Optimism, also called OP Mainnet, is a layer 2 network on Ethereum and the chain where the OP Stack began. This article explains who is behind it, how the rollup and its fees work, what the OP token does, and how to follow it live.
If you are new to layer 2, start with layer 1, layer 2 and layer 3.
What Optimism is and who built it
Optimism was created by a team that became OP Labs, and the main network launched in 2021. It is run within the Optimism Collective, a community structure that includes a non-profit Optimism Foundation, token-based governance, and a stated goal of funding public goods. OP Labs is a company that builds the software. These roles are separate, and the exact structure changes over time, so check Optimism's own documentation for the current state.
The problem it set out to solve is the same as other rollups: Ethereum is secure but expensive at busy times. Optimism lets users run EVM transactions at a much lower cost, while keeping data on Ethereum. Typical uses are decentralized finance, stablecoin transfers, apps and games.
The OP Stack and the Superchain
Optimism's software is open source and modular. It is called the OP Stack. Other chains, including Base, use it too. The Superchain is the idea of many OP Stack chains that share the same base software and standards, and work toward being able to talk to each other more easily. OP Mainnet is the original and best-known of them.
How it works: an optimistic rollup
OP Mainnet is an optimistic rollup. A sequencer receives transactions, orders them and produces a block every 2 seconds. It then posts compressed transaction data to Ethereum, so anyone can rebuild the chain from Ethereum. "Optimistic" means the results are accepted unless someone shows they are wrong.
The sequencer is run by a single operator today. This gives fast confirmations but is a point of centralization. Users can force their transactions through Ethereum if the sequencer is unavailable or refuses them, though it is slower. See rollups: optimistic vs zk.
Fault proofs
For withdrawals to Ethereum to be safe, the chain needs a way to check claims about its state. Optimism uses fault proofs: someone proposes a state, and during a challenge period anyone can dispute it, with the dispute settled by running the contested step on Ethereum. The system has been upgraded over time, and details of how permissionless it is have changed. For the current status, read Optimism's documentation.
Finality
A transaction is included within about 2 seconds. It is considered safe when its data is on Ethereum and final when that Ethereum block is finalized. A withdrawal through the standard bridge waits about seven days for the challenge period. See finality and confirmations.
Fees
The gas token on OP Mainnet is ETH. The OP token is a governance token, used for voting in the Collective, not for gas.
A fee has two parts:
- L2 execution fee: gas used times a low gas price, with an EIP-1559 style base fee.
- L1 data fee: the cost of posting your transaction data to Ethereum. It moves with Ethereum gas and blob prices.
Your wallet shows them as one amount. Simple transfers usually cost a fraction of a cent. Fees rise when OP Mainnet is busy or when Ethereum data costs rise. See the gas tracker for current prices including the L1 data fee, and gas and fees.
Addresses and tokens
Optimism uses the same 0x addresses as Ethereum and other EVM chains. Your balance on Optimism is separate from your balance on other chains. Tokens use the ERC-20 standard. Some tokens, such as USDC, have both a native version and an older bridged version. Check which one an app uses. See stablecoins.
How Optimism compares
| Optimism | Base | Arbitrum | Polygon | |
|---|---|---|---|---|
| Builder | OP Labs / Collective | Coinbase | Offchain Labs | Polygon Labs |
| Type | Optimistic rollup | Optimistic rollup | Optimistic rollup | Own PoS chain |
| Gas token | ETH | ETH | ETH | POL |
| Governance token | OP | None | ARB | POL |
See why fees differ between chains and the Arbitrum guide.
What to watch out for
- Wrong network. The same 0x address exists on every EVM chain. Pick the network that matches the receiver's expectation, for example "OP Mainnet" or "Optimism" on an exchange.
- Seven-day exit. The official bridge takes about a week to Ethereum. Third-party bridges are faster but add risk. See bridges and their risks.
- Centralized sequencer. One operator orders transactions.
- Upgrade keys and contract risk. Rollup contracts can have admin controls. Read the current documentation on decentralization.
- Scams. Fake OP airdrops and phishing links are common.
Follow Optimism live on ChainMonitor
- Live blocks: tiles with the fill level and fees paid per block.
- Recent blocks list and the header search for transactions and addresses.
- Gas tracker: cost of a send, USDC transfer and swap on Optimism, with the L1 data fee.
- RPC health for Optimism: public endpoints ranked by latency and lag.
Frequently asked questions
What is the difference between Optimism and Arbitrum?
Both are optimistic rollups on Ethereum with ETH as gas. Optimism uses the open-source OP Stack, also used by Base. Arbitrum uses Offchain Labs' Nitro software. Users see similar fees and tools.
What is the OP token used for?
OP is a governance token. Holders can take part in decisions of the Optimism Collective. It is not used to pay transaction fees.
Is Optimism the same as OP Mainnet?
In everyday use, yes. OP Mainnet is the name of the chain. Optimism is the broader project and community.
What is the Superchain?
It is the idea of many OP Stack chains, such as OP Mainnet and Base, that share software and standards and aim to work well together.
Do I need OP to send transactions on Optimism?
No. You need ETH on Optimism for fees.
How long does it take to withdraw from Optimism to Ethereum?
About seven days through the standard bridge. Third-party bridges can be faster for a fee.