Optimistic Rollups Explained: Fraud Proofs, Sequencers and Exits
Transactions are accepted optimistically and can be challenged under the rollup’s proof rules.
A sequencer confirmation is useful for UX but not identical to Ethereum-finalized withdrawal security.
Key takeaways
Execution happens on L2. Batches and commitments are posted to Ethereum.
Fraud proofs enforce correctness. At least one capable challenger must be able to act.
Canonical exits can be delayed. Challenge periods protect settlement.
Admin keys can dominate early systems. Upgrade and pause powers require inspection.
The security path
Users transact through a sequencer, nodes reproduce L2 state and commitments reach Ethereum. If an invalid state root is proposed, the dispute mechanism should reject it before final withdrawal.
Bridges change the model
Third-party liquidity bridges can offer fast exit by advancing funds, adding counterparty, smart-contract and liquidity risk beyond the canonical rollup.
What to compare
Review proof maturity, data availability, sequencer failure mode, forced inclusion, upgrade delay and the exact assets supported by the canonical bridge.
Decision checklist
Verify current official documentation, contracts or legal entities, administrator permissions, fees, liquidity and the full exit path. Test the smallest practical transaction and record what happens when an interface, oracle, bridge, operator or counterparty fails.
Keep a dated baseline of addresses, reserves or collateral, governance roles and normal withdrawal results. Recheck it after upgrades or incidents. An audit, license application, partnership or TVL number answers only one part of the risk.
Before increasing exposure, define an observable stop condition: a collateral deviation, missed withdrawal, governance change, loss of market depth or unsupported software version. Decide the response in advance and retain enough native gas and independent wallet access to execute it without relying on customer support.