Unlearning study: pre-trained knowledge can't be forgotten without collateral damage

_vztu · x · 2026-10-17

A research thread on LLM unlearning argues that most benchmarks inject fake identities via fine-tuning before unlearning, but such knowledge collapses within one epoch—real pre-trained knowledge fades far more slowly, as shown on LLaVA-1.5 and Qwen3-VL. The authors formalize the asymmetry: for fine-tuned knowledge a zero-cost fix always exists (revert to original weights), while under their assumptions any successful forgetting of pre-trained knowledge carries a strictly positive cost on the knowledge you want to keep.

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