What is transfer learning, and how do you decide whether to freeze, fine-tune, or use feature extraction?

Transfer learning is why you rarely train from scratch, and the real question is how much of the pretrained model to reuse versus adapt. The signal is a crisp decision grid over data size and task similarity, plus knowing when a low LR saves you from catastrophic forgetting.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.