torch.distributed is unsupported on Windows ROCm, so real torchao cannot import and Studio import-stubs it; the stub's config classes return None, so TorchAoConfig(quant_type=None) crashed exports with 'quant_type must be either a string or an AOBaseConfig instance, got NoneType'.
Gate the portable torchao FP8/INT8 path off on Windows ROCm via a shared is_win32_rocm() helper (used by both the import stub and the export gate so they can't drift), and add an early defensive error in export_merged_model so a forced torchao request fails fast with a clear message instead of the cryptic crash. The Export UI also hides torchao and stops claiming it works there.
No change on Linux, macOS, or Windows CUDA (torchao is real); Windows ROCm users keep 16-bit merged and GGUF quantization.
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