterns):
                 continue

src/lerobot/envs/utils.py

@@ -126,6 +126,26 @@ def preprocess_observation(observations: dict[str, np.ndarray]) -> dict[str, Ten
     if "camera_obs" in observations:
         return_observations[f"{OBS_STR}.camera_obs"] = observations["camera_obs"]
 
+    # Pass through any remaining ndarray/tensor keys not already handled above,
+    # so env plugins can expose extra observation keys via get_env_processors().
+    _handled = {"pixels", "environment_state", "agent_pos", "robot_state", "policy", "camera_obs"}
+    for key, value in observations.items():
+        if key in _handled:
+            continue
+        target = f"{OBS_STR}.{key}"
+        if target in return_observations:
+            continue
+        if isinstance(value, np.ndarray):
+            val = torch.from_numpy(value).float()
+            if val.dim() == 1:
+                val = val.unsqueeze(0)
+            return_observations[target] = val
+        elif isinstance(value, Tensor):
+            val = value.float()
+            if val.dim() == 1:
+                val = val.unsqueeze(0)
+            return_observations[target] = val
+
     return return_observations
 
 

src/lerobot/optim/__init__.py

@@ -20,6 +20,7 @@ from .optimizers import (
     SGDConfig as SGDConfig,
     XVLAAdamWConfig as XVLAAdamWConfig,
     load_optimizer_state,
+    load_optimizer_state_dict,
     save_optimizer_state,
 )
 from .schedulers import (
@@ -50,6 +51,7 @@ __all__ = [
     "VQBeTSchedulerConfig",
     # State management
     "load_optimizer_state",
+    "load_optimizer_state_dict",
     "load_scheduler_state",
     "save_optimizer_state",
     "save_scheduler_state",

src/lerobot/optim/optimizers.py

@@ -27,7 +27,7 @@ from lerobot.utils.constants import (
     OPTIMIZER_PARAM_GROUPS,
     OPTIMIZER_STATE,
 )
-from lerobot.utils.io_utils import deserialize_json_into_object, write_json
+from lerobot.utils.io_utils import deserialize_json_into_object, load_json, write_json
 from lerobot.utils.utils import flatten_dict, unflatten_dict
 
 # Type alias for parameters accepted by optimizer build() methods.
@@ -281,28 +281,37 @@ class MultiAdamConfig(OptimizerConfig):
 
 
 def save_optimizer_state(
-    optimizer: torch.optim.Optimizer | dict[str, torch.optim.Optimizer], save_dir: Path
+    optimizer: torch.optim.Optimizer | dict[str, torch.optim.Optimizer],
+    save_dir: Path,
+    optim_state_dict: dict | None = None,
 ) -> None:
     """Save optimizer state to disk.
 
     Args:
         optimizer: Either a single optimizer or a dictionary of optimizers.
         save_dir: Directory to save the optimizer state.
+        optim_state_dict: Pre-gathered optimizer state dict (for FSDP, where the sharded state must
+            be gathered across ranks first). If provided, it is saved directly instead of calling
+            ``optimizer.state_dict()``. Only supported for a single optimizer. Defaults to None.
     """
     if isinstance(optimizer, dict):
         # Handle dictionary of optimizers
+        if optim_state_dict is not None:
+            raise ValueError("optim_state_dict is not supported for a dict of optimizers")
         for name, opt in optimizer.items():
             optimizer_dir = save_dir / name
             optimizer_dir.mkdir(exist_ok=True, parents=True)
             _save_single_optimizer_state(opt, optimizer_dir)
     else:
         # Handle single optimizer
-        _save_single_optimizer_state(optimizer, save_dir)
+        _save_single_optimizer_state(optimizer, save_dir, optim_state_dict=optim_state_dict)
 
 
-def _save_single_optimizer_state(optimizer: torch.optim.Optimizer, save_dir: Path) -> None:
+def _save_single_optimizer_state(
+    optimizer: torch.optim.Optimizer, save_dir: Path, optim_state_dict: dict | None = None
+) -> None:
     """Save a single optimizer's state to disk."""
-    state = optimizer.state_dict()
+    state = dict(optim_state_dict) if optim_state_dict is not None else optimizer.state_dict()
     param_groups = state.pop("param_groups")
     flat_state = flatten_dict(state)
     save_file(flat_state, save_dir / OPTIMIZER_STATE)
@@ -356,3 +365,19 @@ def _load_single_optimizer_state(optimizer: torch.optim.Optimizer, save_dir: Pat
 
     optimizer.load_state_dict(loaded_state_dict)
     return optimizer
+
+
+def load_optimizer_state_dict(save_dir: Path) -> dict:
+    """Read a saved optimizer state dict (safetensors + json) back into a plain dict.
+
+    Unlike `load_optimizer_state`, this does not load into an optimizer and preserves the original
+    ``state`` keys verbatim (e.g. FSDP parameter FQNs, which are not integer-castable). It is used by
+    the FSDP resume path, where the full state must be resharded via `FSDP.optim_state_dict_to_load`
+    before being loaded into the (sharded) optimizer.
+    """
+    flat_state = load_file(save_dir / OPTIMIZER_STATE)
+    state = unflatten_dict(flat_state)
+    return {
+        "state": state.get("state", {}),
+        "param_groups": load_json(save_dir / OPTIMIZER_PARAM_GROUPS),
+    }

src/lerobot/policies/act/modeling_act.py

@@ -148,7 +148,7 @@ class ACTPolicy(PreTrainedPolicy):
         l1_loss = (abs_err * valid_mask).sum() / num_valid.clamp_min(1)
 
         loss_dict = {"l1_loss": l1_loss.item()}
-        if self.config.use_vae:
+        if self.config.use_vae and log_sigma_x2_hat is not None:
             # Calculate Dₖₗ(latent_pdf || standard_normal). Note: After computing the KL-divergence for
             # each dimension independently, we sum over the latent dimension to get the total
             # KL-divergence per batch element, then take the mean over the batch.

src/lerobot/policies/diffusion/modeling_diffusion.py

@@ -101,11 +101,23 @@ class DiffusionPolicy(PreTrainedPolicy):
 
     @torch.no_grad()
     def predict_action_chunk(self, batch: dict[str, Tensor], noise: Tensor | None = None) -> Tensor:
-        """Predict a chunk of actions given environment observations."""
+        """Predict a chunk of actions given environment observations.
-        # stack n latest observations from the queue
-        batch = {k: torch.stack(list(self._queues[k]), dim=1) for k in batch if k in self._queues}
-        actions = self.diffusion.generate_actions(batch, noise=noise)
 
+        Supports two modes:
+        - Online (queues populated via select_action): stacks observations from internal queues.
+        - Offline (empty queues, e.g. dataloader batch): uses the batch directly.
+        """
+        queues_populated = any(len(q) > 0 for q in self._queues.values())
+        if queues_populated:
+            batch = {k: torch.stack(list(self._queues[k]), dim=1) for k in batch if k in self._queues}
+        else:
+            batch = dict(batch)
+            if self.config.image_features:
+                for key in self.config.image_features:
+                    if batch[key].ndim == 4:
+                        batch[key] = batch[key].unsqueeze(1)
+                batch[OBS_IMAGES] = torch.stack([batch[key] for key in self.config.image_features], dim=-4)
+        actions = self.diffusion.generate_actions(batch, noise=noise)
         return actions
 
     @torch.no_grad()

src/lerobot/policies/factory.py

@@ -252,6 +252,7 @@ class ProcessorConfigKwargs(TypedDict, total=False):
 def make_pre_post_processors(
     policy_cfg: PreTrainedConfig,
     pretrained_path: str | None = None,
+    pretrained_revision: str | None = None,
     **kwargs: Unpack[ProcessorConfigKwargs],
 ) -> tuple[
     PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
@@ -309,6 +310,7 @@ def make_pre_post_processors(
             overrides=kwargs.get("preprocessor_overrides", {}),
             to_transition=batch_to_transition,
             to_output=transition_to_batch,
+            revision=pretrained_revision,
         )
         postprocessor = PolicyProcessorPipeline.from_pretrained(
             pretrained_model_name_or_path=pretrained_path,
@@ -318,6 +320,7 @@ def make_pre_post_processors(
             overrides=kwargs.get("postprocessor_overrides", {}),
             to_transition=policy_action_to_transition,
             to_output=transition_to_policy_action,
+            revision=pretrained_revision,
         )
         _reconnect_relative_absolute_steps(preprocessor, postprocessor)
         return preprocessor, postprocessor
@@ -557,6 +560,7 @@ def make_policy(
         # Load a pretrained policy and override the config if needed (for example, if there are inference-time
         # hyperparameters that we want to vary).
         kwargs["pretrained_name_or_path"] = cfg.pretrained_path
+        kwargs["revision"] = cfg.pretrained_revision
         policy = policy_cls.from_pretrained(**kwargs)
     elif cfg.pretrained_path and cfg.use_peft:
         # Load a pretrained PEFT model on top of the policy. The pretrained path points to the folder/repo

src/lerobot/policies/pretrained.py

@@ -23,7 +23,7 @@ from typing import TypedDict, TypeVar, Unpack
 
 import packaging
 import safetensors
-from huggingface_hub import HfApi, ModelCard, ModelCardData, hf_hub_download
+from huggingface_hub import HfApi, ModelCard, ModelCardData, hf_hub_download, save_torch_state_dict
 from huggingface_hub.constants import SAFETENSORS_SINGLE_FILE
 from huggingface_hub.errors import HfHubHTTPError
 from safetensors.torch import load_model as load_model_as_safetensor, save_model as save_model_as_safetensor
@@ -129,10 +129,43 @@ class PreTrainedPolicy(nn.Module, HubMixin, abc.ABC):
         if not getattr(cls, "name", None):
             raise TypeError(f"Class {cls.__name__} must define 'name'")
 
-    def _save_pretrained(self, save_directory: Path) -> None:
+    def save_pretrained(
+        self,
+        save_directory: str | Path,
+        *,
+        state_dict: dict[str, Tensor] | None = None,
+        repo_id: str | None = None,
+        push_to_hub: bool = False,
+        card_kwargs: dict | None = None,
+        **push_to_hub_kwargs,
+    ) -> str | None:
+        """Save the policy to a directory (and optionally push to the Hub).
+
+        Overrides `HubMixin.save_pretrained` to add a `state_dict` argument (mirroring
+        `transformers.PreTrainedModel.save_pretrained`). Under FSDP, `self.state_dict()` would
+        return sharded tensors, so the caller gathers the full state dict via a cross-rank
+        collective and passes it here for `_save_pretrained` to write directly.
+        """
+        save_directory = Path(save_directory)
+        save_directory.mkdir(parents=True, exist_ok=True)
+        self._save_pretrained(save_directory, state_dict=state_dict)
+        if push_to_hub:
+            if repo_id is None:
+                repo_id = save_directory.name
+            return self.push_to_hub(repo_id=repo_id, card_kwargs=card_kwargs, **push_to_hub_kwargs)
+        return None
+
+    def _save_pretrained(self, save_directory: Path, state_dict: dict[str, Tensor] | None = None) -> None:
         self.config._save_pretrained(save_directory)
         model_to_save = self.module if hasattr(self, "module") else self
-        save_model_as_safetensor(model_to_save, str(save_directory / SAFETENSORS_SINGLE_FILE))
+        if state_dict is None:
+            save_model_as_safetensor(model_to_save, str(save_directory / SAFETENSORS_SINGLE_FILE))
+            return
+        # A pre-gathered (e.g. FSDP full) state dict was supplied: write it directly.
+        # `save_torch_state_dict` discards shared-tensor duplicates just like `save_model` does;
+        # pin `max_shard_size` above the total size so the output stays a single `model.safetensors`
+        total_bytes = sum(t.numel() * t.element_size() for t in state_dict.values())
+        save_torch_state_dict(state_dict, str(save_directory), max_shard_size=max(total_bytes, 1))
 
