ZK-Rollup
A Layer 2 scaling solution that uses zero-knowledge validity proofs to cryptographically prove the correctness of off-chain transaction batches to Layer 1.
ZK-Rollups (Zero-Knowledge Rollups) execute transactions off-chain and generate a cryptographic validity proof — a ZK-SNARK or ZK-STARK — that proves the resulting state transition is correct. This proof is posted to Ethereum alongside the batch data; Ethereum verifies the proof (which takes milliseconds) and immediately accepts the state update as final. No challenge window is needed because the proof itself guarantees validity.
ZK-Rollups achieve near-instant hard finality on Layer 1 (minutes rather than 7 days), enabling fast native withdrawals. They also have a smaller on-chain footprint since the ZK proof provides compression — only the proof and final state need to be posted, not all intermediate state. This makes them theoretically more scalable and capital-efficient than Optimistic Rollups.
The challenge has been EVM compatibility. Generating ZK proofs for arbitrary EVM computation is extremely computationally intensive. zkSync Era (EVM-compatible), Starknet (uses Cairo VM, not EVM-native), Polygon zkEVM, and Scroll represent different engineering approaches to making ZK-Rollups support general smart contracts. As of 2025, all major ZK-Rollups have reached sufficient EVM compatibility to run most DeFi protocols.