What is Rollup?

A rollup is a Layer 2 scaling solution that processes transactions off the Ethereum mainnet but posts transaction data or proofs back to Layer 1, inheriting Ethereum’s security while offering dramatically higher throughput and lower fees. Rollups have become the dominant scaling strategy for Ethereum and now handle more daily transactions than the Ethereum mainnet itself.

The core idea is simple: instead of every Ethereum validator processing every transaction, rollups batch hundreds or thousands of transactions together, execute them off-chain on their own network, and then submit a compressed summary to Ethereum. This division of labor means users get fast, cheap transactions while Ethereum serves as the settlement and data availability layer.

Two types of rollups exist, differing in how they prove transaction validity to Ethereum.

Optimistic rollups assume transactions are valid by default and only run computation if someone submits a fraud proof challenging a batch. This “innocent until proven guilty” approach is simpler to implement and offers full EVM compatibility. Leading optimistic rollups include Arbitrum (the largest L2 by TVL), Base (built by Coinbase), and Optimism (whose OP Stack powers an ecosystem of chains). The tradeoff is a 7-day challenge period for withdrawals back to Ethereum, though bridge services offer faster exits for a fee.

ZK (zero-knowledge) rollups use cryptographic proofs to mathematically verify that every transaction in a batch is valid before posting to Ethereum. This provides instant finality — no challenge period required — and potentially stronger security guarantees. Leading ZK rollups include zkSync, StarkNet, Scroll, Linea, and Polygon zkEVM. The tradeoff is greater computational complexity in generating proofs, though rapid improvements in proving technology are narrowing this gap.

Ethereum’s Dencun upgrade (March 2024) introduced “blob” transactions (EIP-4844), a dedicated data format for rollups that reduced their data posting costs by 90-99%. This made transactions on rollups like Base and Arbitrum cost fractions of a cent, comparable to centralized platforms.

The rollup ecosystem has expanded into a multi-chain landscape. The OP Stack (Optimism’s open-source rollup framework) powers Base, Zora, Mode, and dozens of other chains. Arbitrum Orbit enables custom rollup deployments. This “rollup-centric roadmap” is Ethereum’s official scaling strategy, with the Ethereum Foundation envisioning a future of thousands of interconnected rollups rather than a single monolithic chain.

Last updated: April 2026