What is Rollup?
Last reviewed 2026-05-03
Entity coverage: 1 protocol, 0 tokens, 0 chains reference this concept.
First defined in: A Rollup-Centric Ethereum Roadmap (2020) by Vitalik Buterin
Cite / Read deeper: DeFi Intel modular blockchains deep-dive
A rollup batches transactions, executes them off the L1, and posts compressed data plus a proof (validity for ZK, fault-disputable for optimistic) back to the L1. Inherits L1 security plus its own throughput.
How it works
Users send transactions to the rollup's sequencer, which orders and executes them against the rollup's own state and returns near-instant pre-confirmations. Periodically the sequencer compresses a batch of these transactions and posts the data to the L1 — as calldata or, on Ethereum since EIP-4844, cheaper blob space — along with the new state root claimed to result from executing them.
What happens next depends on the proof system. An optimistic rollup assumes the posted root is correct but opens a challenge window (typically about seven days) during which anyone re-executing the batch can submit a fault proof; a successful challenge reverts the bad root and slashes the poster's bond. A ZK rollup instead submits a validity proof with each batch, which an L1 verifier contract checks before accepting the state root — no waiting period needed.
Because full transaction data lives on the L1, anyone can reconstruct the rollup's state independently, and users can bypass a censoring sequencer by forcing transactions in through the L1 bridge contract. Withdrawals exit through that same bridge once the relevant proof or challenge window finalizes.
Why it matters
Rollups are Ethereum's dominant scaling strategy: 10-100x throughput gain, 90-99% fee reduction post-EIP-4844, while inheriting L1 security.
Real-world examples
Arbitrum, Optimism, Base (optimistic); zkSync Era, Starknet, Linea, Scroll (ZK).
Related terms
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ZK Rollups deep-dive Browse GlossaryFrequently asked questions
What is a rollup in crypto?
A rollup batches transactions, executes them off the L1, and posts compressed data plus a proof (validity for ZK, fault-disputable for optimistic) back to the L1, inheriting L1 security plus its own throughput.
How does an optimistic rollup differ from a ZK rollup?
An optimistic rollup assumes the posted root is correct but opens a challenge window (typically about seven days) for fault proofs, while a ZK rollup submits a validity proof with each batch that an L1 verifier contract checks before accepting the state root, with no waiting period.
What are real-world examples of rollups?
Real-world examples include Arbitrum, Optimism, and Base (optimistic), as well as zkSync Era, Starknet, Linea, and Scroll (ZK).