run precommit and fix issues

Fast tests currently fail because of the missing dependency.

docs/source/_toctree.yml

@@ -19,6 +19,8 @@
     title: Train RL in Simulation
   - local: multi_gpu_training
     title: Multi GPU training
+  - local: peft_training
+    title: Training with PEFT (e.g., LoRA)
   title: "Tutorials"
 - sections:
   - local: lerobot-dataset-v3

docs/source/peft_training.mdx

@@ -0,0 +1,62 @@
+# Parameter efficient fine-tuning with 🤗 PEFT
+
+[🤗 PEFT](https://github.com/huggingface/peft) (Parameter-Efficient Fine-Tuning) is a library for efficiently adapting
+large pretrained models such as pre-trained policies (e.g., SmolVLA, π₀, ...) to new tasks without training all
+of the model's parameters while yielding comparable performance.
+
+Install the `lerobot[peft]` optional package to enable PEFT support.
+
+To read about all the possible methods of adaption, please refer to the [🤗 PEFT docs](https://huggingface.co/docs/peft/index).
+
+## Training SmolVLA
+
+In this section we'll show you how to train a pre-trained SmolVLA policy with PEFT on the libero dataset.
+For brevity we're only training on the `libero_spatial` subset. We will use `lerobot/smolvla_base` as the model
+to parameter efficiently fine-tune:
+
+```
+lerobot-train \
+ --policy.path=lerobot/smolvla_base \
+ --policy.repo_id=your_hub_name/my_libero_smolvla \
+ --dataset.repo_id=HuggingFaceVLA/libero \
+ --policy.output_features=null \
+ --policy.input_features=null \
+ --policy.optimizer_lr=1e-3 \
+ --policy.scheduler_decay_lr=1e-4 \
+ --env.type=libero \
+ --env.task=libero_spatial \
+ --steps=100000 \
+ --batch_size=32 \
+ --peft.method_type=LORA \
+ --peft.r=64
+```
+
+Note the `--peft.method_type` parameter that let's you select which PEFT method to use. Here we use
+[LoRA](https://huggingface.co/docs/peft/main/en/package_reference/lora) (Low-Rank Adapter) which is probably the most
+popular fine-tuning method to date. Low-rank adaption means that we only fine-tune a matrix with comparably low rank
+instead of the full weight matrix. This rank can be specified using the `--peft.r` parameter. The higher the rank
+the closer you get to full fine-tuning
+
+There are more complex methods that have more parameters. These are not yet supported, feel free to raise an issue
+if you want to see a specific PEFT method supported.
+
+By default, PEFT will target the `q_proj` and `v_proj` layers of the LM expert in SmolVLA. It will also target the
+state and action projection matrices as they are most likely task-dependent. If you need to target different layers
+you can use `--peft.target_modules` to specify which layers to target. You can refer to the respective PEFT method's
+documentation to see what inputs are supported, (e.g., [LoRA's target_modules documentation](https://huggingface.co/docs/peft/main/en/package_reference/lora#peft.LoraConfig.target_modules)).
+Usually a list of suffixes or a regex are supported. For example, to target the MLPs of the `lm_expert` instead of
+the `q` and `v` projections, use:
+
+```
+--peft.target_modules='(model\.vlm_with_expert\.lm_expert\..*\.(down|gate|up)_proj|.*\.(state_proj|action_in_proj|action_out_proj|action_time_mlp_in|action_time_mlp_out))'
+```
+
+In case you need to fully fine-tune a layer instead of just adapting it, you can supply a list of layer suffixes
+to the `--peft.full_training_modules` parameter:
+
+```
+--peft.full_training_modules=["state_proj"]
+```
+
+The learning rate and the scheduled target learning rate can usually be scaled by a factor of 10 compared to the
+learning rate used for full fine-tuning (e.g., 1e-4 normal, so 1e-3 using LoRA).

