Glossary · Term

Hydra effect

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Definition

Plain language

When you switch off one part of a neural network and another part quietly takes over its job, so the behavior survives anyway.

As stated in the literature

An interpretability phenomenon in which ablating a component is compensated for by redundant components, so single-component ablations underestimate a behavior's distributed implementation; invoked to explain why head-zeroing fails to remove behaviors at larger model scale.

Why it matters: It warns that switching off a single component can underestimate how a behavior is really implemented, since the model spreads the work across redundant parts.

For example, you disable the network part you think controls a behavior, but the behavior keeps happening because a backup part quietly picks up the slack.

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