Network profile: Optimism (OP Mainnet)
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Network name
Optimism
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Token
ETH
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RPC
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Chain ID
10
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Block explorer
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Website
Formerly known as Optimism, OP Mainnet is a layer 2 (L2) rollup helping to scale Ethereum. Let's unpack how it works.
L2s are a type of blockchain closely linked to a corresponding layer 1 (L1), which, in this case, is Ethereum. Transactions are handled on the L2 itself, the execution layer, whilst data about these transactions is 'rolled up' into a condensed form and posted on L1, demanding significantly less computation than if all of the transactions were to be conducted entirely on L1. Their structure allows users access to high-capacity, fast and low-cost alternative to Ethereum mainnet whilst retaining the same fundamental mechanisms and features. Critically, L2s also inherit Ethereum's security and reliability. OP Mainnet's execution layer is called the OVM, or Optimism Virtual Machine.
OP Mainnet uses a system similar to Proof-of-Stake, in which entities running nodes help secure the network. In this case, they are called verifiers. Additionally, OP Mainnet requires a sequencer, responsible for collecting transactions from the L2, rolling them up, and posting them to L1 (Ethereum). The Optimism organization itself currently runs the sole sequencer on the network.
As its name not-so-subtly hints, OP Mainnet belongs to the optimistic rollup category. Similarly to Arbitrum, one of the other major L2 platforms, OP Mainnet's protocols assume that all transactions are valid. This approach means that the network does not have to compute every transaction, significantly reducing congestion; instead, computation is only performed when the validity of the block is challenged.
This occurs in a process referred to as a fraud proof, which is where verifiers come in: when the state information or 'commitment' (i.e. the bundle of rolled-up transactions) is posted to Ethereum, a one-week 'challenge window' begins. Verifiers check state information and are responsible for initiating a fraud proof to resolve the issue. If proven right, verifiers are rewarded and the proposed commitment is replaced with a new one. This 'How Optimism Works' page is a good explainer if you want to find out more.
Gas controls on OP Mainnet
When using OP Mainnet in MetaMask, you won't be able to manually adjust the amount of gas you pay using advanced gas controls, as you would on other networks. The feature is disabled instead. This is because it's not possible for users to specify gas limits when OP Mainnet submits the transaction to Ethereum. You can read more here.