Rollup
An L2 scaling technique that bundles hundreds of transactions into one on-chain batch, drastically reducing per-transaction costs.
Rollup — A rollup is a Layer 2 scaling solution that executes transactions off-chain, bundles them into batches, and posts compressed transaction data or validity proofs back to the Layer 1 blockchain. Rollups are the dominant scaling approach for Ethereum, collectively processing over 50 transactions per second and reducing gas costs by 10x to 100x compared to mainnet execution.
What Is a Rollup?
A rollup is a type of Layer 2 blockchain that "rolls up" many transactions into a single batch and submits it to the Layer 1 for data availability and verification. Instead of processing each transaction individually on the expensive base layer, rollups handle execution in their own environment and only publish the minimum data needed for the L1 to verify correctness.
The term "rollup" covers two distinct architectures: optimistic rollups and zero-knowledge (ZK) rollups. Both achieve significant cost savings but differ in how they prove transaction validity to the L1.
How Rollups Work
A rollup sequencer collects user transactions, orders them, executes them against the current state, and produces a batch. This batch contains compressed transaction data and a new state root. The batch is then posted to the Layer 1 as calldata or blob data (after Ethereum's Dencun upgrade).
Optimistic rollups assume batches are valid and allow a 7-day challenge window during which anyone can submit a fraud proof if they detect an invalid state transition. ZK rollups generate a cryptographic validity proof alongside each batch that the L1 smart contract verifies on-chain before accepting the state update.
Why Rollups Matter
Rollups are Ethereum's primary scaling roadmap. Vitalik Buterin has described Ethereum's future as "rollup-centric," meaning the base layer focuses on security and data availability while rollups handle execution. For DeFi users and token projects, rollups provide a practical path to affordable, fast transactions without sacrificing the security guarantees of Ethereum.
Related Terms
Optimistic Rollup
A rollup type (used by Optimism, Arbitrum) that assumes transactions are valid by default and only verifies them if challenged.
Read definition Blockchain & Crypto FundamentalsZK Rollup
A rollup type that uses zero-knowledge proofs to cryptographically verify transaction batches without requiring a challenge period.
Read definition Blockchain & Crypto FundamentalsLayer 2 (L2)
A scaling solution built on top of a Layer 1 blockchain to increase throughput and reduce costs while inheriting base layer security.
Read definition Blockchain & Crypto FundamentalsLayer 1 (L1)
A base blockchain network like Ethereum, Solana, or BNB Chain that handles all transaction settlement directly on-chain.
Read definition Blockchain & Crypto FundamentalsGas
The unit measuring the computational effort required to execute operations on EVM chains; gas fees are gas used × gas price.
Read definitionFrequently Asked Questions
Common questions about Rollup in cryptocurrency and DeFi.
A rollup posts transaction data back to the Layer 1 and inherits its security. A sidechain runs its own consensus and validators independently, meaning it does not benefit from the L1's security guarantees. Rollups are considered more secure because the L1 can verify their state transitions.
Some rollups have native tokens — Arbitrum has ARB and Optimism has OP, both used for governance. Others like Base and zkSync Era did not launch with tokens initially. Gas on most rollups is still paid in ETH.
After Ethereum's Dencun upgrade introduced blob data, rollup transaction fees dropped to $0.01 to $0.10 for simple transfers and $0.05 to $0.50 for DEX swaps. This represents a 50x to 100x cost reduction compared to equivalent mainnet transactions.
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