     @classmethod
     def from_pretrained(
@@ -270,6 +303,7 @@ class PreTrainedPolicy(nn.Module, HubMixin, abc.ABC):
         self,
         cfg: TrainPipelineConfig,
         peft_model=None,
+        state_dict: dict[str, Tensor] | None = None,
     ):
         api = HfApi()
         repo_id = api.create_repo(
@@ -287,7 +321,8 @@ class PreTrainedPolicy(nn.Module, HubMixin, abc.ABC):
                 peft_model.save_pretrained(saved_path)
                 self.config.save_pretrained(saved_path)
             else:
-                self.save_pretrained(saved_path)  # Calls _save_pretrained and stores model tensors
+                # Calls _save_pretrained and stores model tensors
+                self.save_pretrained(saved_path, state_dict=state_dict)
 
             card = self.generate_model_card(
                 cfg.dataset.repo_id, self.config.type, self.config.license, self.config.tags, cfg=cfg

src/lerobot/rewards/factory.py

@@ -124,6 +124,7 @@ def make_reward_model(cfg: RewardModelConfig, **kwargs) -> PreTrainedRewardModel
 
     if cfg.pretrained_path:
         kwargs["pretrained_name_or_path"] = cfg.pretrained_path
+        kwargs["revision"] = cfg.pretrained_revision
         reward_model = reward_cls.from_pretrained(**kwargs)
     else:
         reward_model = reward_cls(**kwargs)

src/lerobot/robots/bi_openarm_follower/bi_openarm_follower.py

@@ -18,7 +18,8 @@ import logging
 from functools import cached_property
 
 from lerobot.types import RobotAction, RobotObservation
-from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
 
 from ..openarm_follower import OpenArmFollower, OpenArmFollowerConfig
 from ..robot import Robot
@@ -27,7 +28,7 @@ from .config_bi_openarm_follower import BiOpenArmFollowerConfig
 logger = logging.getLogger(__name__)
 
 
-class BiOpenArmFollower(Robot):
+class BiOpenArmFollower(BimanualMixin, Robot):
     """
     Bimanual OpenArm Follower Arms
     """
@@ -39,15 +40,17 @@ class BiOpenArmFollower(Robot):
         super().__init__(config)
         self.config = config
 
-        # Top-level cameras are distributed evenly: each arm's OpenArmFollower
+        # Top-level cameras are opened by `left_arm` for convenience, but their
-        # will only open the cameras assigned to it. Per-arm cameras are used
+        # keys stay unprefixed in observations (tracked via `_top_level_cam_keys`).
-        # as fallback when top-level cameras are empty.
+        self._top_level_cam_keys = set(config.cameras)
-        if config.cameras:
+        _collisions = self._top_level_cam_keys & set(
-            left_cameras = config.cameras
+            config.left_arm_config.cameras
-            right_cameras = {}
+        ) | self._top_level_cam_keys & set(config.right_arm_config.cameras)
-        else:
+        if _collisions:
-            left_cameras = config.left_arm_config.cameras
+            raise ValueError(
-            right_cameras = config.right_arm_config.cameras
+                f"Top-level camera names collide with per-arm camera names: {sorted(_collisions)}"
+            )
+        left_arm_cameras = {**config.left_arm_config.cameras, **config.cameras}
 
         left_arm_config = OpenArmFollowerConfig(
             id=f"{config.id}_left" if config.id else None,
@@ -56,7 +59,7 @@ class BiOpenArmFollower(Robot):
             disable_torque_on_disconnect=config.left_arm_config.disable_torque_on_disconnect,
             use_velocity_and_torque=config.left_arm_config.use_velocity_and_torque,
             max_relative_target=config.left_arm_config.max_relative_target,
-            cameras=left_cameras,
+            cameras=left_arm_cameras,
             side=config.left_arm_config.side,
             can_interface=config.left_arm_config.can_interface,
             use_can_fd=config.left_arm_config.use_can_fd,
@@ -75,7 +78,7 @@ class BiOpenArmFollower(Robot):
             disable_torque_on_disconnect=config.right_arm_config.disable_torque_on_disconnect,
             use_velocity_and_torque=config.right_arm_config.use_velocity_and_torque,
             max_relative_target=config.right_arm_config.max_relative_target,
-            cameras=right_cameras,
+            cameras=config.right_arm_config.cameras,
             side=config.right_arm_config.side,
             can_interface=config.right_arm_config.can_interface,
             use_can_fd=config.right_arm_config.use_can_fd,
@@ -95,22 +98,19 @@ class BiOpenArmFollower(Robot):
 
     @property
     def _motors_ft(self) -> dict[str, type]:
-        left_arm_motors_ft = self.left_arm._motors_ft
-        right_arm_motors_ft = self.right_arm._motors_ft
-
-        # Right first, then left — matches the teleoperator (OpenArmMini) ordering
-        # and the dataset feature names recorded during data collection.
         return {
-            **{f"right_{k}": v for k, v in right_arm_motors_ft.items()},
+            **{f"left_{k}": v for k, v in self.left_arm._motors_ft.items()},
-            **{f"left_{k}": v for k, v in left_arm_motors_ft.items()},
+            **{f"right_{k}": v for k, v in self.right_arm._motors_ft.items()},
         }
 
     @property
     def _cameras_ft(self) -> dict[str, tuple]:
-        # Cameras already have unique user-chosen names (e.g. "left_wrist", "base",
+        out: dict[str, tuple] = {}
-        # "right_wrist"), so we merge them directly — unlike motors which need the
+        for k, v in self.left_arm._cameras_ft.items():
-        # left_/right_ prefix to disambiguate identical per-arm joint names.
+            out[k if k in self._top_level_cam_keys else f"left_{k}"] = v
-        return {**self.left_arm._cameras_ft, **self.right_arm._cameras_ft}
+        for k, v in self.right_arm._cameras_ft.items():
+            out[f"right_{k}"] = v
+        return out
 
     @cached_property
     def observation_features(self) -> dict[str, type | tuple]:
@@ -120,27 +120,6 @@ class BiOpenArmFollower(Robot):
     def action_features(self) -> dict[str, type]:
         return self._motors_ft
 
-    @property
-    def is_connected(self) -> bool:
-        return self.left_arm.is_connected and self.right_arm.is_connected
-
-    @check_if_already_connected
-    def connect(self, calibrate: bool = True) -> None:
-        self.left_arm.connect(calibrate)
-        self.right_arm.connect(calibrate)
-
-    @property
-    def is_calibrated(self) -> bool:
-        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
-
-    def calibrate(self) -> None:
-        self.left_arm.calibrate()
-        self.right_arm.calibrate()
-
-    def configure(self) -> None:
-        self.left_arm.configure()
-        self.right_arm.configure()
-
     def setup_motors(self) -> None:
         raise NotImplementedError(
             "Motor ID configuration is typically done via manufacturer tools for CAN motors."
@@ -148,21 +127,15 @@ class BiOpenArmFollower(Robot):
 
     @check_if_not_connected
     def get_observation(self) -> RobotObservation:
-        obs_dict = {}
+        obs_dict: RobotObservation = {}
 
-        # Camera keys that should NOT get the arm prefix (they already have unique names)
+        # Add "left_" prefix to per-arm keys; keep top-level camera keys unprefixed.
-        left_cam_keys = set(self.left_arm.cameras.keys())
+        for key, value in self.left_arm.get_observation().items():
-        right_cam_keys = set(self.right_arm.cameras.keys())
+            obs_dict[key if key in self._top_level_cam_keys else f"left_{key}"] = value
 
-        # Right first, then left — matches the teleoperator (OpenArmMini) ordering
+        # Add "right_" prefix
-        # and the dataset feature names recorded during data collection.
+        for key, value in self.right_arm.get_observation().items():
-        right_obs = self.right_arm.get_observation()
+            obs_dict[f"right_{key}"] = value
-        for key, value in right_obs.items():
-            obs_dict[key if key in right_cam_keys else f"right_{key}"] = value
-
-        left_obs = self.left_arm.get_observation()
-        for key, value in left_obs.items():
-            obs_dict[key if key in left_cam_keys else f"left_{key}"] = value
 
         return obs_dict
 
@@ -189,9 +162,4 @@ class BiOpenArmFollower(Robot):
         prefixed_sent_action_left = {f"left_{key}": value for key, value in sent_action_left.items()}
         prefixed_sent_action_right = {f"right_{key}": value for key, value in sent_action_right.items()}
 
-        return {**prefixed_sent_action_right, **prefixed_sent_action_left}
+        return {**prefixed_sent_action_left, **prefixed_sent_action_right}
-
-    @check_if_not_connected
-    def disconnect(self):
-        self.left_arm.disconnect()
-        self.right_arm.disconnect()

src/lerobot/robots/bi_openarm_follower/config_bi_openarm_follower.py

@@ -32,5 +32,7 @@ class BiOpenArmFollowerConfig(RobotConfig):
     left_arm_config: OpenArmFollowerConfigBase
     right_arm_config: OpenArmFollowerConfigBase
 
-    # Top-level cameras shared across both arms.
+    # Top-level cameras not attached to a specific side. Keys are kept as-is in
+    # observations (no `left_`/`right_` prefix). Per-arm cameras (declared on
+    # `{left,right}_arm_config.cameras`) are prefixed.
     cameras: dict[str, CameraConfig] = field(default_factory=dict)

src/lerobot/robots/bi_rebot_b601_follower/bi_rebot_b601_follower.py

@@ -18,7 +18,8 @@ import logging
 from functools import cached_property
 
 from lerobot.types import RobotAction, RobotObservation
-from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
 
 from ..rebot_b601_follower import RebotB601Follower, RebotB601FollowerRobotConfig
 from ..robot import Robot
@@ -27,7 +28,7 @@ from .config_bi_rebot_b601_follower import BiRebotB601FollowerConfig
 logger = logging.getLogger(__name__)
 
 
-class BiRebotB601Follower(Robot):
+class BiRebotB601Follower(BimanualMixin, Robot):
     """Bimanual Seeed Studio reBot B601-DM follower.
 
     Composes two single-arm :class:`RebotB601Follower` instances. Observation and
@@ -41,6 +42,18 @@ class BiRebotB601Follower(Robot):
         super().__init__(config)
         self.config = config
 
+        # Top-level cameras are opened by `left_arm` for convenience, but their
+        # keys stay unprefixed in observations (tracked via `_top_level_cam_keys`).
+        self._top_level_cam_keys = set(config.cameras)
+        _collisions = self._top_level_cam_keys & set(
+            config.left_arm_config.cameras
+        ) | self._top_level_cam_keys & set(config.right_arm_config.cameras)
+        if _collisions:
+            raise ValueError(
+                f"Top-level camera names collide with per-arm camera names: {sorted(_collisions)}"
+            )
+        left_arm_cameras = {**config.left_arm_config.cameras, **config.cameras}
+
         left_arm_config = RebotB601FollowerRobotConfig(
             id=f"{config.id}_left" if config.id else None,
             calibration_dir=config.calibration_dir,
@@ -49,7 +62,7 @@ class BiRebotB601Follower(Robot):
             dm_serial_baud=config.left_arm_config.dm_serial_baud,
             disable_torque_on_disconnect=config.left_arm_config.disable_torque_on_disconnect,
             max_relative_target=config.left_arm_config.max_relative_target,
-            cameras=config.left_arm_config.cameras,
+            cameras=left_arm_cameras,
             motor_can_ids=config.left_arm_config.motor_can_ids,
             pos_vel_velocity=config.left_arm_config.pos_vel_velocity,
             gripper_torque_ratio=config.left_arm_config.gripper_torque_ratio,
@@ -86,10 +99,12 @@ class BiRebotB601Follower(Robot):
 
     @property
     def _cameras_ft(self) -> dict[str, tuple]:
-        return {
+        out: dict[str, tuple] = {}
-            **{f"left_{k}": v for k, v in self.left_arm._cameras_ft.items()},
+        for k, v in self.left_arm._cameras_ft.items():
-            **{f"right_{k}": v for k, v in self.right_arm._cameras_ft.items()},
+            out[k if k in self._top_level_cam_keys else f"left_{k}"] = v
-        }
+        for k, v in self.right_arm._cameras_ft.items():
+            out[f"right_{k}"] = v
+        return out
 
     @cached_property
     def observation_features(self) -> dict[str, type | tuple]:
@@ -99,32 +114,13 @@ class BiRebotB601Follower(Robot):
     def action_features(self) -> dict[str, type]:
         return self._motors_ft
 