examples/rtc/eval_with_real_robot.py

@@ -455,7 +455,18 @@ def demo_cli(cfg: RTCDemoConfig):
     if cfg.policy.type == "pi05" or cfg.policy.type == "pi0":
         config.compile_model = cfg.use_torch_compile
 
-    policy = policy_class.from_pretrained(cfg.policy.pretrained_path, config=config)
+    if config.use_peft:
+        from peft import PeftConfig, PeftModel
+
+        peft_pretrained_path = cfg.policy.pretrained_path
+        peft_config = PeftConfig.from_pretrained(peft_pretrained_path)
+
+        policy = policy_class.from_pretrained(
+            pretrained_name_or_path=peft_config.base_model_name_or_path, config=config
+        )
+        policy = PeftModel.from_pretrained(policy, peft_pretrained_path, config=peft_config)
+    else:
+        policy = policy_class.from_pretrained(cfg.policy.pretrained_path, config=config)
 
     # Turn on RTC
     policy.config.rtc_config = cfg.rtc

pyproject.toml

@@ -146,6 +146,7 @@ hilserl = ["lerobot[transformers-dep]", "gym-hil>=0.1.13,<0.2.0", "lerobot[grpci
 
 # Features
 async = ["lerobot[grpcio-dep]", "matplotlib>=3.10.3,<4.0.0"]
+peft = ["lerobot[transformers-dep]", "peft>=0.18.0"]
 
 # Development
 dev = ["pre-commit>=3.7.0,<5.0.0", "debugpy>=1.8.1,<1.9.0", "lerobot[grpcio-dep]", "grpcio-tools==1.73.1", "mypy>=1.19.1"]
@@ -182,7 +183,8 @@ all = [
     "lerobot[phone]",
     "lerobot[libero]",
     "lerobot[metaworld]",
-    "lerobot[sarm]"
+    "lerobot[sarm]",
+    "lerobot[peft]",
 ]
 
 [project.scripts]

src/lerobot/configs/default.py

@@ -67,3 +67,31 @@ class EvalConfig:
                 f"to increase the number of episodes to match the batch size (e.g. `eval.n_episodes={self.batch_size}`), "
                 f"or lower the batch size (e.g. `eval.batch_size={self.n_episodes}`)."
             )
+
+
+@dataclass
+class PeftConfig:
+    # PEFT offers many fine-tuning methods, layer adapters being the most common and currently also the most
+    # effective methods so we'll focus on those in this high-level config interface.
+
+    # Either a string (module name suffix or 'all-linear'), a list of module name suffixes or a regular expression
+    # describing module names to target with the configured PEFT method. Some policies have a default value for this
+    # so that you don't *have* to choose which layers to adapt but it might still be worthwhile depending on your case.
+    target_modules: list[str] | str | None = None
+
+    # Names/suffixes of modules to fully fine-tune and store alongside adapter weights. Useful for layers that are
+    # not part of a pre-trained model (e.g., action state projections). Depending on the policy this defaults to layers
+    # that are newly created in pre-trained policies. If you're fine-tuning an already trained policy you might want
+    # to set this to `[]`. Corresponds to PEFT's `modules_to_save`.
+    full_training_modules: list[str] | None = None
+
+    # The PEFT (adapter) method to apply to the policy. Needs to be a valid PEFT type.
+    method_type: str = "LORA"
+
+    # Adapter initialization method. Look at the specific PEFT adapter documentation for defaults.
+    init_type: str | None = None
+
+    # We expect that all PEFT adapters are in some way doing rank-decomposition therefore this parameter specifies
+    # the rank used for the adapter. In general a higher rank means more trainable parameters and closer to full
+    # fine-tuning.
+    r: int = 16

src/lerobot/configs/policies.py

@@ -55,14 +55,18 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):  # type: igno
 
     n_obs_steps: int = 1
 
-    input_features: dict[str, PolicyFeature] = field(default_factory=dict)
-    output_features: dict[str, PolicyFeature] = field(default_factory=dict)
+    # `input_features` can be set to None/null in order to infer those values from the dataset.
+    input_features: dict[str, PolicyFeature] | None = field(default_factory=dict)
+    output_features: dict[str, PolicyFeature] | None = field(default_factory=dict)
 
     device: str | None = None  # e.g. "cuda", "cuda:0", "cpu", or "mps"
     # `use_amp` determines whether to use Automatic Mixed Precision (AMP) for training and evaluation. With AMP,
     # automatic gradient scaling is used.
     use_amp: bool = False
 
