make tokenizer/text-encoder model ids configurable + some nits

src/lerobot/policies/fastwam/configuration_fastwam.py

@@ -28,7 +28,9 @@ from lerobot.optim import AdamWConfig
 from lerobot.utils.constants import ACTION, OBS_STATE
 
 WAN22_MODEL_ID = "Wan-AI/Wan2.2-TI2V-5B"
+WAN22_DIFFUSERS_MODEL_ID = "Wan-AI/Wan2.2-TI2V-5B-Diffusers"
 FASTWAM_BASE_MODEL_ID = "lerobot/fastwam_base"
+WAN_T5_TOKENIZER_ID = "google/umt5-xxl"
 
 
 _FASTWAM_VIDEO_BASE_COMPAT_KEYS = (
@@ -99,8 +101,11 @@ def _coerce_enum(enum_cls: type, value: Any) -> Any:
         return value
     try:
         return enum_cls(value)
-    except (TypeError, ValueError):
-        return getattr(enum_cls, str(value), value)
+    except (TypeError, ValueError) as exc:
+        member = getattr(enum_cls, str(value), None)
+        if member is None:
+            raise ValueError(f"Cannot coerce {value!r} into {enum_cls.__name__}.") from exc
+        return member
 
 
 def _coerce_policy_features(features: dict[str, Any] | None) -> dict[str, PolicyFeature] | None:
@@ -184,7 +189,8 @@ class FastWAMConfig(PreTrainedConfig):
     image_size: tuple[int, int] = (224, 448)
     context_len: int = 128
     model_id: str = WAN22_MODEL_ID
-    tokenizer_model_id: str = WAN22_MODEL_ID
+    tokenizer_model_id: str = WAN_T5_TOKENIZER_ID
+    text_encoder_model_id: str = WAN22_DIFFUSERS_MODEL_ID
     base_model_id: str | None = FASTWAM_BASE_MODEL_ID
     tokenizer_max_len: int = 128
     load_text_encoder: bool = True
@@ -229,7 +235,6 @@ class FastWAMConfig(PreTrainedConfig):
         super().__post_init__()
         self.image_size = tuple(self.image_size)
         self.model_id = _validate_wan_model_id(self.model_id, "model_id")
-        self.tokenizer_model_id = _validate_wan_model_id(self.tokenizer_model_id, "tokenizer_model_id")
         self.input_features = _coerce_policy_features(self.input_features)
         self.output_features = _coerce_policy_features(self.output_features)
         self.toggle_action_dimensions = [int(dim) for dim in self.toggle_action_dimensions]

src/lerobot/policies/fastwam/modeling_fastwam.py

@@ -253,7 +253,9 @@ class FastWAMPolicy(PreTrainedPolicy):
             mot_checkpoint_mixed_attn=config.mot_checkpoint_mixed_attn,
         )
         text_encoder = (
-            load_pretrained_wan_text_encoder(torch_dtype=dtype, device=device)
+            load_pretrained_wan_text_encoder(
+                model_id=config.text_encoder_model_id, torch_dtype=dtype, device=device
+            )
             if config.load_text_encoder
             else None
         )
@@ -263,7 +265,9 @@ class FastWAMPolicy(PreTrainedPolicy):
             mot=mot,
             vae=load_pretrained_wan_vae(torch_dtype=dtype, device=device),
             text_encoder=text_encoder,
-            tokenizer=build_wan_tokenizer(tokenizer_max_len=config.tokenizer_max_len),
+            tokenizer=build_wan_tokenizer(
+                model_id=config.tokenizer_model_id, tokenizer_max_len=config.tokenizer_max_len
+            ),
             text_dim=int(config.video_dit_config["text_dim"]),
             proprio_dim=config.proprio_dim,
             device=device,
@@ -279,6 +283,11 @@ class FastWAMPolicy(PreTrainedPolicy):
         )
 
 
+def _scalar(value: Any) -> Any:
+    """Unwrap a 0-/1-element tensor (e.g. from DataLoader collation) to a Python scalar."""
+    return value.item() if isinstance(value, Tensor) else value
+
+
 def _batch_to_infer_kwargs(batch: dict[str, Tensor], config: FastWAMConfig) -> dict[str, Any]:
     return {
         "prompt": _prompt_from_batch(batch=batch, config=config),
@@ -288,8 +297,8 @@ def _batch_to_infer_kwargs(batch: dict[str, Tensor], config: FastWAMConfig) -> d
         "context": batch.get("context"),
         "context_mask": batch.get("context_mask"),
         "negative_prompt": batch.get("negative_prompt", config.negative_prompt),
-        "text_cfg_scale": float(batch.get("text_cfg_scale", config.text_cfg_scale)),
-        "num_inference_steps": int(batch.get("num_inference_steps", config.num_inference_steps)),
+        "text_cfg_scale": float(_scalar(batch.get("text_cfg_scale", config.text_cfg_scale))),
+        "num_inference_steps": int(_scalar(batch.get("num_inference_steps", config.num_inference_steps))),
         "sigma_shift": batch.get("sigma_shift", config.sigma_shift),
         "seed": batch.get("seed", config.inference_seed),
         "rand_device": batch.get("rand_device", config.rand_device),

src/lerobot/policies/fastwam/modular_fastwam.py

@@ -26,6 +26,8 @@ import torch.nn.functional as functional
 from PIL import Image
 