-    @property
-    def is_connected(self) -> bool:
-        return self.left_arm.is_connected and self.right_arm.is_connected
-
-    @check_if_already_connected
-    def connect(self, calibrate: bool = True) -> None:
-        self.left_arm.connect(calibrate)
-        self.right_arm.connect(calibrate)
-
-    @property
-    def is_calibrated(self) -> bool:
-        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
-
-    def calibrate(self) -> None:
-        self.left_arm.calibrate()
-        self.right_arm.calibrate()
-
-    def configure(self) -> None:
-        self.left_arm.configure()
-        self.right_arm.configure()
-
     @check_if_not_connected
     def get_observation(self) -> RobotObservation:
-        obs_dict = {}
+        obs_dict: RobotObservation = {}
-        obs_dict.update({f"left_{k}": v for k, v in self.left_arm.get_observation().items()})
+        for k, v in self.left_arm.get_observation().items():
-        obs_dict.update({f"right_{k}": v for k, v in self.right_arm.get_observation().items()})
+            obs_dict[k if k in self._top_level_cam_keys else f"left_{k}"] = v
+        for k, v in self.right_arm.get_observation().items():
+            obs_dict[f"right_{k}"] = v
         return obs_dict
 
     @check_if_not_connected
@@ -143,8 +139,3 @@ class BiRebotB601Follower(Robot):
             **{f"left_{k}": v for k, v in sent_action_left.items()},
             **{f"right_{k}": v for k, v in sent_action_right.items()},
         }
-
-    @check_if_not_connected
-    def disconnect(self) -> None:
-        self.left_arm.disconnect()
-        self.right_arm.disconnect()

src/lerobot/robots/bi_rebot_b601_follower/config_bi_rebot_b601_follower.py

@@ -14,7 +14,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from dataclasses import dataclass
+from dataclasses import dataclass, field
+
+from lerobot.cameras import CameraConfig
 
 from ..config import RobotConfig
 from ..rebot_b601_follower import RebotB601FollowerConfig
@@ -27,3 +29,8 @@ class BiRebotB601FollowerConfig(RobotConfig):
 
     left_arm_config: RebotB601FollowerConfig
     right_arm_config: RebotB601FollowerConfig
+
+    # Top-level cameras not attached to a specific side. Keys are kept as-is in
+    # observations (no `left_`/`right_` prefix). Per-arm cameras (declared on
+    # `{left,right}_arm_config.cameras`) are prefixed.
+    cameras: dict[str, CameraConfig] = field(default_factory=dict)

src/lerobot/robots/bi_so_follower/bi_so_follower.py

@@ -18,7 +18,8 @@ import logging
 from functools import cached_property
 
 from lerobot.types import RobotAction, RobotObservation
-from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
 
 from ..robot import Robot
 from ..so_follower import SOFollower, SOFollowerRobotConfig
@@ -27,7 +28,7 @@ from .config_bi_so_follower import BiSOFollowerConfig
 logger = logging.getLogger(__name__)
 
 
-class BiSOFollower(Robot):
+class BiSOFollower(BimanualMixin, Robot):
     """
     [Bimanual SO Follower Arms](https://github.com/TheRobotStudio/SO-ARM100) designed by TheRobotStudio
     """
@@ -39,6 +40,18 @@ class BiSOFollower(Robot):
         super().__init__(config)
         self.config = config
 
+        # Top-level cameras are opened by `left_arm` for convenience, but their
+        # keys stay unprefixed in observations (tracked via `_top_level_cam_keys`).
+        self._top_level_cam_keys = set(config.cameras)
+        _collisions = self._top_level_cam_keys & set(
+            config.left_arm_config.cameras
+        ) | self._top_level_cam_keys & set(config.right_arm_config.cameras)
+        if _collisions:
+            raise ValueError(
+                f"Top-level camera names collide with per-arm camera names: {sorted(_collisions)}"
+            )
+        left_arm_cameras = {**config.left_arm_config.cameras, **config.cameras}
+
         left_arm_config = SOFollowerRobotConfig(
             id=f"{config.id}_left" if config.id else None,
             calibration_dir=config.calibration_dir,
@@ -46,7 +59,7 @@ class BiSOFollower(Robot):
             disable_torque_on_disconnect=config.left_arm_config.disable_torque_on_disconnect,
             max_relative_target=config.left_arm_config.max_relative_target,
             use_degrees=config.left_arm_config.use_degrees,
-            cameras=config.left_arm_config.cameras,
+            cameras=left_arm_cameras,
         )
 
         right_arm_config = SOFollowerRobotConfig(
@@ -77,13 +90,12 @@ class BiSOFollower(Robot):
 
     @property
     def _cameras_ft(self) -> dict[str, tuple]:
-        left_arm_cameras_ft = self.left_arm._cameras_ft
+        out: dict[str, tuple] = {}
-        right_arm_cameras_ft = self.right_arm._cameras_ft
+        for k, v in self.left_arm._cameras_ft.items():
-
+            out[k if k in self._top_level_cam_keys else f"left_{k}"] = v
-        return {
+        for k, v in self.right_arm._cameras_ft.items():
-            **{f"left_{k}": v for k, v in left_arm_cameras_ft.items()},
+            out[f"right_{k}"] = v
-            **{f"right_{k}": v for k, v in right_arm_cameras_ft.items()},
+        return out
-        }
 
     @cached_property
     def observation_features(self) -> dict[str, type | tuple]:
@@ -93,42 +105,21 @@ class BiSOFollower(Robot):
     def action_features(self) -> dict[str, type]:
         return self._motors_ft
 
-    @property
-    def is_connected(self) -> bool:
-        return self.left_arm.is_connected and self.right_arm.is_connected
-
-    @check_if_already_connected
-    def connect(self, calibrate: bool = True) -> None:
-        self.left_arm.connect(calibrate)
-        self.right_arm.connect(calibrate)
-
-    @property
-    def is_calibrated(self) -> bool:
-        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
-
-    def calibrate(self) -> None:
-        self.left_arm.calibrate()
-        self.right_arm.calibrate()
-
-    def configure(self) -> None:
-        self.left_arm.configure()
-        self.right_arm.configure()
-
     def setup_motors(self) -> None:
         self.left_arm.setup_motors()
         self.right_arm.setup_motors()
 
     @check_if_not_connected
     def get_observation(self) -> RobotObservation:
-        obs_dict = {}
+        obs_dict: RobotObservation = {}
 
-        # Add "left_" prefix
+        # Add "left_" prefix to per-arm keys; keep top-level camera keys unprefixed.
-        left_obs = self.left_arm.get_observation()
+        for key, value in self.left_arm.get_observation().items():
-        obs_dict.update({f"left_{key}": value for key, value in left_obs.items()})
+            obs_dict[key if key in self._top_level_cam_keys else f"left_{key}"] = value
 
         # Add "right_" prefix
-        right_obs = self.right_arm.get_observation()
+        for key, value in self.right_arm.get_observation().items():
-        obs_dict.update({f"right_{key}": value for key, value in right_obs.items()})
+            obs_dict[f"right_{key}"] = value
 
         return obs_dict
 
@@ -151,8 +142,3 @@ class BiSOFollower(Robot):
         prefixed_sent_action_right = {f"right_{key}": value for key, value in sent_action_right.items()}
 
         return {**prefixed_sent_action_left, **prefixed_sent_action_right}
-
-    @check_if_not_connected
-    def disconnect(self):
-        self.left_arm.disconnect()
-        self.right_arm.disconnect()

src/lerobot/robots/bi_so_follower/config_bi_so_follower.py

@@ -14,7 +14,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from dataclasses import dataclass
+from dataclasses import dataclass, field
+
+from lerobot.cameras import CameraConfig
 
 from ..config import RobotConfig
 from ..so_follower import SOFollowerConfig
@@ -27,3 +29,8 @@ class BiSOFollowerConfig(RobotConfig):
 
     left_arm_config: SOFollowerConfig
     right_arm_config: SOFollowerConfig
+
+    # Top-level cameras not attached to a specific side. Keys are kept as-is in
+    # observations (no `left_`/`right_` prefix). Per-arm cameras (declared on
+    # `{left,right}_arm_config.cameras`) are prefixed.
+    cameras: dict[str, CameraConfig] = field(default_factory=dict)

src/lerobot/scripts/lerobot_calibrate.py

@@ -54,6 +54,7 @@ from lerobot.teleoperators import (  # noqa: F401
     Teleoperator,
     TeleoperatorConfig,
     bi_openarm_leader,
+    bi_openarm_mini,
     bi_rebot_102_leader,
     bi_so_leader,
     homunculus,

src/lerobot/scripts/lerobot_find_joint_limits.py

@@ -57,6 +57,7 @@ from lerobot.robots import (  # noqa: F401
 from lerobot.teleoperators import (  # noqa: F401
     TeleoperatorConfig,
     bi_openarm_leader,
+    bi_openarm_mini,
     bi_rebot_102_leader,
     bi_so_leader,
     gamepad,

src/lerobot/scripts/lerobot_record.py

@@ -137,6 +137,7 @@ from lerobot.teleoperators import (  # noqa: F401
     Teleoperator,
     TeleoperatorConfig,
     bi_openarm_leader,
+    bi_openarm_mini,
     bi_rebot_102_leader,
     bi_so_leader,
     homunculus,

src/lerobot/scripts/lerobot_rollout.py

@@ -174,6 +174,7 @@ from lerobot.teleoperators import (  # noqa: F401
     Teleoperator,
     TeleoperatorConfig,
     bi_openarm_leader,
+    bi_openarm_mini,
     bi_rebot_102_leader,
     bi_so_leader,
     homunculus,

src/lerobot/scripts/lerobot_setup_motors.py

@@ -41,6 +41,7 @@ from lerobot.robots import (  # noqa: F401
 )
 from lerobot.teleoperators import (  # noqa: F401
     TeleoperatorConfig,
+    bi_openarm_mini,
     bi_rebot_102_leader,
     bi_so_leader,
     koch_leader,

src/lerobot/scripts/lerobot_teleoperate.py

@@ -89,6 +89,7 @@ from lerobot.teleoperators import (  # noqa: F401
     Teleoperator,
     TeleoperatorConfig,
     bi_openarm_leader,
+    bi_openarm_mini,
     bi_rebot_102_leader,
     bi_so_leader,
     gamepad,

src/lerobot/scripts/lerobot_train.py

@@ -34,8 +34,10 @@ from torch.optim import Optimizer
 from tqdm import tqdm
 
 from lerobot.common.train_utils import (
+    gather_fsdp_state_dicts,
     get_step_checkpoint_dir,
     get_step_identifier,
+    load_fsdp_optimizer_state,
     load_training_batch_size,
     load_training_num_processes,
     load_training_state,
@@ -189,6 +191,7 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
 
     require_package("accelerate", extra="training")
     from accelerate import Accelerator
+    from accelerate.utils import DistributedDataParallelKwargs, DistributedType
 
     cfg.validate()
 
@@ -197,8 +200,6 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
     # We set step_scheduler_with_optimizer=False to prevent accelerate from adjusting the lr_scheduler steps based on the num_processes
     # We set find_unused_parameters=True to handle models with conditional computation
     if accelerator is None:
-        from accelerate.utils import DistributedDataParallelKwargs
-
         ddp_kwargs = DistributedDataParallelKwargs(find_unused_parameters=True)
         # Accelerate auto-detects the device based on the available hardware and ignores the policy.device setting.
         # Force the device to be CPU when the active config's device is set to CPU (works for both policy and reward model training).
@@ -345,6 +346,7 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
         preprocessor, postprocessor = make_pre_post_processors(
             policy_cfg=cfg.policy,
             pretrained_path=processor_pretrained_path,
+            pretrained_revision=getattr(cfg.policy, "pretrained_revision", None),
             **processor_kwargs,
         )
 
