What do --lowvram, --highvram, --novram and the dynamic VRAM switches mean in ComfyUI v0.42.5, and when does --lowvram do nothing?

Problem. Older tutorials describe --lowvram as splitting the UNet; in current builds its meaning depends on DynamicVRAM. Conditions. ComfyUI v0.42.5, NVIDIA or recent AMD ROCm GPU. Method. comfy/cli_args.py: enables_dynamic_vram() is true unless --disable-dynamic-vram, --highvram, --gpu-only, --novram or --cpu is given (--enable-dynamic-vram forces it). main.py enables it only when the GPU is NVIDIA, or AMD with ROCm 7.14 or newer, torch is 2.8+ (2.12+ recommended in the log text) and a working comfy-aimdo is installed; otherwise it logs a warning and falls back to the legacy ModelPatcher. The --lowvram help text states it does nothing when dynamic VRAM is enabled, and otherwise only makes text encoders run on the CPU. Related knobs: --reserve-vram GB, --vram-headroom GB (DynamicVRAM extra headroom), --disable-smart-memory (aggressive offload to RAM), --async-offload, --fast-disk, --cache-ram for RAM thresholds. The vram flags are one mutually exclusive group. Failure modes. Copying old --lowvram advice and seeing no effect; Apple/Intel/CPU paths and torch < 2.8 take the legacy path with 'VRAM estimates may be unreliable'. Limitations. Behaviour read from flags and startup code; no GPU run. Help strings may change between releases. Version and date. v0.42.5. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Read from source; hardware behaviour not measured. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/483dae4326356b81de05d27aca3f433dd323cc25/comfy/cli_args.py",
      "note": "--lowvram help; enables_dynamic_vram; dynamic_vram_supported / startup"
    },
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/483dae4326356b81de05d27aca3f433dd323cc25/main.py",
      "note": "--lowvram help; enables_dynamic_vram; dynamic_vram_supported / startup"
    }
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}