+    # Whether the policy employed PEFT for training.
+    use_peft: bool = False
+
     push_to_hub: bool = True  # type: ignore[assignment] # TODO: use a different name to avoid override
     repo_id: str | None = None
 
@@ -125,6 +129,8 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):  # type: igno
 
     @property
     def robot_state_feature(self) -> PolicyFeature | None:
+        if self.input_features is None:
+            return None
         for ft_name, ft in self.input_features.items():
             if ft.type is FeatureType.STATE and ft_name == OBS_STATE:
                 return ft
@@ -132,6 +138,8 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):  # type: igno
 
     @property
     def env_state_feature(self) -> PolicyFeature | None:
+        if self.input_features is None:
+            return None
         for _, ft in self.input_features.items():
             if ft.type is FeatureType.ENV:
                 return ft
@@ -139,10 +147,14 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):  # type: igno
 
     @property
     def image_features(self) -> dict[str, PolicyFeature]:
+        if self.input_features is None:
+            return {}
         return {key: ft for key, ft in self.input_features.items() if ft.type is FeatureType.VISUAL}
 
     @property
     def action_feature(self) -> PolicyFeature | None:
+        if self.output_features is None:
+            return None
         for ft_name, ft in self.output_features.items():
             if ft.type is FeatureType.ACTION and ft_name == ACTION:
                 return ft

src/lerobot/configs/train.py

@@ -24,7 +24,7 @@ from huggingface_hub.errors import HfHubHTTPError
 
 from lerobot import envs
 from lerobot.configs import parser
-from lerobot.configs.default import DatasetConfig, EvalConfig, WandBConfig
+from lerobot.configs.default import DatasetConfig, EvalConfig, PeftConfig, WandBConfig
 from lerobot.configs.policies import PreTrainedConfig
 from lerobot.optim import OptimizerConfig
 from lerobot.optim.schedulers import LRSchedulerConfig
@@ -65,6 +65,7 @@ class TrainPipelineConfig(HubMixin):
     scheduler: LRSchedulerConfig | None = None
     eval: EvalConfig = field(default_factory=EvalConfig)
     wandb: WandBConfig = field(default_factory=WandBConfig)
+    peft: PeftConfig | None = None
 
     # RA-BC (Reward-Aligned Behavior Cloning) parameters
     use_rabc: bool = False  # Enable reward-weighted training

src/lerobot/policies/factory.py

@@ -471,11 +471,40 @@ def make_policy(
     if ds_meta is not None:
         kwargs["dataset_meta"] = ds_meta
 
-    if cfg.pretrained_path:
+    if not cfg.pretrained_path and cfg.use_peft:
+        raise ValueError(
+            "Instantiating a policy with `use_peft=True` without a checkpoint is not supported since that requires "
+            "the PEFT config parameters to be set. For training with PEFT, see `lerobot_train.py` on how to do that."
+        )
+
+    if cfg.pretrained_path and not cfg.use_peft:
         # 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
         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
+        # of the adapter and the adapter's config contains the path to the base policy. So we need the
+        # adapter config first, then load the correct policy and then apply PEFT.
+        from peft import PeftConfig, PeftModel
+
+        logging.info("Loading policy's PEFT adapter.")
+
+        peft_pretrained_path = cfg.pretrained_path
+        peft_config = PeftConfig.from_pretrained(peft_pretrained_path)
+
+        kwargs["pretrained_name_or_path"] = peft_config.base_model_name_or_path
+        if not kwargs["pretrained_name_or_path"]:
+            # This means that there's a bug or we trained a policy from scratch using PEFT.
+            # It is more likely that this is a bug so we'll raise an error.
+            raise ValueError(
+                "No pretrained model name found in adapter config. Can't instantiate the pre-trained policy on which "
+                "the adapter was trained."
+            )
+
+        policy = policy_cls.from_pretrained(**kwargs)
+        policy = PeftModel.from_pretrained(policy, peft_pretrained_path, config=peft_config)
+
     else:
         # Make a fresh policy.
         policy = policy_cls(**kwargs)