@@ -370,7 +372,12 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
     step = 0  # number of policy updates (forward + backward + optim)
 
     if cfg.resume:
-        step, optimizer, lr_scheduler = load_training_state(cfg.checkpoint_path, optimizer, lr_scheduler)
+        # Under FSDP the optimizer state is sharded and must be loaded after `accelerator.prepare()`
+        # (see load_fsdp_optimizer_state below), so skip the optimizer here and load it then.
+        is_fsdp = accelerator.distributed_type == DistributedType.FSDP
+        step, optimizer, lr_scheduler = load_training_state(
+            cfg.checkpoint_path, optimizer, lr_scheduler, load_optimizer=not is_fsdp
+        )
 
     num_learnable_params = sum(p.numel() for p in policy.parameters() if p.requires_grad)
     num_total_params = sum(p.numel() for p in policy.parameters())
@@ -460,6 +467,12 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
     policy, optimizer, dataloader, lr_scheduler = accelerator.prepare(
         policy, optimizer, dataloader, lr_scheduler
     )
+
+    # FSDP optimizer state is sharded across ranks, so it can only be loaded once the optimizer and
+    # model are FSDP-wrapped (i.e. after `prepare`). Collective: every rank must participate.
+    if cfg.resume and accelerator.distributed_type == DistributedType.FSDP:
+        load_fsdp_optimizer_state(policy, optimizer, cfg.checkpoint_path)
+
     dl_iter = cycle(dataloader)
 
     policy.train()
@@ -558,6 +571,14 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
             train_tracker.reset_averages()
 
         if cfg.save_checkpoint and is_saving_step:
+            # Under FSDP, gathering the full model + optimizer state dicts is a cross-rank collective,
+            # so all ranks must participate; rank 0 then writes the materialized dicts. For DDP /
+            # single-GPU the state dicts are saved the normal way inside save_checkpoint.
+            is_fsdp = accelerator.distributed_type == DistributedType.FSDP
+            if is_fsdp:
+                model_state_dict, optim_state_dict = gather_fsdp_state_dicts(policy, optimizer)
+            else:
+                model_state_dict, optim_state_dict = None, None
             if is_main_process:
                 logging.info(f"Checkpoint policy after step {step}")
                 checkpoint_dir = get_step_checkpoint_dir(cfg.output_dir, cfg.steps, step)
@@ -572,6 +593,8 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
                     postprocessor=postprocessor,
                     num_processes=accelerator.num_processes,
                     batch_size=cfg.batch_size,
+                    model_state_dict=model_state_dict,
+                    optim_state_dict=optim_state_dict,
                 )
                 update_last_checkpoint(checkpoint_dir)
                 if wandb_logger:
@@ -634,6 +657,8 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
     if eval_env:
         close_envs(eval_env)
 
+    is_fsdp = accelerator.distributed_type == DistributedType.FSDP
+    model_state_dict = accelerator.get_state_dict(policy) if is_fsdp else None
     if is_main_process:
         logging.info("End of training")
 
@@ -643,7 +668,7 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
             if not cfg.is_reward_model_training and cfg.policy.use_peft:
                 unwrapped_model.push_model_to_hub(cfg, peft_model=unwrapped_model)
             else:
-                unwrapped_model.push_model_to_hub(cfg)
+                unwrapped_model.push_model_to_hub(cfg, state_dict=model_state_dict)
             preprocessor.push_to_hub(active_cfg.repo_id)
             postprocessor.push_to_hub(active_cfg.repo_id)
 

src/lerobot/teleoperators/bi_openarm_leader/bi_openarm_leader.py

@@ -18,7 +18,8 @@ import logging
 from functools import cached_property
 
 from lerobot.types import RobotAction
-from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
 
 from ..openarm_leader import OpenArmLeader, OpenArmLeaderConfig
 from ..teleoperator import Teleoperator
@@ -27,7 +28,7 @@ from .config_bi_openarm_leader import BiOpenArmLeaderConfig
 logger = logging.getLogger(__name__)
 
 
-class BiOpenArmLeader(Teleoperator):
+class BiOpenArmLeader(BimanualMixin, Teleoperator):
     """
     Bimanual OpenArm Leader Arms
     """
@@ -86,27 +87,6 @@ class BiOpenArmLeader(Teleoperator):
     def feedback_features(self) -> dict[str, type]:
         return {}
 
-    @property
-    def is_connected(self) -> bool:
-        return self.left_arm.is_connected and self.right_arm.is_connected
-
-    @check_if_already_connected
-    def connect(self, calibrate: bool = True) -> None:
-        self.left_arm.connect(calibrate)
-        self.right_arm.connect(calibrate)
-
-    @property
-    def is_calibrated(self) -> bool:
-        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
-
-    def calibrate(self) -> None:
-        self.left_arm.calibrate()
-        self.right_arm.calibrate()
-
-    def configure(self) -> None:
-        self.left_arm.configure()
-        self.right_arm.configure()
-
     def setup_motors(self) -> None:
         raise NotImplementedError(
             "Motor ID configuration is typically done via manufacturer tools for CAN motors."
@@ -129,8 +109,3 @@ class BiOpenArmLeader(Teleoperator):
     def send_feedback(self, feedback: dict[str, float]) -> None:
         # TODO: Implement force feedback
         raise NotImplementedError
-
-    @check_if_not_connected
-    def disconnect(self) -> None:
-        self.left_arm.disconnect()
-        self.right_arm.disconnect()

src/lerobot/teleoperators/bi_openarm_leader/config_bi_openarm_leader.py

@@ -23,7 +23,7 @@ from ..openarm_leader import OpenArmLeaderConfigBase
 @TeleoperatorConfig.register_subclass("bi_openarm_leader")
 @dataclass
 class BiOpenArmLeaderConfig(TeleoperatorConfig):
-    """Configuration class for Bi OpenArm Follower robots."""
+    """Configuration class for Bi OpenArm Leader teleoperators."""
 
     left_arm_config: OpenArmLeaderConfigBase
     right_arm_config: OpenArmLeaderConfigBase

src/lerobot/teleoperators/bi_openarm_mini/__init__.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from .bi_openarm_mini import BiOpenArmMini
+from .config_bi_openarm_mini import BiOpenArmMiniConfig
+
+__all__ = ["BiOpenArmMini", "BiOpenArmMiniConfig"]

src/lerobot/teleoperators/bi_openarm_mini/bi_openarm_mini.py

@@ -0,0 +1,101 @@
+#!/usr/bin/env python
+
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+from functools import cached_property
+
+from lerobot.types import RobotAction
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
+
+from ..openarm_mini import OpenArmMini, OpenArmMiniConfig
+from ..teleoperator import Teleoperator
+from .config_bi_openarm_mini import BiOpenArmMiniConfig
+
+logger = logging.getLogger(__name__)
+
+
+class BiOpenArmMini(BimanualMixin, Teleoperator):
+    """Bimanual OpenArm Mini teleoperator.
+
+    Composes two single-arm :class:`OpenArmMini` instances. Action and feedback
+    keys of each arm are namespaced with a ``left_`` / ``right_`` prefix, so a
+    bimanual leader can teleoperate a bimanual OpenArm follower.
+    """
+
+    config_class = BiOpenArmMiniConfig
+    name = "bi_openarm_mini"
+
+    def __init__(self, config: BiOpenArmMiniConfig):
+        super().__init__(config)
+        self.config = config
+
+        # `side` is forced to match left/right regardless of what the user passed
+        # on the per-arm base config — the bimanual wrapper owns the side semantics.
+        left_arm_config = OpenArmMiniConfig(
+            id=f"{config.id}_left" if config.id else None,
+            calibration_dir=config.calibration_dir,
+            port=config.left_arm_config.port,
+            side="left",
+            use_degrees=config.left_arm_config.use_degrees,
+        )
+
+        right_arm_config = OpenArmMiniConfig(
+            id=f"{config.id}_right" if config.id else None,
+            calibration_dir=config.calibration_dir,
+            port=config.right_arm_config.port,
+            side="right",
+            use_degrees=config.right_arm_config.use_degrees,
+        )
+
+        self.left_arm = OpenArmMini(left_arm_config)
+        self.right_arm = OpenArmMini(right_arm_config)
+
+    @cached_property
+    def action_features(self) -> dict[str, type]:
+        return {
+            **{f"left_{k}": v for k, v in self.left_arm.action_features.items()},
+            **{f"right_{k}": v for k, v in self.right_arm.action_features.items()},
+        }
+
+    @cached_property
+    def feedback_features(self) -> dict[str, type]:
+        return {
+            **{f"left_{k}": v for k, v in self.left_arm.feedback_features.items()},
+            **{f"right_{k}": v for k, v in self.right_arm.feedback_features.items()},
+        }
+
+    def setup_motors(self) -> None:
+        self.left_arm.setup_motors()
+        self.right_arm.setup_motors()
+
+    @check_if_not_connected
+    def get_action(self) -> RobotAction:
+        action: RobotAction = {}
+        for k, v in self.left_arm.get_action().items():
+            action[f"left_{k}"] = v
+        for k, v in self.right_arm.get_action().items():
+            action[f"right_{k}"] = v
+        return action
+
+    @check_if_not_connected
+    def send_feedback(self, feedback: dict[str, float]) -> None:
+        left_fb = {k.removeprefix("left_"): v for k, v in feedback.items() if k.startswith("left_")}
+        right_fb = {k.removeprefix("right_"): v for k, v in feedback.items() if k.startswith("right_")}
+        if left_fb:
+            self.left_arm.send_feedback(left_fb)
+        if right_fb:
+            self.right_arm.send_feedback(right_fb)

src/lerobot/teleoperators/bi_openarm_mini/config_bi_openarm_mini.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from dataclasses import dataclass
+
+from ..config import TeleoperatorConfig
+from ..openarm_mini import OpenArmMiniConfigBase
+
+
+@TeleoperatorConfig.register_subclass("bi_openarm_mini")
+@dataclass
+class BiOpenArmMiniConfig(TeleoperatorConfig):
+    """Configuration class for Bi OpenArm Mini teleoperators."""
+
+    left_arm_config: OpenArmMiniConfigBase
+    right_arm_config: OpenArmMiniConfigBase

src/lerobot/teleoperators/bi_rebot_102_leader/__init__.py

@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .bi_rebot_102_leader import BiRebotArm102Leader
+from .bi_rebot_102_leader import BiRebot102Leader
-from .config_bi_rebot_102_leader import BiRebotArm102LeaderConfig
+from .config_bi_rebot_102_leader import BiRebot102LeaderConfig
 
-__all__ = ["BiRebotArm102Leader", "BiRebotArm102LeaderConfig"]
+__all__ = ["BiRebot102Leader", "BiRebot102LeaderConfig"]

src/lerobot/teleoperators/bi_rebot_102_leader/bi_rebot_102_leader.py

@@ -18,16 +18,17 @@ import logging
 from functools import cached_property
 
 from lerobot.types import RobotAction
-from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
 
 from ..rebot_102_leader import RebotArm102Leader, RebotArm102LeaderTeleopConfig
 from ..teleoperator import Teleoperator
-from .config_bi_rebot_102_leader import BiRebotArm102LeaderConfig
+from .config_bi_rebot_102_leader import BiRebot102LeaderConfig
 
 logger = logging.getLogger(__name__)
 
 
-class BiRebotArm102Leader(Teleoperator):
+class BiRebot102Leader(BimanualMixin, Teleoperator):
     """Bimanual Seeed Studio StarArm102 / reBot Arm 102 leader.
 
