Inactivity leak

Ethereum needs validators holding two-thirds of the stake to vote for finality. If more than a third disappear, for example because of a widespread client bug or a network split, finality stalls. After four epochs without finality the protocol enters the inactivity leak: validators that are not attesting see their balances shrink, and the penalty grows the longer the situation lasts.

As offline validators lose stake, the share held by active ones rises until it again exceeds two-thirds, and the chain can finalise. The design guarantees that Ethereum recovers on its own from a mass outage without any manual intervention, and that in a network partition each side would eventually finalise its own version, making the split visible rather than silent.

The leak is not slashing: it punishes absence, not malicious signatures, and validators that stay online during the event lose little or nothing. It is also the main argument for client diversity, since a bug in a client run by a large share of validators could trigger heavy leak losses for all of its users at once.