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📊 Evaluation & ML Foundations
Core

Catastrophic Forgetting

When you fine-tune a model on new data, gradient updates overwrite the weights that encoded old skills, so the model gets better at the narrow new task and quietly worse at things it used to do well. It bites in practice when a model fine-tuned on a customer task loses general instruction-following. The fixes are replay data, parameter-efficient methods like LoRA, lower learning rates, regularizing toward the base, and always evaluating on a held-out general set before and after.

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