     Composes two single-arm :class:`RebotArm102Leader` instances. Action keys of
@@ -35,10 +36,10 @@ class BiRebotArm102Leader(Teleoperator):
     leader can teleoperate a bimanual reBot B601 follower.
     """
 
-    config_class = BiRebotArm102LeaderConfig
+    config_class = BiRebot102LeaderConfig
     name = "bi_rebot_102_leader"
 
-    def __init__(self, config: BiRebotArm102LeaderConfig):
+    def __init__(self, config: BiRebot102LeaderConfig):
         super().__init__(config)
         self.config = config
 
@@ -76,27 +77,6 @@ class BiRebotArm102Leader(Teleoperator):
     def feedback_features(self) -> dict[str, type]:
         return {}
 
-    @property
-    def is_connected(self) -> bool:
-        return self.left_arm.is_connected and self.right_arm.is_connected
-
-    @check_if_already_connected
-    def connect(self, calibrate: bool = True) -> None:
-        self.left_arm.connect(calibrate)
-        self.right_arm.connect(calibrate)
-
-    @property
-    def is_calibrated(self) -> bool:
-        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
-
-    def calibrate(self) -> None:
-        self.left_arm.calibrate()
-        self.right_arm.calibrate()
-
-    def configure(self) -> None:
-        self.left_arm.configure()
-        self.right_arm.configure()
-
     @check_if_not_connected
     def get_action(self) -> RobotAction:
         action_dict = {}
@@ -106,8 +86,3 @@ class BiRebotArm102Leader(Teleoperator):
 
     def send_feedback(self, feedback: dict[str, float]) -> None:
         raise NotImplementedError("Feedback is not implemented for the reBot Arm 102 leader.")
-
-    @check_if_not_connected
-    def disconnect(self) -> None:
-        self.left_arm.disconnect()
-        self.right_arm.disconnect()

src/lerobot/teleoperators/bi_rebot_102_leader/config_bi_rebot_102_leader.py

@@ -22,7 +22,7 @@ from ..rebot_102_leader import RebotArm102LeaderConfig
 
 @TeleoperatorConfig.register_subclass("bi_rebot_102_leader")
 @dataclass
-class BiRebotArm102LeaderConfig(TeleoperatorConfig):
+class BiRebot102LeaderConfig(TeleoperatorConfig):
     """Configuration class for the bimanual reBot Arm 102 leader teleoperator."""
 
     left_arm_config: RebotArm102LeaderConfig

src/lerobot/teleoperators/bi_so_leader/bi_so_leader.py

@@ -17,7 +17,9 @@
 import logging
 from functools import cached_property
 
-from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+from lerobot.types import RobotAction
+from lerobot.utils.bimanual import BimanualMixin
+from lerobot.utils.decorators import check_if_not_connected
 
 from ..so_leader import SOLeader, SOLeaderTeleopConfig
 from ..teleoperator import Teleoperator
@@ -26,7 +28,7 @@ from .config_bi_so_leader import BiSOLeaderConfig
 logger = logging.getLogger(__name__)
 
 
-class BiSOLeader(Teleoperator):
+class BiSOLeader(BimanualMixin, Teleoperator):
     """
     [Bimanual SO Leader Arms](https://github.com/TheRobotStudio/SO-ARM100) designed by TheRobotStudio
     """
@@ -67,33 +69,12 @@ class BiSOLeader(Teleoperator):
     def feedback_features(self) -> dict[str, type]:
         return {}
 
-    @property
-    def is_connected(self) -> bool:
-        return self.left_arm.is_connected and self.right_arm.is_connected
-
-    @check_if_already_connected
-    def connect(self, calibrate: bool = True) -> None:
-        self.left_arm.connect(calibrate)
-        self.right_arm.connect(calibrate)
-
-    @property
-    def is_calibrated(self) -> bool:
-        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
-
-    def calibrate(self) -> None:
-        self.left_arm.calibrate()
-        self.right_arm.calibrate()
-
-    def configure(self) -> None:
-        self.left_arm.configure()
-        self.right_arm.configure()
-
     def setup_motors(self) -> None:
         self.left_arm.setup_motors()
         self.right_arm.setup_motors()
 
     @check_if_not_connected
-    def get_action(self) -> dict[str, float]:
+    def get_action(self) -> RobotAction:
         action_dict = {}
 
         # Add "left_" prefix
@@ -109,8 +90,3 @@ class BiSOLeader(Teleoperator):
     def send_feedback(self, feedback: dict[str, float]) -> None:
         # TODO: Implement force feedback
         raise NotImplementedError
-
-    @check_if_not_connected
-    def disconnect(self) -> None:
-        self.left_arm.disconnect()
-        self.right_arm.disconnect()

src/lerobot/teleoperators/openarm_mini/__init__.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 
-# Copyright 2025 The HuggingFace Inc. team. All rights reserved.
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .config_openarm_mini import OpenArmMiniConfig
+from .config_openarm_mini import OpenArmMiniConfig, OpenArmMiniConfigBase
 from .openarm_mini import OpenArmMini
 
-__all__ = ["OpenArmMini", "OpenArmMiniConfig"]
+__all__ = ["OpenArmMini", "OpenArmMiniConfig", "OpenArmMiniConfigBase"]

src/lerobot/teleoperators/openarm_mini/config_openarm_mini.py

@@ -19,12 +19,21 @@ from dataclasses import dataclass
 from ..config import TeleoperatorConfig
 
 
-@TeleoperatorConfig.register_subclass("openarm_mini")
 @dataclass
-class OpenArmMiniConfig(TeleoperatorConfig):
+class OpenArmMiniConfigBase:
-    """Configuration for OpenArm Mini teleoperator with Feetech motors (dual arms)."""
+    """Base configuration for the OpenArm Mini teleoperator (Feetech STS3215, 7DOF + gripper)."""
 
-    port_right: str = "/dev/ttyUSB0"
+    # Serial port for the Feetech bus (e.g., "/dev/ttyUSB0").
-    port_left: str = "/dev/ttyUSB1"
+    port: str
+
+    # Side of the arm: "left" or "right". Controls per-joint direction flips applied
+    # during readout. If `None`, no flipping is applied.
+    side: str | None = None
 
     use_degrees: bool = True
+
+
+@TeleoperatorConfig.register_subclass("openarm_mini")
+@dataclass
+class OpenArmMiniConfig(TeleoperatorConfig, OpenArmMiniConfigBase):
+    pass

src/lerobot/teleoperators/openarm_mini/openarm_mini.py

@@ -31,22 +31,22 @@ from .config_openarm_mini import OpenArmMiniConfig
 
 logger = logging.getLogger(__name__)
 
-# Motors whose direction is inverted during readout
+# Per-side motor direction flips applied during readout.
-RIGHT_MOTORS_TO_FLIP = ["joint_1", "joint_2", "joint_3", "joint_4", "joint_5", "joint_7"]
+SIDE_MOTORS_TO_FLIP: dict[str, list[str]] = {
-LEFT_MOTORS_TO_FLIP = ["joint_1", "joint_3", "joint_4", "joint_5", "joint_6", "joint_7"]
+    "left": ["joint_1", "joint_3", "joint_4", "joint_5", "joint_6", "joint_7"],
+    "right": ["joint_1", "joint_2", "joint_3", "joint_4", "joint_5", "joint_7"],
+}
 
-# Leader joint 6 maps to follower joint 7 and vice versa
+# Leader joint 6 ↔ follower joint 7 (symmetric — its own inverse).
 JOINT_REMAP = {"joint_6": "joint_7", "joint_7": "joint_6"}
-JOINT_REMAP_REVERSE = {"joint_7": "joint_6", "joint_6": "joint_7"}
 
 GRIPPER_TELEOP_TO_DEGREES = -0.65
 
 
 class OpenArmMini(Teleoperator):
-    """
+    """OpenArm Mini single-arm teleoperator (Feetech STS3215, 7DOF + gripper).
-    OpenArm Mini Teleoperator with dual Feetech-based arms (8 motors per arm).
 
-    Each arm has 7 joints plus a gripper, using Feetech STS3215 servos.
+    For the bimanual setup, see :class:`BiOpenArmMini` which composes two of these.
     """
 
     config_class = OpenArmMiniConfig
@@ -56,9 +56,12 @@ class OpenArmMini(Teleoperator):
         super().__init__(config)
         self.config = config
 
+        if config.side is not None and config.side not in SIDE_MOTORS_TO_FLIP:
+            raise ValueError(f"Invalid side '{config.side}'; expected 'left', 'right', or None.")
+        self._motors_to_flip: list[str] = SIDE_MOTORS_TO_FLIP.get(config.side, []) if config.side else []
+
         norm_mode_body = MotorNormMode.DEGREES
-
+        motors = {
-        motors_right = {
             "joint_1": Motor(1, "sts3215", norm_mode_body),
             "joint_2": Motor(2, "sts3215", norm_mode_body),
             "joint_3": Motor(3, "sts3215", norm_mode_body),
@@ -69,46 +72,15 @@ class OpenArmMini(Teleoperator):
             "gripper": Motor(8, "sts3215", MotorNormMode.RANGE_0_100),
         }
 
-        motors_left = {
+        self.bus = FeetechMotorsBus(
-            "joint_1": Motor(1, "sts3215", norm_mode_body),
+            port=self.config.port,
-            "joint_2": Motor(2, "sts3215", norm_mode_body),
+            motors=motors,
-            "joint_3": Motor(3, "sts3215", norm_mode_body),
+            calibration=self.calibration,
-            "joint_4": Motor(4, "sts3215", norm_mode_body),
-            "joint_5": Motor(5, "sts3215", norm_mode_body),
-            "joint_6": Motor(6, "sts3215", norm_mode_body),
-            "joint_7": Motor(7, "sts3215", norm_mode_body),
-            "gripper": Motor(8, "sts3215", MotorNormMode.RANGE_0_100),
-        }
-
-        cal_right = {
-            k.replace("right_", ""): v for k, v in (self.calibration or {}).items() if k.startswith("right_")
-        }
-        cal_left = {
-            k.replace("left_", ""): v for k, v in (self.calibration or {}).items() if k.startswith("left_")
-        }
-
-        self.bus_right = FeetechMotorsBus(
-            port=self.config.port_right,
-            motors=motors_right,
-            calibration=cal_right,
-        )
-
-        self.bus_left = FeetechMotorsBus(
-            port=self.config.port_left,
-            motors=motors_left,
-            calibration=cal_left,
         )
 
     @property
     def action_features(self) -> dict[str, type]:
-        # Right first, then left — matches the robot (BiOpenArmFollower) ordering
+        return {f"{motor}.pos": float for motor in self.bus.motors}
-        # and the dataset feature names recorded during data collection.
-        features: dict[str, type] = {}
-        for motor in self.bus_right.motors:
-            features[f"right_{motor}.pos"] = float
-        for motor in self.bus_left.motors:
-            features[f"left_{motor}.pos"] = float
-        return features
 
     @property
     def feedback_features(self) -> dict[str, type]:
@@ -116,14 +88,12 @@ class OpenArmMini(Teleoperator):
 
     @property
     def is_connected(self) -> bool:
-        return self.bus_right.is_connected and self.bus_left.is_connected
+        return self.bus.is_connected
 
     @check_if_already_connected
     def connect(self, calibrate: bool = True) -> None:
-        logger.info(f"Connecting right arm on {self.config.port_right}...")
+        logger.info(f"Connecting arm on {self.config.port}...")
-        self.bus_right.connect()
+        self.bus.connect()
-        logger.info(f"Connecting left arm on {self.config.port_left}...")
-        self.bus_left.connect()
 
         if calibrate:
             self.calibrate()
@@ -133,14 +103,14 @@ class OpenArmMini(Teleoperator):
 
     @property
     def is_calibrated(self) -> bool:
-        return self.bus_right.is_calibrated and self.bus_left.is_calibrated
+        return self.bus.is_calibrated
 
     def calibrate(self) -> None:
         """
-        Run calibration procedure for OpenArm Mini.
+        Run calibration procedure for a single OpenArm Mini arm.
 
         1. Disable torque
-        2. Ask user to position arms in hanging position with grippers closed
+        2. Ask user to position arm in hanging position with gripper closed
         3. Set this as zero position via half-turn homing
         4. Interactive gripper calibration (open/close positions)
         5. Save calibration
@@ -152,70 +122,51 @@ class OpenArmMini(Teleoperator):
             )
             if user_input.strip().lower() != "c":
                 logger.info(f"Using existing calibration for {self.id}")
-                cal_right = {
+                self.bus.write_calibration(self.calibration)
-                    k.replace("right_", ""): v for k, v in self.calibration.items() if k.startswith("right_")
-                }
-                cal_left = {
-                    k.replace("left_", ""): v for k, v in self.calibration.items() if k.startswith("left_")
-                }
-                self.bus_right.write_calibration(cal_right)
-                self.bus_left.write_calibration(cal_left)
                 return
 
         logger.info(f"\nRunning calibration for {self}")
 
-        self._calibrate_arm("right", self.bus_right)
+        self.bus.disable_torque()
-        self._calibrate_arm("left", self.bus_left)
 
-        self._save_calibration()
+        logger.info("Setting Phase to 12 for all motors...")
-        print(f"\nCalibration complete and saved to {self.calibration_fpath}")
+        for motor in self.bus.motors:
+            self.bus.write("Phase", motor, 12)
 
-    def _calibrate_arm(self, arm_name: str, bus: FeetechMotorsBus) -> None:
+        for motor in self.bus.motors:
-        """Calibrate a single arm with Feetech motors."""
+            self.bus.write("Operating_Mode", motor, OperatingMode.POSITION.value)
-        logger.info(f"\n=== Calibrating {arm_name.upper()} arm ===")
-
-        bus.disable_torque()
-
-        logger.info(f"Setting Phase to 12 for all motors in {arm_name.upper()} arm...")
-        for motor in bus.motors:
-            bus.write("Phase", motor, 12)
-
-        for motor in bus.motors:
-            bus.write("Operating_Mode", motor, OperatingMode.POSITION.value)
 
         input(
-            f"\nCalibration: Zero Position ({arm_name.upper()} arm)\n"
+            "\nCalibration: Zero Position\n"
             "Position the arm in the following configuration:\n"
             "  - Arm hanging straight down\n"
             "  - Gripper closed\n"
             "Press ENTER when ready..."
         )
 
-        homing_offsets = bus.set_half_turn_homings()
+        homing_offsets = self.bus.set_half_turn_homings()
-        logger.info(f"{arm_name.capitalize()} arm zero position set.")
+        logger.info("Arm zero position set.")
 
