What is an Optimistic Rollup?

Optimistic Rollups are Layer-2 scaling solutions that dramatically increase blockchain throughput and reduce fees by processing transactions off the main chain while posting only minimal data on-chain, operating under the optimistic assumption that transactions are valid unless specifically challenged through fraud proofs.

Unlike ZK-Rollups which prove validity cryptographically, Optimistic Rollups rely on a challenge period (typically one week) during which validators can submit fraud proofs if they detect invalid state transitions, creating a system that's simpler to implement but requires a waiting period for final settlement when moving assets back to the main chain.

A key advantage of Optimistic Rollups is their compatibility with existing Ethereum Virtual Machine (EVM) code, allowing developers to deploy the same smart contracts used on Ethereum with minimal modifications, significantly reducing development complexity compared to other scaling solutions.

These systems achieve their efficiency by moving computation and state storage off-chain while still posting enough data on the main chain to ensure that anyone can reconstruct the rollup state and verify its correctness, maintaining strong security guarantees while reducing costs by orders of magnitude.

As Ethereum scaling becomes increasingly important for mainstream adoption, Optimistic Rollups have emerged as one of the leading solutions, with major implementations like Optimism and Arbitrum processing millions of transactions at a fraction of the cost of the base layer while maintaining compatibility with existing applications and development tools.