What it means
Two broad approaches
Optimistic rollups use a mechanism for challenging invalid state claims. Validity rollups submit proofs for state transitions. Both categories contain implementations with different operating and security assumptions.
Beyond transaction speed
A sequencer receipt, a posted batch, a proof or challenge outcome, and a completed withdrawal are separate milestones. Data availability, upgrade controls, bridge design and failure recovery affect the risk of a particular rollup. A general label cannot substitute for the deployment’s current documentation.
Related concepts
In practice
A concrete example
A checkout may show a quick L2 confirmation while a later transfer to Layer 1 follows a separate bridge and settlement process.
Technical notes & boundaries
Do not assign one withdrawal delay, fee model or finality time to every rollup. Validity proofs do not remove all contract or operational risks.
Go to the source.
Original references used for this definition. Product details and standards can change.