Rollups

Rollups are a category of Layer 2 blockchain scalability solutions that execute transactions off the main chain (Layer 1) and post data or cryptographic proofs back to Layer 1 to inherit its security. They aim to increase transaction throughput and reduce costs while preserving the security model of the underlying blockchain.

There are two main families: optimistic rollups and zero-knowledge rollups (zk-rollups). Optimistic rollups assume transactions are valid by default and use fraud proofs to challenge incorrect state transitions; a dispute window allows anyone to submit a proof, after which the batch is finalized. ZK-rollups generate a validity proof for each batch, posting a succinct cryptographic proof along with a compressed state update; the on-chain verifier checks the proof, enabling faster finality.

Mechanically, a rollup operator collects user transactions, executes them off-chain, and posts a compact recap to Layer 1. Data availability is typically ensured by publishing calldata or proofs on Layer 1, enabling any party to reconstruct the state. Security is anchored to Layer 1; misbehavior can be contested on-chain through proofs or verification.

Use cases include decentralized exchanges, payments, and general smart contract execution at lower fees and higher throughput. Withdrawal and finality timing can vary: optimistic rollups incur a challenge period, while zk-rollups generally offer quicker finality once proofs are verified.

Notable implementations include optimistic rollups such as Optimism and Arbitrum, and zk-rollups such as zkSync, StarkWare, and Polygon zkEVM. Rollups represent one approach among Layer 2 strategies to scale blockchains while maintaining strong security guarantees.