What is ZK Rollup (zkEVM)?

ZK Rollup with zkEVM is a Layer 2 scaling solution that executes transactions off-chain and generates zero-knowledge proofs (typically SNARKs or PLONKs) to cryptographically verify the correctness of state transitions on Layer 1. The "zkEVM" designation indicates that the rollup supports Ethereum Virtual Machine compatibility, allowing existing Solidity smart contracts to be deployed with minimal or no modifications. The system works by having a sequencer batch transactions, execute them off-chain, and then generate a validity proof that mathematically demonstrates all transactions were executed correctly. This proof, along with compressed state data, is submitted to a verifier contract on Ethereum L1. Unlike optimistic rollups, there is no challenge period — once the proof is verified on-chain, the state transition is immediately final.

ZK Rollups with zkEVM provide strong security guarantees inherited from Ethereum L1, as the validity proofs are mathematically unforgeable — an invalid state transition cannot produce a valid proof. This eliminates the need for a 7-day challenge period, enabling faster withdrawals to L1 compared to optimistic rollups. The main technical challenge is the computational cost of generating zero-knowledge proofs for EVM-compatible execution, as the EVM was not designed with zero-knowledge proof generation in mind. Different projects take different approaches to this: some implement a fully equivalent EVM (type 1 or type 2 zkEVM), while others make modifications for proof-generation efficiency (type 3 or type 4). Proof generation requires significant computational resources but is performed off-chain, so it does not affect user-facing transaction costs directly.

Several major projects implement ZK Rollup with zkEVM technology. Polygon zkEVM (now part of the Polygon AggLayer) launched its mainnet in March 2023 as a type 2 zkEVM. zkSync Era, developed by Matter Labs, launched in March 2023 with a custom LLVM-based compilation approach. Scroll launched its zkEVM mainnet in October 2023, focusing on EVM equivalence. Linea, developed by Consensys, also operates as a zkEVM rollup. These projects collectively represent one of the most active areas of blockchain research and development, with the long-term goal of making zero-knowledge proofs efficient enough that zkEVM rollups become the primary scaling solution for Ethereum.