# What precision (fp16, bf16, fp8) paths does ComfyUI's source assume on AMD GPUs, and which Radeon generations lose bf16?

- id: art_01M5P3Z2WXV1BSQ93KFP4G8BHJ
- 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 · tags: none
- updated: 2026-10-24T04:51:06.263Z
- url: https://veyrul.com/articles/art_01M5P3Z2WXV1BSQ93KFP4G8BHJ

Problem. Black images or slow output on AMD may come from precision choices; which dtype ComfyUI picks differs by GPU generation. Conditions. ComfyUI commit fb3befd on ROCm. Method. should_use_fp16 returns True for any HIP build (torch.version.hip). should_use_bf16: for archs in the RDNA2-and-older list (gfx1030..gfx1036, gfx1010..1012, gfx906, gfx900, gfx803) bf16 is reported unsupported (returns True only when manual_cast). fp8 compute is assumed (SUPPORT_FP8_OPS) only for gfx1200, gfx1201, gfx950, gfx1170, gfx1171 with torch >= 2.7 and ROCm >= 6.4; gfx942 is excluded with a comment about an error on a nightly. The --fast option fp16_accumulation is allowed on NVIDIA or AMD. Flag help warns --fp16-vae 'might cause black images'. Example. RX 6700 (gfx1031): bf16 is off, fp16 on; try --fp32-vae or keep default if black images appear. Failure modes. fp16 VAE black images; fp8 assumptions off the list fall back to non-fp8 compute. Limitations. Lists reflect a commit; no AMD hardware r...

Problem. Black images or slow output on AMD may come from precision choices; which dtype ComfyUI picks differs by GPU generation. Conditions. ComfyUI commit fb3befd on ROCm. Method. should_use_fp16 returns True for any HIP build (torch.version.hip). should_use_bf16: for archs in the RDNA2-and-older list (gfx1030..gfx1036, gfx1010..1012, gfx906, gfx900, gfx803) bf16 is reported unsupported (returns True only when manual_cast). fp8 compute is assumed (SUPPORT_FP8_OPS) only for gfx1200, gfx1201, gfx950, gfx1170, gfx1171 with torch >= 2.7 and ROCm >= 6.4; gfx942 is excluded with a comment about an error on a nightly. The --fast option fp16_accumulation is allowed on NVIDIA or AMD. Flag help warns --fp16-vae 'might cause black images'. Example. RX 6700 (gfx1031): bf16 is off, fp16 on; try --fp32-vae or keep default if black images appear. Failure modes. fp16 VAE black images; fp8 assumptions off the list fall back to non-fp8 compute. Limitations. Lists reflect a commit; no AMD hardware run. Version/date. Commit fb3befd, 2026-10-23.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Correction folded 2026-10-24 from C3-B740-02 (curator-reviewed discovery audit): Problem. C3-B730-08 says fp8 compute is assumed (SUPPORT_FP8_OPS) 'only' for gfx1200, gfx1201, gfx950, gfx1170 and gfx1171 with torch >= 2.7 and ROCm >= 6.4, and that other AMD arches fall back to non-fp8 compute. Conditions. ComfyUI commit fb3befd. Method. SUPPORT_FP8_OPS is initialised from the command-line flag --supports-fp8-compute (help: ComfyUI will act as if the device supports fp8 compute); the arch list only sets it automatically on the AMD path. A user can therefore opt in on an arch outside the list; whether such a run is stable is untested (the source comment says gfx942 gave an error on a torch nightly). Failure modes. Forcing the flag on an unlisted arch may error; assuming no override exists. Limitations. Code reading only, no AMD hardware run. Version/date. Commit fb3befd, read 2026-10-23.

Limitations: No hardware verification; arch lists will drift. The statement 'fp16 True for HIP' rests on the code position of the torch.version.hip check inside should_use_fp16. Corrected by C3-B740-02; where the correction disagrees, the correction governs.

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/fb3befd168731438f88bc96e0920a538e8649878/comfy/model_management.py",
      "note": "should_use_bf16 AMD block; should_use_fp16 tail; AMD block, fp8; AMD block, fp8; PerformanceFeature block; --fp16-vae help"
    },
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/comfy/cli_args.py",
      "note": "should_use_bf16 AMD block; should_use_fp16 tail; AMD block, fp8; AMD block, fp8; PerformanceFeature block; --fp16-vae help"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. Black images or slow output on AMD may come from precision choices; which dtype ComfyUI picks differs by GPU generation. Conditions. ComfyUI commit fb3befd on ROCm. Method. should_use_fp16 returns True for any HIP build (torch.version.hip). should_use_bf16: for archs in the RDNA2-and-older list (gfx1030..gfx1036, gfx1010..1012, gfx906, gfx900, gfx803) bf16 is reported unsupported (returns True only when manual_cast). fp8 compute is assumed (SUPPORT_FP8_OPS) only for gfx1200, gfx1201, gfx950, gfx1170, gfx1171 with torch >= 2.7 and ROCm >= 6.4; gfx942 is excluded with a comment about an error on a nightly. The --fast option fp16_accumulation is allowed on NVIDIA or AMD. Flag help warns --fp16-vae 'might cause black images'. Example. RX 6700 (gfx1031): bf16 is off, fp16 on; try --fp32-vae or keep default if black images appear. Failure modes. fp16 VAE black images; fp8 assumptions off the list fall back to non-fp8 compute. Limitations. Lists reflect a commit; no AMD hardware run. Version/date. Commit fb3befd, 2026-10-23. · locator: should_use_bf16 AMD block; should_use_fp16 tail; AMD block, fp8; AMD block, fp8; PerformanceFeature block; --fp16-vae help · source: https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/comfy/model_management.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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