-        print(f"\nSetting motor ranges for {arm_name.upper()} arm\n")
+        print("\nSetting motor ranges\n")
 
         if self.calibration is None:
             self.calibration = {}
 
-        motor_resolution = bus.model_resolution_table[list(bus.motors.values())[0].model]
+        motor_resolution = self.bus.model_resolution_table[list(self.bus.motors.values())[0].model]
         max_res = motor_resolution - 1
 
-        for motor_name, motor in bus.motors.items():
+        for motor_name, motor in self.bus.motors.items():
-            prefixed_name = f"{arm_name}_{motor_name}"
-
             if motor_name == "gripper":
                 input(
-                    f"\nGripper Calibration ({arm_name.upper()} arm)\n"
+                    "\nGripper Calibration\n"
-                    f"Step 1: CLOSE the gripper fully\n"
+                    "Step 1: CLOSE the gripper fully\n"
-                    f"Press ENTER when gripper is closed..."
+                    "Press ENTER when gripper is closed..."
                 )
-                closed_pos = bus.read("Present_Position", motor_name, normalize=False)
+                closed_pos = self.bus.read("Present_Position", motor_name, normalize=False)
                 logger.info(f"  Gripper closed position recorded: {closed_pos}")
 
                 input("\nStep 2: OPEN the gripper fully\nPress ENTER when gripper is fully open...")
-                open_pos = bus.read("Present_Position", motor_name, normalize=False)
+                open_pos = self.bus.read("Present_Position", motor_name, normalize=False)
                 logger.info(f"  Gripper open position recorded: {open_pos}")
 
                 if closed_pos < open_pos:
@@ -228,16 +179,16 @@ class OpenArmMini(Teleoperator):
                     drive_mode = 1
 
                 logger.info(
-                    f"  {prefixed_name}: range set to [{range_min}, {range_max}] "
+                    f"  {motor_name}: range set to [{range_min}, {range_max}] "
                     f"(0=closed, 100=open, drive_mode={drive_mode})"
                 )
             else:
                 range_min = 0
                 range_max = max_res
                 drive_mode = 0
-                logger.info(f"  {prefixed_name}: range set to [0, {max_res}] (full motor range)")
+                logger.info(f"  {motor_name}: range set to [0, {max_res}] (full motor range)")
 
-            self.calibration[prefixed_name] = MotorCalibration(
+            self.calibration[motor_name] = MotorCalibration(
                 id=motor.id,
                 drive_mode=drive_mode,
                 homing_offset=homing_offsets[motor_name],
@@ -245,108 +196,68 @@ class OpenArmMini(Teleoperator):
                 range_max=range_max,
             )
 
-        cal_for_bus = {
+        self.bus.write_calibration(self.calibration)
-            k.replace(f"{arm_name}_", ""): v
+        self._save_calibration()
-            for k, v in self.calibration.items()
+        print(f"\nCalibration complete and saved to {self.calibration_fpath}")
-            if k.startswith(f"{arm_name}_")
-        }
-        bus.write_calibration(cal_for_bus)
 
     def configure(self) -> None:
-        self.bus_right.disable_torque()
+        self.bus.disable_torque()
-        self.bus_right.configure_motors()
+        self.bus.configure_motors()
-        for motor in self.bus_right.motors:
+        for motor in self.bus.motors:
-            self.bus_right.write("Operating_Mode", motor, OperatingMode.POSITION.value)
+            self.bus.write("Operating_Mode", motor, OperatingMode.POSITION.value)
-
-        self.bus_left.disable_torque()
-        self.bus_left.configure_motors()
-        for motor in self.bus_left.motors:
-            self.bus_left.write("Operating_Mode", motor, OperatingMode.POSITION.value)
 
     def setup_motors(self) -> None:
-        print("\nSetting up RIGHT arm motors...")
+        for motor in reversed(self.bus.motors):
-        for motor in reversed(self.bus_right.motors):
+            input(f"Connect the controller board to the '{motor}' motor only and press enter.")
-            input(f"Connect the controller board to the RIGHT '{motor}' motor only and press enter.")
+            self.bus.setup_motor(motor)
-            self.bus_right.setup_motor(motor)
+            print(f"'{motor}' motor id set to {self.bus.motors[motor].id}")
-            print(f"RIGHT '{motor}' motor id set to {self.bus_right.motors[motor].id}")
-
-        print("\nSetting up LEFT arm motors...")
-        for motor in reversed(self.bus_left.motors):
-            input(f"Connect the controller board to the LEFT '{motor}' motor only and press enter.")
-            self.bus_left.setup_motor(motor)
-            print(f"LEFT '{motor}' motor id set to {self.bus_left.motors[motor].id}")
 
     @check_if_not_connected
     def get_action(self) -> RobotAction:
-        """Get current action from both arms (read positions from all motors)."""
+        """Get current action (read positions from all motors)."""
         start = time.perf_counter()
 
-        right_positions = self.bus_right.sync_read("Present_Position")
+        positions = self.bus.sync_read("Present_Position")
-        left_positions = self.bus_left.sync_read("Present_Position")
 
-        # Right first, then left — matches the robot (BiOpenArmFollower) ordering
-        # and the dataset feature names recorded during data collection.
         # Joint 6↔7 remap: leader joint_6 → follower joint_7 and vice versa.
+        # Per-side direction flip is applied based on the configured `side`.
         action: dict[str, Any] = {}
-        for motor, val in right_positions.items():
+        for motor, val in positions.items():
             target = JOINT_REMAP.get(motor, motor)
             if motor == "gripper":
                 # Convert gripper from teleop 0-100 to openarms degrees: 0→0°, 100→-65°
-                action[f"right_{target}.pos"] = val * GRIPPER_TELEOP_TO_DEGREES
+                action[f"{target}.pos"] = val * GRIPPER_TELEOP_TO_DEGREES
             else:
-                action[f"right_{target}.pos"] = -val if motor in RIGHT_MOTORS_TO_FLIP else val
+                action[f"{target}.pos"] = -val if motor in self._motors_to_flip else val
-        for motor, val in left_positions.items():
-            target = JOINT_REMAP.get(motor, motor)
-            if motor == "gripper":
-                action[f"left_{target}.pos"] = val * GRIPPER_TELEOP_TO_DEGREES
-            else:
-                action[f"left_{target}.pos"] = -val if motor in LEFT_MOTORS_TO_FLIP else val
 
         dt_ms = (time.perf_counter() - start) * 1e3
         logger.debug(f"{self} read action: {dt_ms:.1f}ms")
         return action
 
     def enable_torque(self) -> None:
-        """Enable torque on both arms for position control."""
+        self.bus.enable_torque()
-        self.bus_right.enable_torque()
-        self.bus_left.enable_torque()
 
     def disable_torque(self) -> None:
-        """Disable torque on both arms for free movement."""
+        self.bus.disable_torque()
-        self.bus_right.disable_torque()
-        self.bus_left.disable_torque()
 
     def write_goal_positions(self, positions: dict[str, float]) -> None:
         """Write goal positions to motors (inverse of get_action flip/gripper/remap logic)."""
-        right_goals: dict[str, float] = {}
+        goals: dict[str, float] = {}
-        left_goals: dict[str, float] = {}
-
         for key, val in positions.items():
             if not key.endswith(".pos"):
                 continue
-            motor_name = key.removesuffix(".pos")
+            base = key.removesuffix(".pos")
-            if motor_name.startswith("right_"):
+            # JOINT_REMAP is symmetric (its own inverse).
-                base = motor_name.removeprefix("right_")
+            target = JOINT_REMAP.get(base, base)
-                # Reverse remap: follower joint_7 → leader joint_6 and vice versa
+            if base == "gripper":
-                target = JOINT_REMAP_REVERSE.get(base, base)
+                # Convert robot degrees to teleop 0-100: 0°→0, -65°→100
-                if base == "gripper":
+                goals[target] = val / GRIPPER_TELEOP_TO_DEGREES
-                    # Convert robot degrees to teleop 0-100: 0°→0, -65°→100
+            else:
-                    right_goals[target] = val / GRIPPER_TELEOP_TO_DEGREES
+                # Un-flip using the ORIGINAL motor name (target = leader motor)
-                else:
+                goals[target] = -val if target in self._motors_to_flip else val
-                    # Un-flip using the ORIGINAL motor name (target = leader motor)
-                    right_goals[target] = -val if target in RIGHT_MOTORS_TO_FLIP else val
-            elif motor_name.startswith("left_"):
-                base = motor_name.removeprefix("left_")
-                target = JOINT_REMAP_REVERSE.get(base, base)
-                if base == "gripper":
-                    left_goals[target] = val / GRIPPER_TELEOP_TO_DEGREES
-                else:
-                    left_goals[target] = -val if target in LEFT_MOTORS_TO_FLIP else val
 
-        if right_goals:
+        if goals:
-            self.bus_right.sync_write("Goal_Position", right_goals)
+            self.bus.sync_write("Goal_Position", goals)
-        if left_goals:
-            self.bus_left.sync_write("Goal_Position", left_goals)
 
     @check_if_not_connected
     def send_feedback(self, feedback: dict[str, float]) -> None:
@@ -354,6 +265,5 @@ class OpenArmMini(Teleoperator):
 
     @check_if_not_connected
     def disconnect(self) -> None:
-        self.bus_right.disconnect()
+        self.bus.disconnect()
-        self.bus_left.disconnect()
         logger.info(f"{self} disconnected.")

src/lerobot/teleoperators/utils.py

@@ -99,14 +99,18 @@ def make_teleoperator_from_config(config: TeleoperatorConfig) -> "Teleoperator":
         from .openarm_mini import OpenArmMini
 
         return OpenArmMini(config)
+    elif config.type == "bi_openarm_mini":
+        from .bi_openarm_mini import BiOpenArmMini
+
+        return BiOpenArmMini(config)
     elif config.type == "rebot_102_leader":
         from .rebot_102_leader import RebotArm102Leader
 
         return RebotArm102Leader(config)
     elif config.type == "bi_rebot_102_leader":
-        from .bi_rebot_102_leader import BiRebotArm102Leader
+        from .bi_rebot_102_leader import BiRebot102Leader
 
-        return BiRebotArm102Leader(config)
+        return BiRebot102Leader(config)
     else:
         try:
             return cast("Teleoperator", make_device_from_device_class(config))

src/lerobot/utils/bimanual.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python
+
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import Any
+
+from lerobot.utils.decorators import check_if_already_connected, check_if_not_connected
+
+
+class BimanualMixin:
+    """Lifecycle delegation for bimanual robots and teleoperators.
+
+    Concrete subclasses must populate ``self.left_arm`` and ``self.right_arm`` in
+    their own ``__init__``. They retain ownership of feature dicts and the
+    data-routing methods (``get_action`` / ``send_action`` / ``get_observation`` /
+    ``send_feedback``), which vary per-embodiment.
+
+    Inherit before the ``Robot`` / ``Teleoperator`` base so the mixin's methods
+    take precedence in the MRO::
+
+        class BiFooFollower(BimanualMixin, Robot): ...
+    """
+
+    left_arm: Any
+    right_arm: Any
+
+    @property
+    def is_connected(self) -> bool:
+        return self.left_arm.is_connected and self.right_arm.is_connected
+
+    @property
+    def is_calibrated(self) -> bool:
+        return self.left_arm.is_calibrated and self.right_arm.is_calibrated
+
+    @check_if_already_connected
+    def connect(self, calibrate: bool = True) -> None:
+        self.left_arm.connect(calibrate)
+        self.right_arm.connect(calibrate)
+
+    def calibrate(self) -> None:
+        self.left_arm.calibrate()
+        self.right_arm.calibrate()
+
+    def configure(self) -> None:
+        self.left_arm.configure()
+        self.right_arm.configure()
+
+    @check_if_not_connected
+    def disconnect(self) -> None:
+        self.left_arm.disconnect()
+        self.right_arm.disconnect()

src/lerobot/utils/import_utils.py

@@ -216,9 +216,15 @@ def register_third_party_plugins() -> None:
 