src/lerobot/policies/pretrained.py

@@ -206,6 +206,7 @@ class PreTrainedPolicy(nn.Module, HubMixin, abc.ABC):
     def push_model_to_hub(
         self,
         cfg: TrainPipelineConfig,
+        peft_model=None,
     ):
         api = HfApi()
         repo_id = api.create_repo(
@@ -216,7 +217,14 @@ class PreTrainedPolicy(nn.Module, HubMixin, abc.ABC):
         with TemporaryDirectory(ignore_cleanup_errors=True) as tmp:
             saved_path = Path(tmp) / repo_id
 
-            self.save_pretrained(saved_path)  # Calls _save_pretrained and stores model tensors
+            if peft_model is not None:
+                # Since PEFT just forwards calls to `push_model_to_hub`, `self` is not the PeftModel wrapper
+                # but the actual policy which is why we need the PEFT model passed to us to save the adapter.
+                # That also means that we need to store the policy config ourselves since PEFT can't.
+                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
 
             card = self.generate_model_card(
                 cfg.dataset.repo_id, self.config.type, self.config.license, self.config.tags

src/lerobot/rl/wandb_utils.py

@@ -112,7 +112,32 @@ class WandBLogger:
         artifact_name = f"{self._group}-{step_id}"
         artifact_name = get_safe_wandb_artifact_name(artifact_name)
         artifact = self._wandb.Artifact(artifact_name, type="model")
-        artifact.add_file(checkpoint_dir / PRETRAINED_MODEL_DIR / SAFETENSORS_SINGLE_FILE)
+        pretrained_model_dir = checkpoint_dir / PRETRAINED_MODEL_DIR
+
+        # Check if this is a PEFT model (has adapter files instead of model.safetensors)
+        adapter_model_file = pretrained_model_dir / "adapter_model.safetensors"
+        standard_model_file = pretrained_model_dir / SAFETENSORS_SINGLE_FILE
+
+        if adapter_model_file.exists():
+            # PEFT model: add adapter files and configs
+            artifact.add_file(adapter_model_file)
+            adapter_config_file = pretrained_model_dir / "adapter_config.json"
+            if adapter_config_file.exists():
+                artifact.add_file(adapter_config_file)
+            # Also add the policy config which is needed for loading
+            config_file = pretrained_model_dir / "config.json"
+            if config_file.exists():
+                artifact.add_file(config_file)
+        elif standard_model_file.exists():
+            # Standard model: add the single safetensors file
+            artifact.add_file(standard_model_file)
+        else:
+            logging.warning(
+                f"No {SAFETENSORS_SINGLE_FILE} or adapter_model.safetensors found in {pretrained_model_dir}. "
+                "Skipping model artifact upload to WandB."
+            )
+            return
+
         self._wandb.log_artifact(artifact)
 
     def log_dict(

src/lerobot/scripts/lerobot_eval.py

@@ -278,9 +278,17 @@ def eval_policy(
         raise ValueError("If max_episodes_rendered > 0, videos_dir must be provided.")
 
