ZK Rollups

ZK rollups take the opposite approach from optimistic rollups: every batch must include a cryptographic validity proof before Ethereum accepts it. zkSync, Starknet, and Scroll use variants of this model. There is no challenge window because invalid batches simply cannot be verified.

Validity proofs are computationally intensive. Provers must crunch through every transaction in a batch and produce a succinct proof that the new state root is correct. As prover hardware improves and zkEVM implementations mature, this cost is falling steadily.

For users, the practical difference is withdrawal speed and trust model. ZK exits can finalize in hours rather than days, and there is no need to hope someone is watching for fraud — math replaces the watcher.