Unlearning Isn't Deletion: Investigating Reversibility of Machine Unlearning in LLMs

In three linesStudy shows unlearning in LLMs merely suppresses information: minimal fine-tuning restores original behavior. Representation-level analysis framework (PCA, CKA, Fisher information) reveals four forgetting regimes by reversibility and catastrophicity. Identifies cases of seemingly irreversible targeted forgetting.

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