     if not isinstance(policy, PreTrainedPolicy):
-        raise ValueError(
-            f"Policy of type 'PreTrainedPolicy' is expected, but type '{type(policy)}' was provided."
-        )
+        try:
+            from peft import PeftModel
+
+            if not isinstance(policy, PeftModel):
+                raise ValueError(
+                    f"Policy of type 'PreTrainedPolicy' is expected, but type '{type(policy)}' was provided."
+                )
+        except ImportError:
+            raise ValueError(
+                "PEFT is required to evaluate a PEFT-trained policy. Please install PEFT using `pip install peft`."
+            ) from None
 
     start = time.time()
     policy.eval()

src/lerobot/scripts/lerobot_record.py

@@ -193,8 +193,10 @@ class RecordConfig:
     def __post_init__(self):
         # HACK: We parse again the cli args here to get the pretrained path if there was one.
         policy_path = parser.get_path_arg("policy")
+
         if policy_path:
             cli_overrides = parser.get_cli_overrides("policy")
+
             self.policy = PreTrainedConfig.from_pretrained(policy_path, cli_overrides=cli_overrides)
             self.policy.pretrained_path = policy_path
 

src/lerobot/scripts/lerobot_train.py

@@ -13,6 +13,7 @@
 # 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 dataclasses
 import logging
 import time
 from contextlib import nullcontext
@@ -147,6 +148,92 @@ def update_policy(
     return train_metrics, output_dict
 
 
+def get_default_peft_configuration(policy_type):
+    """Build a basic PEFT configuration for the given policy type assuming that we train a policy from a checkpoint."""
+
+    common_projections = "state_proj|action_in_proj|action_out_proj|action_time_mlp_in|action_time_mlp_out"
+
+    if policy_type == "smolvla":
+        return {
+            "target_modules": rf"(model\.vlm_with_expert\.lm_expert\..*\.(q|v)_proj|model\.({common_projections}))",
+            "modules_to_save": [],
+        }
+    elif policy_type in ("pi0", "pi05"):
+        return {
+            "target_modules": rf"(.*\.gemma_expert\..*\.self_attn.(q|v)_proj|model\.({common_projections}))",
+            "modules_to_save": [],
+        }
+
+    return {"modules_to_save": None}
+
+
+def wrap_policy_in_peft_model(cfg, policy):
+    from peft import PEFT_TYPE_TO_CONFIG_MAPPING, PeftType, get_peft_model
+
+    # Disable all gradients because we'll only train the parameters selected by the PEFT method.
+    # Layers that should receive gradients anyway need to be listed in `modules_to_save`.
+    for p in policy.parameters():
+        p.requires_grad_(False)
+
+    if not cfg.policy.pretrained_path:
+        raise ValueError(
+            "Training from scratch using PEFT. This is unlikely to yield good results. "
+            "Supply a `policy.path` to fine-tune an existing model."
+        )
+
+    if cfg.policy.type == "smolvla" and not cfg.policy.load_vlm_weights:
+        logging.warning(
+            "Training SmolVLA from scratch using PEFT. This is unlikely to yield good results. Set "
+            "`load_vlm_weights=True` to fine-tune the existing policy."
+        )
+
+    peft_config_policy = get_default_peft_configuration(cfg.policy.type)
+    peft_config_cli = dataclasses.asdict(cfg.peft) if cfg.peft else {}
+    peft_config_cli["modules_to_save"] = peft_config_cli["full_training_modules"]  # compatibility with PEFT
+    peft_method_type = PeftType[peft_config_cli["method_type"].upper()]
+    peft_config_cls = PEFT_TYPE_TO_CONFIG_MAPPING[peft_method_type]
+
+    # Handle specific CLI overrides
+    for key in ["target_modules", "modules_to_save", "r"]:
+        if peft_config_cli[key] is not None:
+            peft_config_policy[key] = peft_config_cli[key]
+
+    if "target_modules" not in peft_config_policy:
+        raise ValueError(
+            f"There is no default `target_modules` value for policy {cfg.policy.type}. Please pass it manually."
+        )
+
+    # Init method depends on the used PEFT method, your specific PEFT method
+    # might not be considered here, in that case an error is raised.
+    if peft_config_cli["init_type"] is not None:
+        if peft_method_type == "LORA":
+            peft_config_policy["init_lora_weights"] = peft_config_cli["init_type"]
+        elif peft_method_type == "MISS":
+            peft_config_policy["init_weights"] = peft_config_cli["init_type"]
+        else:
+            raise ValueError(
+                f"Init type {peft_config_cli['init_type']} unknown for PEFT method {peft_method_type}."
+            )
+
+    # PEFT uses this attribute to set adapter_config.base_name_or_path which we use for loading the
+    # correct base model in `make_policy` since in a PEFT loading setting we only get the path to the
+    # adapter, not the base model.
+    if policy.config.pretrained_path:
+        policy.name_or_path = str(policy.config.pretrained_path)
+
+    # Finally wrap the policy in a PEFT model
+    policy = get_peft_model(
+        policy,
+        peft_config_cls(**peft_config_policy),
+    )
+
+    # Make sure that the config is tagged as using PEFT so that the loading code can take the
+    # appropriate steps to use the adapter weights and the PEFT config instead of the full model weights.
+    policy.config.use_peft = True
+
+    return policy
+
+
 @parser.wrap()
 def train(cfg: TrainPipelineConfig, accelerator: Accelerator | None = None):
     """
@@ -230,6 +317,10 @@ def train(cfg: TrainPipelineConfig, accelerator: Accelerator | None = None):
         rename_map=cfg.rename_map,
     )
 
