hf download sudolink/sam3.1 checkpoints/sam3.1_multiplex_fp16.safetensors \
  --local-dir ~/comfyui/models
# flattens under models/checkpoints/ if HF nests the path

Or single file straight into checkpoints:

fish

hf download sudolink/sam3.1 checkpoints/sam3.1_multiplex_fp16.safetensors \
  --local-dir ~/comfyui/models/checkpoints
# if nested: mv ~/comfyui/models/checkpoints/checkpoints/*.safetensors ~/comfyui/models/checkpoints/

Used by

Comfy core SAM3_VideoTrack / SAM3_TrackToMask (text-prompt video track)
droz MiniMax H3 LatentMaskInpainting w Reference v3.1 (MaskVidExperiments)

Upstream packaging: Comfy-Org/sam3.1. License follows Meta SAM terms on the upstream card.