Optimism refers to a broader ecosystem than a single blockchain. OP Mainnet is a network on which applications deploy contracts, while the OP Stack supplies software components that operators use to run compatible chains. A chain operator and an application developer therefore make different choices: the operator configures chain infrastructure, while the developer chooses a destination chain and its contract addresses. A familiar account address can exist on several such networks without carrying the same token balances between them.

The sequencer provides an early execution result, and the batcher compresses transaction data for publication to Ethereum. Nodes derive the chain from the published inputs and execute its rules. Documentation distinguishes unsafe blocks that have not yet been anchored through published data, safe blocks derived from L1 data, and finalized blocks whose L1 reference has finalized. These labels describe increasing settlement confidence. They are separate from the steps needed to prove and finalize a withdrawal through the canonical bridge.

An optimistic system permits state proposals before a separate validity proof accompanies every batch. The OP Stack fault-proof system allows participants to challenge a proposal through a dispute game. Its security documentation also describes safeguards and privileged roles that can pause bridge activity or reject faulty games. Consequently, assessing a particular chain requires both its proof rules and its deployed administrative configuration.

The fact that two chains use the OP Stack does not establish identical upgrade authority, data availability, or withdrawal behavior for every deployment.