+    if cfg.peft is not None:
+        logging.info("Using PEFT! Wrapping model.")
+        policy = wrap_policy_in_peft_model(cfg, policy)
+
     # Wait for all processes to finish policy creation before continuing
     accelerator.wait_for_everyone()
 
@@ -502,7 +593,10 @@ def train(cfg: TrainPipelineConfig, accelerator: Accelerator | None = None):
 
         if cfg.policy.push_to_hub:
             unwrapped_policy = accelerator.unwrap_model(policy)
-            unwrapped_policy.push_model_to_hub(cfg)
+            if cfg.policy.use_peft:
+                unwrapped_policy.push_model_to_hub(cfg, peft_model=unwrapped_policy)
+            else:
+                unwrapped_policy.push_model_to_hub(cfg)
             preprocessor.push_to_hub(cfg.policy.repo_id)
             postprocessor.push_to_hub(cfg.policy.repo_id)
 

src/lerobot/utils/train_utils.py

@@ -99,6 +99,10 @@ def save_checkpoint(
     pretrained_dir = checkpoint_dir / PRETRAINED_MODEL_DIR
     policy.save_pretrained(pretrained_dir)
     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
+        # policy config which we need for loading the model. In this case we'll write it ourselves.
+        policy.config.save_pretrained(pretrained_dir)
     if preprocessor is not None:
         preprocessor.save_pretrained(pretrained_dir)
     if postprocessor is not None:

