Glossary

Hard Fork

A change to a blockchain's rules that every node must adopt at the same block or time; nodes that do not upgrade are left on a separate chain. Ethereum ships its scheduled upgrades as hard forks after rehearsing them on testnets such as Sepolia and Hoodi; Glamsterdam's Hoodi activation, set for October 26, 2026, was pulled four days earlier over a gas-pricing issue.