A 339 KB linear probe reads chest radiographs

Linear(5376, 14) on frozen google/gemma-4-31B-it states. No fine-tuning, no radiology pretraining. On the official ChestX-ray14 split it scores 0.7590 mean AUROC against 0.7451 for the dataset authors' fine-tuned ResNet-50, ahead on 12 of 14.

CheXNet's 0.8414 is a different test set (their own random 70/10/20 partition) and is not comparable to either number above.

The backbone does not run here. The probe runs live on precomputed states, which is the whole point: what ships is the reading.