tests/test_cli.py

@@ -0,0 +1,229 @@
+import importlib
+import os
+from unittest.mock import MagicMock, patch
+
+import pytest
+from safetensors.torch import load_file
+
+from .utils import require_package
+
+
+def run_command(cmd, module, args):
+    module = importlib.import_module(f"lerobot.scripts.{module}")
+    with patch("sys.argv", [cmd] + args):
+        module.main()
+
+
+def lerobot_train(args):
+    return run_command(cmd="lerobot-train", module="lerobot_train", args=args)
+
+
+def lerobot_record(args):
+    return run_command(cmd="lerobot-record", module="lerobot_record", args=args)
+
+
+def resolve_model_id_for_peft_training(policy_type):
+    """PEFT training needs pretrained models, this finds the pretrained model of a policy type for PEFT training."""
+    if policy_type == "smolvla":
+        return "lerobot/smolvla_base"
+
+    raise ValueError(f"No pretrained model known for {policy_type}. PEFT training will not work.")
+
+
+@pytest.mark.parametrize("policy_type", ["smolvla"])
+@require_package("peft")
+def test_peft_training_push_to_hub_works(policy_type, tmp_path):
+    """Ensure that push to hub stores PEFT only the adapter, not the full model weights."""
+    output_dir = tmp_path / f"output_{policy_type}"
+    upload_folder_contents = set()
+
+    model_id = resolve_model_id_for_peft_training(policy_type)
+
+    def mock_upload_folder(*args, **kwargs):
+        folder_path = kwargs["folder_path"]
+        # we include more than is actually uploaded since we ignore {allow,ignore}_patterns of upload_folders()
+        upload_folder_contents.update(os.listdir(folder_path))
+        return MagicMock()
+
+    with (
+        patch("huggingface_hub.HfApi.create_repo"),
+        patch("huggingface_hub.HfApi.upload_folder", mock_upload_folder),
+    ):
+        lerobot_train(
+            [
+                f"--policy.path={model_id}",
+                "--policy.push_to_hub=true",
+                "--policy.repo_id=foo/bar",
+                "--policy.input_features=null",
+                "--policy.output_features=null",
+                "--peft.method=LORA",
+                "--dataset.repo_id=lerobot/pusht",
+                "--dataset.episodes=[0, 1]",
+                "--steps=1",
+                f"--output_dir={output_dir}",
+            ]
+        )
+
+        assert "adapter_model.safetensors" in upload_folder_contents
+        assert "config.json" in upload_folder_contents
+        assert "adapter_config.json" in upload_folder_contents
+
+
+@pytest.mark.parametrize("policy_type", ["smolvla"])
+@require_package("peft")
+def test_peft_training_works(policy_type, tmp_path):
+    """Check whether the standard case of fine-tuning a (partially) pre-trained policy with PEFT works."""
+    output_dir = tmp_path / f"output_{policy_type}"
+    model_id = resolve_model_id_for_peft_training(policy_type)
+
+    lerobot_train(
+        [
+            f"--policy.path={model_id}",
+            "--policy.push_to_hub=false",
+            "--policy.input_features=null",
+            "--policy.output_features=null",
+            "--peft.method=LORA",
+            "--dataset.repo_id=lerobot/pusht",
+            "--dataset.episodes=[0, 1]",
+            "--steps=1",
+            f"--output_dir={output_dir}",
+        ]
+    )
+
+    policy_dir = output_dir / "checkpoints" / "last" / "pretrained_model"
+
+    for file in ["adapter_config.json", "adapter_model.safetensors", "config.json"]:
+        assert (policy_dir / file).exists()
+
+    # This is the default case where we train a pre-trained policy from scratch with new data.
+    # We assume that we target policy-specific modules but fully fine-tune action and state projections
+    # so these must be part of the trained state dict.
+    state_dict = load_file(policy_dir / "adapter_model.safetensors")
+
+    adapted_keys = [
+        "state_proj",
+        "action_in_proj",
+        "action_out_proj",
+        "action_time_mlp_in",
+        "action_time_mlp_out",
+    ]
+
+    found_keys = [
+        module_key
+        for module_key in adapted_keys
+        for state_dict_key in state_dict
+        if f".{module_key}." in state_dict_key
+    ]
+
+    assert set(found_keys) == set(adapted_keys)
+
+
+@pytest.mark.parametrize("policy_type", ["smolvla"])
+@require_package("peft")
+def test_peft_training_params_are_fewer(policy_type, tmp_path):
+    """Check whether the standard case of fine-tuning a (partially) pre-trained policy with PEFT works."""
