Glossary
Sync Committee
A rotating group of 512 Ethereum validators that signs block headers each period so light clients can follow the chain by verifying just one aggregated signature.
A sync committee is a set of 512 validators, chosen at random from the active set, that serves for a fixed period of 256 epochs — roughly 27 hours — on Ethereum's proof-of-stake chain. During its term, each member signs the block header of every slot, and those signatures are aggregated into a single BLS signature attached to the block.
The purpose is to make life easy for light clients. Introduced in the Altair upgrade, the sync committee lets a resource-constrained device follow the chain's head by checking one aggregated signature per slot against a small, slowly changing committee, instead of tracking the full validator set. Members earn extra rewards for participating and are penalized for going offline, which keeps the mechanism reliable enough for wallets and bridges to trust.