[Windows] RTX 5070 Ti (Blackwell) - cuInit error 100 fix guide

[loongmiaow-pixel]

Environment

• GPU: NVIDIA GeForce RTX 5070 Ti Laptop GPU (Blackwell, compute capability 12.0)
• Driver: 595.79 (CUDA 13.2)
• OS: Windows 11
• PyTorch: 2.11.0+cu130

Problem

After installing ComfyUI on an RTX 5070 Ti laptop, CUDA was not available:

• torch.cuda.is_available() returned False
• cuInit() returned error code 100
• nvidia-smi worked fine, but no CUDA program could access the GPU

Root Causes and Fixes

1. Windows GPU Preference: Hybrid graphics laptop routes Python to Intel iGPU by default. Fix: registry key GpuPreference=2 for python.exe
2. PATH DLL conflict: CUDA Toolkit cudart64_12.dll conflicts with PyTorch cu130 cudart64_13.dll. Fix: prioritize torch/lib in PATH
3. System-level CUDA_VISIBLE_DEVICES=-1: Must force-override to 0
4. Blackwell architecture: Needs TORCH_CUDA_ARCH_LIST=12.0

Full fix details and code available. RTX 5070 Ti/5080/5090 laptop users will hit this same issue.

Happy to contribute a PR with updated troubleshooting docs if helpful.