     This function uses `importlib.metadata` to find packages installed in the environment
     (including editable installs) starting with 'lerobot_robot_', 'lerobot_camera_',
-    'lerobot_teleoperator_', or 'lerobot_policy_' and imports them.
+    'lerobot_teleoperator_', 'lerobot_policy_', or 'lerobot_env_' and imports them.
     """
-    prefixes = ("lerobot_robot_", "lerobot_camera_", "lerobot_teleoperator_", "lerobot_policy_")
+    prefixes = (
+        "lerobot_robot_",
+        "lerobot_camera_",
+        "lerobot_teleoperator_",
+        "lerobot_policy_",
+        "lerobot_env_",
+    )
     imported: list[str] = []
     failed: list[str] = []
 

tests/annotations/test_writer.py

@@ -28,6 +28,7 @@ import pytest
 pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
 pytest.importorskip("pandas", reason="pandas is required (install lerobot[dataset])")
 
+import pandas as pd  # noqa: E402
 import pyarrow.parquet as pq  # noqa: E402
 
 from lerobot.annotations.steerable_pipeline.reader import iter_episodes  # noqa: E402
@@ -344,6 +345,78 @@ def test_annotation_metadata_sync_allows_non_streaming_load(
     assert len(dataset) == 24
 
 
+def _build_packed_dataset(root: Path, episode_lengths: list[int], *, fps: int = 10) -> Path:
+    """Pack several episodes into a single shard (vs build_annotation_dataset's one-per-file),
+    so the writer's rewrite must re-emit one row group per episode instead of collapsing them."""
+    from lerobot.datasets.io_utils import write_tasks
+    from lerobot.utils.io_utils import write_json
+
+    data_dir = root / "data" / "chunk-000"
+    data_dir.mkdir(parents=True, exist_ok=True)
+
+    episode_index, frame_index, timestamp, task_index, subtask_index = [], [], [], [], []
+    for ep, length in enumerate(episode_lengths):
+        episode_index += [ep] * length
+        frame_index += list(range(length))
+        timestamp += [round(i / fps, 6) for i in range(length)]
+        task_index += [0] * length
+        subtask_index += [0] * length  # legacy column the writer must drop
+    pd.DataFrame(
+        {
+            "episode_index": episode_index,
+            "frame_index": frame_index,
+            "timestamp": timestamp,
+            "task_index": task_index,
+            "subtask_index": subtask_index,
+        }
+    ).to_parquet(data_dir / "file-000.parquet", index=False)
+
+    tasks_df = pd.DataFrame({"task_index": [0]}, index=pd.Index(["do the thing"], name="task"))
+    write_tasks(tasks_df, root)
+    write_json(
+        {"codebase_version": "v3.1", "fps": fps, "features": {}, "total_episodes": len(episode_lengths)},
+        root / "meta" / "info.json",
+    )
+    return root
+
+
+def test_writer_one_row_group_per_episode(tmp_path: Path) -> None:
+    """Rewriting a packed shard must keep one row group per episode, not collapse
+    every episode into a single giant row group."""
+    episode_lengths = [4, 6, 5]  # unequal lengths, all in one shard
+    root = _build_packed_dataset(tmp_path / "ds", episode_lengths)
+    shard = root / "data" / "chunk-000" / "file-000.parquet"
+    assert pq.ParquetFile(shard).metadata.num_row_groups == 1, "fixture should start collapsed"
+
+    staging_dir = tmp_path / "stage"
+    for ep in range(len(episode_lengths)):
+        _stage_episode(
+            staging_dir,
+            ep,
+            plan=[
+                {
+                    "role": "assistant",
+                    "content": f"subtask for ep {ep}",
+                    "style": "subtask",
+                    "timestamp": 0.0,
+                    "tool_calls": None,
+                }
+            ],
+        )
+
+    records = list(iter_episodes(root))
+    LanguageColumnsWriter().write_all(records, staging_dir, root)
+
+    # One row group per episode, with row counts matching the episode lengths.
+    md = pq.ParquetFile(shard).metadata
+    assert md.num_row_groups == len(episode_lengths)
+    assert [md.row_group(i).num_rows for i in range(md.num_row_groups)] == episode_lengths
+    # Language columns are still present after the per-episode rewrite.
+    table = pq.read_table(shard)
+    assert "language_persistent" in table.column_names
+    assert "language_events" in table.column_names
+
+
 def test_speech_atom_shape_matches_plan_spec() -> None:
     atom = speech_atom(2.5, "I'm cleaning up!")
     assert atom["role"] == "assistant"

tests/datasets/test_aggregate.py

@@ -32,6 +32,26 @@ from lerobot.datasets.lerobot_dataset import LeRobotDataset
 from tests.fixtures.constants import DUMMY_REPO_ID
 
 
+def assert_data_shards_one_row_group_per_episode(root):
+    """Every aggregated DATA shard must have exactly one parquet row group per episode."""
+    import pyarrow.parquet as pq
+
+    shards = sorted((root / "data").rglob("*.parquet"))
+    assert shards, f"no data shards found under {root}/data"
+    n_episodes = 0
+    for shard in shards:
+        pf = pq.ParquetFile(shard)
+        episodes = pf.read(columns=["episode_index"]).column("episode_index").to_pylist()
+        assert pf.metadata.num_row_groups == len(set(episodes)), shard
+        for i in range(pf.metadata.num_row_groups):
+            rg_episodes = set(
+                pf.read_row_group(i, columns=["episode_index"]).column("episode_index").to_pylist()
+            )
+            assert len(rg_episodes) == 1, f"{shard} row group {i} spans episodes {rg_episodes}"
+        n_episodes += len(set(episodes))
+    return n_episodes
+
+
 def assert_episode_and_frame_counts(aggr_ds, expected_episodes, expected_frames):
     """Test that total number of episodes and frames are correctly aggregated."""
     assert aggr_ds.num_episodes == expected_episodes, (
@@ -566,6 +586,41 @@ def assert_image_frames_integrity(aggr_ds, ds_0, ds_1):
             )
 
 
+@pytest.mark.parametrize("use_videos", [True, False], ids=["video", "image"])
+def test_aggregate_one_row_group_per_episode(tmp_path, lerobot_dataset_factory, use_videos):
+    """Aggregated DATA shards keep one row group per episode (not one collapsed group).
+
+    Covers both the non-image (``df.to_parquet``) and image
+    (``to_parquet_with_hf_images``) write branches, including the merge-into-
+    existing-file branch via a low file-size threshold that forces packing.
+    """
+    ds_0 = lerobot_dataset_factory(
+        root=tmp_path / "rg_0",
+        repo_id=f"{DUMMY_REPO_ID}_rg_0",
+        total_episodes=3,
+        total_frames=60,
+        use_videos=use_videos,
+    )
+    ds_1 = lerobot_dataset_factory(
+        root=tmp_path / "rg_1",
+        repo_id=f"{DUMMY_REPO_ID}_rg_1",
+        total_episodes=4,
+        total_frames=80,
+        use_videos=use_videos,
+    )
+
+    aggr_root = tmp_path / "rg_aggr"
+    aggregate_datasets(
+        repo_ids=[ds_0.repo_id, ds_1.repo_id],
+        roots=[ds_0.root, ds_1.root],
+        aggr_repo_id=f"{DUMMY_REPO_ID}_rg_aggr",
+        aggr_root=aggr_root,
+    )
+
+    n_episodes = assert_data_shards_one_row_group_per_episode(aggr_root)
+    assert n_episodes == ds_0.num_episodes + ds_1.num_episodes
+
+
 def test_aggregate_image_datasets(tmp_path, lerobot_dataset_factory):
     """Test aggregation of image-based datasets preserves HuggingFace Image schema.
 

tests/datasets/test_datasets.py

@@ -51,7 +51,7 @@ from lerobot.robots import make_robot_from_config
 from lerobot.transforms import ImageTransforms, ImageTransformsConfig
 from lerobot.utils.constants import ACTION, DONE, OBS_IMAGES, OBS_STATE, OBS_STR, REWARD
 from lerobot.utils.feature_utils import hw_to_dataset_features
-from tests.fixtures.constants import DUMMY_CHW, DUMMY_HWC, DUMMY_REPO_ID
+from tests.fixtures.constants import DUMMY_CHW, DUMMY_HWC, DUMMY_MOTOR_FEATURES, DUMMY_REPO_ID
 from tests.mocks.mock_robot import MockRobotConfig
 from tests.utils import require_x86_64_kernel
 
@@ -133,6 +133,21 @@ def test_dataset_feature_with_forward_slash_raises_error():
         )
 
 
+def test_create_does_not_mutate_input_features(tmp_path, empty_lerobot_dataset_factory):
+    # ``create`` must deep-copy features so a dataset built from another's features stays independent.
+    dataset = empty_lerobot_dataset_factory(
+        root=tmp_path / "ds1", features=DUMMY_MOTOR_FEATURES, use_videos=False
+    )
+    dataset_copy = empty_lerobot_dataset_factory(
+        root=tmp_path / "ds2", features=dataset.meta.features, use_videos=False
+    )
+
+    original_shape = dataset.meta.info.features["state"]["shape"]
+    dataset_copy.meta.info.features["state"]["shape"] = (999,)
+
+    assert dataset.meta.info.features["state"]["shape"] == original_shape
+
+
 def test_add_frame_missing_task(tmp_path, empty_lerobot_dataset_factory):
     features = {"state": {"dtype": "float32", "shape": (1,), "names": None}}
     dataset = empty_lerobot_dataset_factory(root=tmp_path / "test", features=features)

tests/optim/test_optimizers.py

@@ -20,6 +20,7 @@ from lerobot.optim.optimizers import (
     MultiAdamConfig,
     SGDConfig,
     load_optimizer_state,
+    load_optimizer_state_dict,
     save_optimizer_state,
 )
 from lerobot.utils.constants import (
@@ -65,6 +66,44 @@ def test_save_and_load_optimizer_state(model_params, optimizer, tmp_path):
     torch.testing.assert_close(optimizer.state_dict(), loaded_optimizer.state_dict())
 
 
+def test_save_and_load_fsdp_optimizer_state_dict_roundtrip(tmp_path):
+    """The FSDP full optimizer state dict is keyed by parameter FQNs (dotted strings), not the
+    integer indices of the single-GPU path. Verify it survives the safetensors save -> read
+    round-trip used by the FSDP save/resume path (save_optimizer_state(optim_state_dict=...) then
+    load_optimizer_state_dict), which the flatten/unflatten "/" separator must not corrupt."""
+    full_osd = {
+        "state": {
+            "model.layers.0.weight": {
+                "step": torch.tensor(3.0),
+                "exp_avg": torch.randn(4, 4),
+                "exp_avg_sq": torch.randn(4, 4),
+            },
+            "model.layers.0.bias": {
+                "step": torch.tensor(3.0),
+                "exp_avg": torch.randn(4),
+                "exp_avg_sq": torch.randn(4),
+            },
+        },
+        "param_groups": [
+            {"lr": 1e-4, "betas": [0.9, 0.999], "eps": 1e-8, "weight_decay": 0.0, "params": [0, 1]}
+        ],
+    }
+
+    save_optimizer_state(
+        torch.optim.Adam([torch.nn.Parameter(torch.randn(1))]), tmp_path, optim_state_dict=full_osd
+    )
+    assert (tmp_path / OPTIMIZER_STATE).is_file()
+    assert (tmp_path / OPTIMIZER_PARAM_GROUPS).is_file()
+
+    loaded = load_optimizer_state_dict(tmp_path)
+    # FQN keys must be preserved verbatim (not int-cast, not split on their dots).
+    assert set(loaded["state"].keys()) == set(full_osd["state"].keys())
+    for fqn, sub in full_osd["state"].items():
+        for k, v in sub.items():
+            torch.testing.assert_close(loaded["state"][fqn][k], v)
+    assert loaded["param_groups"] == full_osd["param_groups"]
+
+
 @pytest.fixture
 def base_params_dict():
     return {

tests/policies/test_policies.py

@@ -23,6 +23,7 @@ import torch
 
 pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
 
+from huggingface_hub.constants import SAFETENSORS_SINGLE_FILE
 from packaging import version
 from safetensors.torch import load_file
 