+    output_dir = tmp_path / f"output_{policy_type}"
+    model_id = resolve_model_id_for_peft_training(policy_type)
+
+    def dummy_update_policy(
+        train_metrics, policy, batch, optimizer, grad_clip_norm: float, accelerator, **kwargs
+    ):
+        params_total = sum(p.numel() for p in policy.parameters())
+        params_trainable = sum(p.numel() for p in policy.parameters() if p.requires_grad)
+
+        assert params_total > params_trainable
+
+        return train_metrics, {}
+
+    with patch("lerobot.scripts.lerobot_train.update_policy", dummy_update_policy):
+        lerobot_train(
+            [
+                f"--policy.path={model_id}",
+                "--policy.push_to_hub=false",
+                "--policy.input_features=null",
+                "--policy.output_features=null",
+                "--peft.method=LORA",
+                "--dataset.repo_id=lerobot/pusht",
+                "--dataset.episodes=[0, 1]",
+                "--steps=1",
+                f"--output_dir={output_dir}",
+            ]
+        )
+
+
+class DummyRobot:
+    name = "dummy"
+    cameras = []
+    action_features = {"foo": 1.0, "bar": 2.0}
+    observation_features = {"obs1": 1.0, "obs2": 2.0}
+    is_connected = True
+
+    def connect(self, *args):
+        pass
+
+    def disconnect(self):
+        pass
+
+
+def dummy_make_robot_from_config(*args, **kwargs):
+    return DummyRobot()
+
+
+@pytest.mark.parametrize("policy_type", ["smolvla"])
+@require_package("peft")
+def test_peft_record_loads_policy(policy_type, tmp_path):
+    """Train a policy with PEFT and attempt to load it with `lerobot-record`."""
+    from peft import PeftModel
+
+    output_dir = tmp_path / f"output_{policy_type}"
+    model_id = resolve_model_id_for_peft_training(policy_type)
+
+    lerobot_train(
+        [
+            f"--policy.path={model_id}",
+            "--policy.push_to_hub=false",
+            "--policy.input_features=null",
+            "--policy.output_features=null",
+            "--peft.method=LORA",
+            "--dataset.repo_id=lerobot/pusht",
+            "--dataset.episodes=[0, 1]",
+            "--steps=1",
+            f"--output_dir={output_dir}",
+        ]
+    )
+
+    policy_dir = output_dir / "checkpoints" / "last" / "pretrained_model"
+    dataset_dir = tmp_path / "eval_pusht"
+    single_task = "move the table"
+    loaded_policy = None
+
+    def dummy_record_loop(*args, **kwargs):
+        nonlocal loaded_policy
+
+        if "dataset" not in kwargs:
+            return
+
+        dataset = kwargs["dataset"]
+        dataset.add_frame({"task": single_task})
+        loaded_policy = kwargs["policy"]
+
+    with (
+        patch("lerobot.robots.make_robot_from_config", dummy_make_robot_from_config),
+        # disable record loop since we're only interested in successful loading of the policy.
+        patch("lerobot.scripts.lerobot_record.record_loop", dummy_record_loop),
+        # disable speech output
+        patch("lerobot.utils.utils.say"),
+    ):
+        lerobot_record(
+            [
+                f"--policy.path={policy_dir}",
+                "--robot.type=so101_follower",
+                "--robot.port=/dev/null",
+                "--dataset.repo_id=lerobot/eval_pusht",
+                f'--dataset.single_task="{single_task}"',
+                f"--dataset.root={dataset_dir}",
+                "--dataset.push_to_hub=false",
+            ]
+        )
+
+        assert isinstance(loaded_policy, PeftModel)

tests/utils/test_train_utils.py

@@ -82,6 +82,20 @@ def test_save_checkpoint(mock_save_training_state, tmp_path, optimizer):
     mock_save_training_state.assert_called_once()
 
 
+@patch("lerobot.utils.train_utils.save_training_state")
+def test_save_checkpoint_peft(mock_save_training_state, tmp_path, optimizer):
+    policy = Mock()
+    policy.config = Mock()
+    policy.config.save_pretrained = Mock()
+    cfg = Mock()
+    cfg.use_peft = True
+    save_checkpoint(tmp_path, 10, cfg, policy, optimizer)
+    policy.save_pretrained.assert_called_once()
+    cfg.save_pretrained.assert_called_once()
+    policy.config.save_pretrained.assert_called_once()
+    mock_save_training_state.assert_called_once()
+
+
 def test_save_training_state(tmp_path, optimizer, scheduler):
     save_training_state(tmp_path, 10, optimizer, scheduler)
     assert (tmp_path / TRAINING_STATE_DIR).is_dir()