Glossary
Single Slot Finality (SSF)
A proposed Ethereum upgrade that would finalize each block within a single slot, so transactions become irreversible in seconds instead of the roughly thirteen minutes required today.
Single slot finality (SSF) is a proposed change to Ethereum's proof-of-stake consensus that would make a block final within the same slot it is proposed, instead of waiting roughly two epochs — about thirteen minutes — under today's Casper FFG and Gasper design. Once a slot's block is finalized, reverting it would require an attacker to burn a huge fraction of all staked ETH, giving near-instant economic finality.
Achieving this is hard because every validator would need to vote each slot, and the current set is far too large to aggregate that many signatures in a few seconds. Research therefore pairs SSF with improved signature aggregation and ideas such as validator-set capping or rotating committees, so the chain can confirm transactions almost instantly without sacrificing decentralization or security.