 from .wan_components import (
+    WAN22_DIFFUSERS_MODEL_ID,
+    WAN_T5_TOKENIZER,
     build_wan_tokenizer,
     load_pretrained_wan_text_encoder,
     load_pretrained_wan_vae,
@@ -938,7 +940,8 @@ class FastWAM(torch.nn.Module):
         device: str = "cuda",
         torch_dtype: torch.dtype = torch.bfloat16,
         model_id: str = "Wan-AI/Wan2.2-TI2V-5B",
-        tokenizer_model_id: str = "Wan-AI/Wan2.2-TI2V-5B",
+        tokenizer_model_id: str = WAN_T5_TOKENIZER,
+        text_encoder_model_id: str = WAN22_DIFFUSERS_MODEL_ID,
         tokenizer_max_len: int = 512,
         load_text_encoder: bool = True,
         proprio_dim: int | None = None,
@@ -958,7 +961,6 @@ class FastWAM(torch.nn.Module):
             raise ValueError("`video_dit_config` is required for FastWAM.from_wan22_pretrained().")
         if "text_dim" not in video_dit_config:
             raise ValueError("`video_dit_config['text_dim']` is required for FastWAM.")
-        del tokenizer_model_id  # tokenizer is the stock UMT5 one (google/umt5-xxl)
 
         # Custom MoT video DiT from the original Wan2.2 repo; frozen VAE / UMT5 from
         # the diffusers conversion. This is the offline base-creation path; the
@@ -984,11 +986,13 @@ class FastWAM(torch.nn.Module):
 
         vae = load_pretrained_wan_vae(torch_dtype=torch_dtype, device=device)
         text_encoder = (
-            load_pretrained_wan_text_encoder(torch_dtype=torch_dtype, device=device)
+            load_pretrained_wan_text_encoder(
+                model_id=text_encoder_model_id, torch_dtype=torch_dtype, device=device
+            )
             if load_text_encoder
             else None
         )
-        tokenizer = build_wan_tokenizer(tokenizer_max_len=tokenizer_max_len)
+        tokenizer = build_wan_tokenizer(model_id=tokenizer_model_id, tokenizer_max_len=tokenizer_max_len)
 
         return cls(
             video_expert=video_expert,

src/lerobot/policies/fastwam/wan_components.py

@@ -36,10 +36,6 @@ if TYPE_CHECKING or _diffusers_available:
 else:
     AutoencoderKLWan = None
 
-if TYPE_CHECKING:
-    from .wan_adapters import WanVideoVAE38
-    from .wan_video_dit import WanVideoDiT
-
 from .wan_adapters import WanVideoVAE38
 from .wan_video_dit import WanVideoDiT
 
@@ -109,8 +105,8 @@ class WanTokenizer:
         return out.input_ids
 
 
-def build_wan_tokenizer(*, tokenizer_max_len: int) -> WanTokenizer:
-    return WanTokenizer(name=WAN_T5_TOKENIZER, seq_len=int(tokenizer_max_len))
+def build_wan_tokenizer(*, model_id: str = WAN_T5_TOKENIZER, tokenizer_max_len: int) -> WanTokenizer:
+    return WanTokenizer(name=model_id, seq_len=int(tokenizer_max_len))
 
 
 def load_pretrained_wan_vae(*, torch_dtype: torch.dtype, device: str) -> WanVideoVAE38:
@@ -120,12 +116,20 @@ def load_pretrained_wan_vae(*, torch_dtype: torch.dtype, device: str) -> WanVide
     return WanVideoVAE38(dtype=torch_dtype, device=device, pretrained=vae)
 
 
-def load_pretrained_wan_text_encoder(*, torch_dtype: torch.dtype, device: str) -> WanTextEncoder:
-    """Load real UMT5-XXL encoder weights from the diffusers repo (offline base creation)."""
+def load_pretrained_wan_text_encoder(
+    *,
+    model_id: str = WAN22_DIFFUSERS_MODEL_ID,
+    subfolder: str | None = "text_encoder",
+    torch_dtype: torch.dtype,
+    device: str,
+) -> WanTextEncoder:
+    """Load UMT5-XXL encoder weights (defaults to the Wan2.2 diffusers repo).
+
+    Must stay compatible with the tokenizer (see `build_wan_tokenizer`): the encoder's
+    embedding table is indexed by the tokenizer's vocabulary.
+    """
     require_package("transformers", extra="fastwam")
-    encoder = UMT5EncoderModel.from_pretrained(
-        WAN22_DIFFUSERS_MODEL_ID, subfolder="text_encoder", torch_dtype=torch_dtype
-    )
+    encoder = UMT5EncoderModel.from_pretrained(model_id, subfolder=subfolder, torch_dtype=torch_dtype)
     return WanTextEncoder(dtype=torch_dtype, device=device, pretrained=encoder)
 
 

tests/policies/fastwam/test_fastwam_policy.py

@@ -73,8 +73,9 @@ def test_config_validates_features_model_ids_and_saved_auto_route(tmp_path):
     assert cfg.robot_state_feature.shape == (8,)
     with pytest.raises(ValueError, match="image feature"):
         FastWAMConfig(input_features={OBS_STATE: PolicyFeature(type=FeatureType.STATE, shape=(8,))})
-    with pytest.raises(ValueError, match="tokenizer_model_id"):
-        FastWAMConfig(tokenizer_model_id="somebody/other-tokenizer")
+    assert FastWAMConfig(tokenizer_model_id="somebody/other-tokenizer").tokenizer_model_id == (
+        "somebody/other-tokenizer"
+    )
 
 
 def test_preprocessor_passes_images_through_and_postprocessor_toggles_actions(tmp_path):