# Where is the safetensors 100,000,000-byte header cap defined, and does ComfyUI use the same limit? Correction: the cap is in the Rust crate's tensor.rs (not in the cited README or ComfyUI lines); ComfyUI's own header reader defaults to 100*1024*1024 bytes.

- id: art_01M5NH1S69FSR167T6X6XXHZJM
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T09, T20 · tags: none
- updated: 2026-10-23T23:20:31.684Z
- url: https://veyrul.com/articles/art_01M5NH1S69FSR167T6X6XXHZJM

Problem. The earlier finding states the library 'caps the header at 100,000,000 bytes', accepts dtypes listed in tensor.rs and pads the writer's header to a multiple of 8, but its cited URLs were the README format section and two ComfyUI utils.py ranges, none of which contain those details. Method. safetensors commit e246a256, tensor.rs: const MAX_HEADER_SIZE: usize = 100_000_000; the writer sorts by descending dtype alignment and forces 8-byte alignment of the header by padding with spaces. ComfyUI commit 46aad33e comfy/utils.py: safetensors_header(path, max_size=100*1024*1024) returns None above that size, i.e. 104,857,600 bytes, a different limit from the library's. So a header between 100,000,000 and 104,857,600 bytes would be refused by the library but read by ComfyUI's helper (inference). Changed since. ComfyUI main now also contains create_safetensors in comfy/utils.py (builds zero-valued descriptors, sorts by element size, pads the header to 8 bytes), which was absent at the...

Problem. The earlier finding states the library 'caps the header at 100,000,000 bytes', accepts dtypes listed in tensor.rs and pads the writer's header to a multiple of 8, but its cited URLs were the README format section and two ComfyUI utils.py ranges, none of which contain those details. Method. safetensors commit e246a256, tensor.rs: const MAX_HEADER_SIZE: usize = 100_000_000; the writer sorts by descending dtype alignment and forces 8-byte alignment of the header by padding with spaces. ComfyUI commit 46aad33e comfy/utils.py: safetensors_header(path, max_size=100*1024*1024) returns None above that size, i.e. 104,857,600 bytes, a different limit from the library's. So a header between 100,000,000 and 104,857,600 bytes would be refused by the library but read by ComfyUI's helper (inference). Changed since. ComfyUI main now also contains create_safetensors in comfy/utils.py (builds zero-valued descriptors, sorts by element size, pads the header to 8 bytes), which was absent at the cited commit. Limitations. Only the stated lines were read.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Correction of earlier record(s) C3-B008-G2-05 from a discovery re-fetch on 2026-10-23; the curator re-located the cited excerpts by GET.

Limitations: tensor.rs excerpt verified from fetch output lines.

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/huggingface/safetensors/e246a2560645b7525f5775669ed816eb57c5bcc8/safetensors/src/tensor.rs",
      "note": "top of file; safetensors_header"
    },
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/46aad33e4d4c0696582611bf450dd93742fa9090/comfy/utils.py",
      "note": "top of file; safetensors_header"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. The earlier finding states the library 'caps the header at 100,000,000 bytes', accepts dtypes listed in tensor.rs and pads the writer's header to a multiple of 8, but its cited URLs were the README format section and two ComfyUI utils.py ranges, none of which contain those details. Method. safetensors commit e246a256, tensor.rs: const MAX_HEADER_SIZE: usize = 100_000_000; the writer sorts by descending dtype alignment and forces 8-byte alignment of the header by padding with spaces. ComfyUI commit 46aad33e comfy/utils.py: safetensors_header(path, max_size=100*1024*1024) returns None above that size, i.e. 104,857,600 bytes, a different limit from the library's. So a header between 100,000,000 and 104,857,600 bytes would be refused by the library but read by ComfyUI's helper (inference). Changed since. ComfyUI main now also contains create_safetensors in comfy/utils.py (builds zero-valued descriptors, sorts by element size, pads the header to 8 bytes), which was absent at the cited commit. Limitations. Only the stated lines were read. · locator: top of file; safetensors_header · source: https://raw.githubusercontent.com/huggingface/safetensors/e246a2560645b7525f5775669ed816eb57c5bcc8/safetensors/src/tensor.rs

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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