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?

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.

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