@@ -300,6 +301,29 @@ def test_save_and_load_pretrained(dummy_dataset_metadata, tmp_path, policy_name:
     torch.testing.assert_close(list(policy.parameters()), list(loaded_policy.parameters()), rtol=0, atol=0)
 
 
+def test_save_pretrained_with_state_dict(dummy_dataset_metadata, tmp_path):
+    """Exercise the FSDP checkpoint path: save_pretrained with a pre-gathered state_dict."""
+    policy_cls = get_policy_class("act")
+    policy_cfg = make_policy_config("act")
+    features = dataset_to_policy_features(dummy_dataset_metadata.features)
+    policy_cfg.output_features = {key: ft for key, ft in features.items() if ft.type is FeatureType.ACTION}
+    policy_cfg.input_features = {
+        key: ft for key, ft in features.items() if key not in policy_cfg.output_features
+    }
+    policy = policy_cls(policy_cfg)
+    policy.to(policy_cfg.device)
+
+    save_dir = tmp_path / "fsdp_state_dict"
+    policy.save_pretrained(save_dir, state_dict=policy.state_dict())
+
+    # A single, unsharded safetensors file (no sharded set + index).
+    assert (save_dir / SAFETENSORS_SINGLE_FILE).is_file()
+    assert not (save_dir / f"{SAFETENSORS_SINGLE_FILE}.index.json").exists()
+
+    loaded_policy = policy_cls.from_pretrained(save_dir, config=policy_cfg)
+    torch.testing.assert_close(list(policy.parameters()), list(loaded_policy.parameters()), rtol=0, atol=0)
+
+
 @pytest.mark.parametrize("multikey", [True, False])
 def test_multikey_construction(multikey: bool):
     """

tests/processor/test_pipeline.py

@@ -2370,14 +2370,32 @@ def test_aggregate_images_when_use_videos_false():
     out = aggregate_pipeline_dataset_features(
         pipeline=rp,
         initial_features={PipelineFeatureType.ACTION: {}, PipelineFeatureType.OBSERVATION: initial},
-        use_videos=False,  # expect "image" dtype
+        use_videos=False,  # images kept, stored as "image" dtype
         patterns=None,
     )
 
     key = f"{OBS_IMAGES}.back"
     key_front = f"{OBS_IMAGES}.front"
-    assert key not in out
+    assert key in out
-    assert key_front not in out
+    assert key_front in out
+    assert out[key]["dtype"] == "image"
+    assert out[key_front]["dtype"] == "image"
+    assert out[key]["shape"] == initial["back"]
+
+
+def test_aggregate_images_excluded():
+    rp = DataProcessorPipeline([AddObservationStateFeatures(add_front_image=True)])
+    initial = {"back": (480, 640, 3)}
+
+    out = aggregate_pipeline_dataset_features(
+        pipeline=rp,
+        initial_features={PipelineFeatureType.ACTION: {}, PipelineFeatureType.OBSERVATION: initial},
+        exclude_images=True,
+        patterns=None,
+    )
+
+    assert f"{OBS_IMAGES}.back" not in out
+    assert f"{OBS_IMAGES}.front" not in out
 
 
 def test_aggregate_images_when_use_videos_true():

tests/teleoperators/test_rebot_102_leader.py

@@ -18,7 +18,7 @@ from unittest.mock import MagicMock, patch
 
 import pytest
 
-from lerobot.teleoperators.bi_rebot_102_leader import BiRebotArm102Leader, BiRebotArm102LeaderConfig
+from lerobot.teleoperators.bi_rebot_102_leader import BiRebot102Leader, BiRebot102LeaderConfig
 from lerobot.teleoperators.rebot_102_leader import (
     RebotArm102Leader,
     RebotArm102LeaderConfig,
@@ -91,11 +91,11 @@ def test_send_feedback_not_implemented(leader):
 
 def test_bimanual_prefixes_features():
     with patch(f"{_MODULE}.require_package", lambda *a, **kw: None):
-        cfg = BiRebotArm102LeaderConfig(
+        cfg = BiRebot102LeaderConfig(
             left_arm_config=RebotArm102LeaderConfig(port="/dev/null0"),
             right_arm_config=RebotArm102LeaderConfig(port="/dev/null1"),
         )
-        teleop = BiRebotArm102Leader(cfg)
+        teleop = BiRebot102Leader(cfg)
     assert any(k.startswith("left_") for k in teleop.action_features)
     assert any(k.startswith("right_") for k in teleop.action_features)
     assert "left_gripper.pos" in teleop.action_features

tests/training/test_multi_gpu.py

@@ -58,7 +58,46 @@ def download_dataset(repo_id, episodes):
     print(f"Dataset {repo_id} downloaded successfully")
 
 
-def run_accelerate_training(config_args, num_processes=4, temp_dir=None):
+def _write_multi_gpu_config(f, num_processes):
+    f.write("compute_environment: LOCAL_MACHINE\n")
+    f.write("distributed_type: MULTI_GPU\n")
+    f.write("mixed_precision: 'no'\n")
+    f.write(f"num_processes: {num_processes}\n")
+    f.write("use_cpu: false\n")
+    f.write("gpu_ids: all\n")
+    f.write("downcast_bf16: 'no'\n")
+    f.write("machine_rank: 0\n")
+    f.write("main_training_function: main\n")
+    f.write("num_machines: 1\n")
+    f.write("rdzv_backend: static\n")
+    f.write("same_network: true\n")
+
+
+def _write_fsdp_config(f, num_processes):
+    # FSDP1 with FULL_SHARD (ZeRO-3-equivalent) and FULL_STATE_DICT, matching
+    # docs/source/multi_gpu_training.mdx. ACT's repeated transformer blocks are the wrap units;
+    # fsdp_use_orig_params is required because LeRobot builds the optimizer before prepare().
+    f.write("compute_environment: LOCAL_MACHINE\n")
+    f.write("distributed_type: FSDP\n")
+    f.write("mixed_precision: 'no'\n")
+    f.write(f"num_processes: {num_processes}\n")
+    f.write("use_cpu: false\n")
+    f.write("gpu_ids: all\n")
+    f.write("machine_rank: 0\n")
+    f.write("main_training_function: main\n")
+    f.write("num_machines: 1\n")
+    f.write("rdzv_backend: static\n")
+    f.write("same_network: true\n")
+    f.write("fsdp_config:\n")
+    f.write("  fsdp_version: 1\n")
+    f.write("  fsdp_sharding_strategy: FULL_SHARD\n")
+    f.write("  fsdp_auto_wrap_policy: TRANSFORMER_BASED_WRAP\n")
+    f.write("  fsdp_transformer_layer_cls_to_wrap: ACTEncoderLayer,ACTDecoderLayer\n")
+    f.write("  fsdp_use_orig_params: true\n")
+    f.write("  fsdp_state_dict_type: FULL_STATE_DICT\n")
+
+
+def run_accelerate_training(config_args, num_processes=4, temp_dir=None, distributed_type="MULTI_GPU"):
     """
     Helper function to run training with accelerate launch.
 
@@ -66,6 +105,7 @@ def run_accelerate_training(config_args, num_processes=4, temp_dir=None):
         config_args: List of config arguments to pass to lerobot_train.py
         num_processes: Number of processes (GPUs) to use
         temp_dir: Temporary directory for outputs
+        distributed_type: "MULTI_GPU" (DDP) or "FSDP" — selects the generated accelerate config.
 
     Returns:
         subprocess.CompletedProcess result
@@ -75,18 +115,10 @@ def run_accelerate_training(config_args, num_processes=4, temp_dir=None):
 
     # Write YAML config
     with open(config_path, "w") as f:
-        f.write("compute_environment: LOCAL_MACHINE\n")
+        if distributed_type == "FSDP":
-        f.write("distributed_type: MULTI_GPU\n")
+            _write_fsdp_config(f, num_processes)
-        f.write("mixed_precision: 'no'\n")
+        else:
-        f.write(f"num_processes: {num_processes}\n")
+            _write_multi_gpu_config(f, num_processes)
-        f.write("use_cpu: false\n")
-        f.write("gpu_ids: all\n")
-        f.write("downcast_bf16: 'no'\n")
-        f.write("machine_rank: 0\n")
-        f.write("main_training_function: main\n")
-        f.write("num_machines: 1\n")
-        f.write("rdzv_backend: static\n")
-        f.write("same_network: true\n")
 
     cmd = [
         "accelerate",
@@ -211,3 +243,66 @@ class TestMultiGPUTraining:
                 # Verify optimizer state exists
                 optimizer_state = training_state_dir / "optimizer_state.safetensors"
                 assert optimizer_state.exists(), f"No optimizer state in checkpoint {checkpoint_dir}"
+
+    def test_fsdp_optimizer_save_and_resume(self):
+        """
+        Test that FSDP saves the (gathered) optimizer state and can resume from it.
+
+        Trains a few steps under FSDP, verifies the gathered optimizer state is written next to the
+        rest of the training state, then resumes from the checkpoint for more steps and checks it
+        completes without shape/key errors in the FSDP optimizer load path.
+        """
+        # Pre-download dataset to avoid race conditions
+        download_dataset("lerobot/pusht", episodes=[0])
+
+        with tempfile.TemporaryDirectory() as temp_dir:
+            output_dir = Path(temp_dir) / "outputs"
+
+            config_args = [
+                "--dataset.repo_id=lerobot/pusht",
+                "--dataset.episodes=[0]",
+                "--policy.type=act",
+                "--policy.device=cuda",
+                "--policy.push_to_hub=false",
+                f"--output_dir={output_dir}",
+                "--batch_size=4",
+                "--steps=10",
+                "--eval_freq=-1",
+                "--log_freq=5",
+                "--save_freq=10",
+                "--seed=42",
+                "--num_workers=0",
+            ]
+
+            result = run_accelerate_training(
+                config_args, num_processes=2, temp_dir=temp_dir, distributed_type="FSDP"
+            )
+            assert result.returncode == 0, (
+                f"FSDP training failed:\nSTDOUT:\n{result.stdout}\n\nSTDERR:\n{result.stderr}"
+            )
+
+            # The gathered optimizer state must be written under FSDP (proves the save collective ran),
+            # in the same safetensors format as single-GPU training.
+            training_state_dir = output_dir / "checkpoints" / "last" / "training_state"
+            optimizer_state = training_state_dir / "optimizer_state.safetensors"
+            optimizer_param_groups = training_state_dir / "optimizer_param_groups.json"
+            assert optimizer_state.exists(), f"FSDP optimizer state not saved in {training_state_dir}"
+            assert optimizer_param_groups.exists(), (
+                f"FSDP optimizer param groups not saved in {training_state_dir}"
+            )
+
+            # Resume from the checkpoint for more steps. A successful run proves load_fsdp_optimizer
+            # accepts the saved state and reshards it without shape/key errors.
+            resume_config = output_dir / "checkpoints" / "last" / "pretrained_model" / "train_config.json"
+            resume_args = [
+                f"--config_path={resume_config}",
+                "--resume=true",
+                "--steps=20",
+            ]
+            resume_result = run_accelerate_training(
+                resume_args, num_processes=2, temp_dir=temp_dir, distributed_type="FSDP"
+            )
+            assert resume_result.returncode == 0, (
+                f"FSDP resume failed:\nSTDOUT:\n{resume_result.stdout}\n\nSTDERR:\n{resume_result.stderr}"
+            )
+            assert "End of training" in resume_result.stdout or "End of training" in resume_result.stderr

tests/utils/test_train_utils.py

@@ -136,3 +136,18 @@ def test_save_load_training_state(tmp_path, optimizer, scheduler):
     assert loaded_step == 10
     assert loaded_optimizer is optimizer
     assert loaded_scheduler is scheduler
+
+
+def test_load_training_state_skip_optimizer(tmp_path, optimizer, scheduler):
+    # FSDP loads optimizer separately (after accelerator.prepare)
+    # load_training_state(load_optimizer=False) must restore step + scheduler but leave the
+    # optimizer untouched and never touch the on-disk optimizer state.
+    save_training_state(tmp_path, 10, optimizer, scheduler)
+    with patch("lerobot.common.train_utils.load_optimizer_state") as mock_load_optimizer_state:
+        loaded_step, loaded_optimizer, loaded_scheduler = load_training_state(
+            tmp_path, optimizer, scheduler, load_optimizer=False
+        )
+    mock_load_optimizer_state.assert_not_called()
+    assert loaded_step == 10
+    assert loaded_optimizer is optimizer
+    assert loaded_scheduler is scheduler