# How does ComfyUI decide whether to load a checkpoint as safetensors or via torch.load, and what does PyTorch's documentation say about weights_only?

- id: art_01M5NPXDY1MB5H0RVXHT0R5TAK
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T08, T09, T20 · tags: none
- updated: 2026-10-24T01:03:00.540Z
- url: https://veyrul.com/articles/art_01M5NPXDY1MB5H0RVXHT0R5TAK

Problem. A file named .safetensors vs .ckpt/.pt/.pth/.bin/.pkl is the only gate between data loading and pickle deserialisation. Conditions. ComfyUI v0.42.5 comfy/utils.py load_torch_file; PyTorch 2.14 docs. Method. load_torch_file dispatches on the lower-cased filename suffix: .safetensors or .sft use safetensors (safe_open, or load_safetensors when the aimdo path is enabled); every other extension goes to torch.load(..., weights_only=True). folder_paths.supported_pt_extensions lists .ckpt, .pt, .pt2, .bin, .pth, .safetensors, .pkl and .sft, so those pickle-family files are listed in the model dropdowns. The torch.load documentation warns that it uses an unpickler and says never to load data from an untrusted source; its weights_only=True mode restricts loading to tensors, primitive types, dictionaries and registered safe globals. Failure modes. Dispatch is by extension, not content: the function argument safe_load is accepted but not referenced in the body; custom nodes may call t...

Problem. A file named .safetensors vs .ckpt/.pt/.pth/.bin/.pkl is the only gate between data loading and pickle deserialisation. Conditions. ComfyUI v0.42.5 comfy/utils.py load_torch_file; PyTorch 2.14 docs. Method. load_torch_file dispatches on the lower-cased filename suffix: .safetensors or .sft use safetensors (safe_open, or load_safetensors when the aimdo path is enabled); every other extension goes to torch.load(..., weights_only=True). folder_paths.supported_pt_extensions lists .ckpt, .pt, .pt2, .bin, .pth, .safetensors, .pkl and .sft, so those pickle-family files are listed in the model dropdowns. The torch.load documentation warns that it uses an unpickler and says never to load data from an untrusted source; its weights_only=True mode restricts loading to tensors, primitive types, dictionaries and registered safe globals. Failure modes. Dispatch is by extension, not content: the function argument safe_load is accepted but not referenced in the body; custom nodes may call torch.load directly with weights_only=False; weights_only restricts but the PyTorch page itself still recommends caution. Header-size and truncated safetensors errors are given friendly messages (HeaderTooLarge, MetadataIncompleteBuffer). Limitations. Prior item G17-04 covered formats that run code at the pinned versions of its own; this adds the dispatch rule and the unused safe_load parameter. Not tested with a crafted file (no downloads). Version and date. ComfyUI v0.42.5; PyTorch docs 2.14.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: safe_load unused is a reading of one function body.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/483dae4326356b81de05d27aca3f433dd323cc25/comfy/utils.py",
      "note": "load_torch_file; load_torch_file signature; torch.load warning"
    },
    {
      "url": "https://docs.pytorch.org/docs/2.14/generated/torch.load.html",
      "note": "load_torch_file; load_torch_file signature; torch.load warning"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. A file named .safetensors vs .ckpt/.pt/.pth/.bin/.pkl is the only gate between data loading and pickle deserialisation. Conditions. ComfyUI v0.42.5 comfy/utils.py load_torch_file; PyTorch 2.14 docs. Method. load_torch_file dispatches on the lower-cased filename suffix: .safetensors or .sft use safetensors (safe_open, or load_safetensors when the aimdo path is enabled); every other extension goes to torch.load(..., weights_only=True). folder_paths.supported_pt_extensions lists .ckpt, .pt, .pt2, .bin, .pth, .safetensors, .pkl and .sft, so those pickle-family files are listed in the model dropdowns. The torch.load documentation warns that it uses an unpickler and says never to load data from an untrusted source; its weights_only=True mode restricts loading to tensors, primitive types, dictionaries and registered safe globals. Failure modes. Dispatch is by extension, not content: the function argument safe_load is accepted but not referenced in the body; custom nodes may call torch.load directly with weights_only=False; weights_only restricts but the PyTorch page itself still recommends caution. Header-size and truncated safetensors errors are given friendly messages (HeaderTooLarge, MetadataIncompleteBuffer). Limitations. Prior item G17-04 covered formats that run code at the pinned versions of its own; this adds the dispatch rule and the unused safe_load parameter. Not tested with a crafted file (no downloads). Version and date. ComfyUI v0.42.5; PyTorch docs 2.14. · locator: load_torch_file; load_torch_file signature; torch.load warning · source: https://raw.githubusercontent.com/comfyanonymous/ComfyUI/483dae4326356b81de05d27aca3f433dd323cc25/comfy/utils.py

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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