Rollup
An L2 architecture that batches transactions off-chain and posts compressed state + proofs back to L1 for settlement.
Two dominant flavours: Optimistic rollup (fraud proofs, 7-day windows) and ZK rollup (zero-knowledge rollup) (validity proofs, fast finality). Rollups inherit L1 security; differences in proof systems, sequencer decentralisation, and data availability drive risk.
Related terms
- Optimistic rollupAn L2 that posts state roots to L1 and assumes them valid unless a fraud proof is submitted within a challenge window.
- ZK rollup (zero-knowledge rollup)An L2 that posts validity proofs to L1, enabling near-instant withdrawals and stronger trust assumptions than optimistic rollups.
- L2 (Layer-2)A scaling network that inherits security from an L1 by posting state roots back — rollups, validiums, plasma.
- SequencerThe entity that orders transactions on a rollup — typically centralised today, with decentralisation roadmaps in progress.