sgl-project/sglang · error · ValueError

Native diffusion LoRA loading requires a safetensors file…

Error message

Native diffusion LoRA loading requires a safetensors file, got {selected_file!r}

What it means

After resolving a LoRA weight (local or remote inventory), maybe_download_lora enforces that the selected file is a .safetensors file because the native diffusion LoRA loader only parses safetensors. Any other extension (.bin, .ckpt, .pt) raises ValueError.

Solutions

  1. Convert the LoRA to safetensors (e.g. diffusers' script or safetensors conversion tools) and specify the new weight name
  2. Download/use the safetensors variant of the same LoRA if the repo offers one

Example fix

# before
load_lora_adapter(repo, weight_name="pytorch_lora_weights.bin")
# after
# convert first: python convert_lora_to_safetensors ...
load_lora_adapter(repo, weight_name="pytorch_lora_weights.safetensors")
Defensive patterns

Strategy: validation

Validate before calling

assert selected.endswith('.safetensors'), f'need safetensors, got {selected}'

Try / catch

try:
    load_lora_adapter(...)
except ValueError as e:
    if 'requires a safetensors file' in str(e):
        convert_to_safetensors(selected_file)

Prevention

When it happens

Trigger: Calling load_lora_adapter where resolve_weight picks a .bin/.ckpt/.pt file — either because weight_name pointed at one, or the best-guess fell through to a non-safetensors file (also seen with ROCm fallback paths).

Common situations: Old diffusers LoRAs shipped as pytorch_lora_weights.bin; checkpoints from civitai in .ckpt format; ROCm envs where safetensors guess fails and a .bin is chosen.

Related errors

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/01e2c24edcef0a43. Report an issue: GitHub.

Appendix: source

Thrown at python/sglang/multimodal_gen/runtime/utils/hf_diffusers_utils.py:653

        if weight_name is not None:
            target = os.path.join(local_path, weight_name)
            if not os.path.isfile(target):
                raise FileNotFoundError(
                    f"Specified lora_weight_name '{weight_name}' not found in "
                    f"{local_path}"
                )
            return target
        guessed = _best_guess_weight_name(local_path, file_extension=".safetensors")
        if guessed is None and current_platform.is_rocm():
            guessed = _best_guess_weight_name(
                model_name_or_path, file_extension=".safetensors"
            )
        return os.path.join(local_path, guessed)

    resolved_weight = resolve_weight(model_name_or_path, weight_name=weight_name)
    selected_file = resolved_weight.selected_file
    if not selected_file.endswith(".safetensors"):
        raise ValueError(
            "Native diffusion LoRA loading requires a safetensors file, got "
            f"{selected_file!r}"
        )

    source = resolved_weight.inventory.source
    if source.kind == "local":
        assert source.local_path is not None
        if os.path.isfile(source.local_path):
            return source.local_path
        return os.path.join(source.local_path, selected_file)

    assert source.repo_id is not None
    allow_patterns = ["*.json", selected_file]
    selected_parent = os.path.dirname(selected_file)
    if selected_parent:
        allow_patterns.insert(1, f"{selected_parent}/*.json")
    local_path = maybe_download_model(
        source.repo_id,

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