Ethereum transactions can become expensive just when you need the network most. Moving to a Layer 2 may reduce those costs, but unfamiliar bridges, delayed withdrawals, and similarly named projects can make the switch confusing.
OP Mainnet—formerly known as Optimism—offers an Ethereum-compatible alternative, but you should understand how it works and where its security assumptions begin before moving your assets.
Table of Contents
What Is OP Mainnet?
OP Mainnet is a production Ethereum Layer 2 blockchain powered by optimistic rollup technology. It was formerly called Optimism and Optimistic Ethereum. Rather than replacing Ethereum, OP Mainnet extends its capacity by moving transaction execution to Layer 2 while relying on Ethereum Mainnet for settlement and data availability.
OP Mainnet is EVM-compatible, so developers can deploy Solidity smart contracts and use familiar Ethereum tools. Many applications can migrate to OP Mainnet with relatively few code changes.
The following terms describe different parts of the same ecosystem:
- OP Mainnet is the live Ethereum Layer 2 blockchain.
- The OP Stack is the open-source software framework used to build OP Chains, including OP Mainnet.
- The Optimism Collective is the governance organization supporting the ecosystem.
- The Superchain is a broader ecosystem of OP Chains coordinated around shared OP Stack standards and services.
OP Mainnet is an OP Chain and one of the main deployments associated with the Superchain. It settles on Ethereum Mainnet and uses Ether, or ETH, to pay transaction fees.
Why Does Ethereum Need OP Mainnet?
Ethereum Mainnet is a Layer 1 blockchain and settlement network, but its capacity is limited. When demand rises, you compete with other users for block space, which can increase transaction fees and confirmation times. These conditions can make applications less accessible, particularly when you regularly use DeFi services.
OP Mainnet addresses this problem through Layer 2 scaling. It executes transactions on a separate network, batches the resulting data, and publishes that data to Ethereum. This reduces the amount of computation Ethereum must perform directly while preserving Ethereum-backed settlement and data availability.
As an optimistic rollup, OP Mainnet assumes that state proposals are correct unless someone successfully challenges them. A fault proof system provides a process for disputing invalid proposals during the challenge period.
OP Mainnet is also EVM-compatible. You can use familiar smart contracts, wallets, and development tools instead of interacting with an entirely different blockchain environment.
How Does OP Mainnet Work?
An OP Mainnet transaction moves through several components before it reaches Ethereum-backed settlement. The main stages are submission, sequencing, execution, batch publication, state verification, and finalization.
Transaction Submission
You submit a transaction through a wallet, decentralized application, or RPC provider. The transaction uses ETH for gas, although OP Mainnet fees are usually lower than comparable Ethereum L1 fees.
The sequencer receives the Layer 2 transaction and places it in an ordered queue. It then provides a rapid soft confirmation, allowing you to see that the transaction has been accepted locally. This isn’t yet the same as Ethereum-backed transaction finality.
Sequencing
The sequencer orders transactions and produces a Layer 2 block. It also creates transaction receipts so applications and wallets can display the result.
The op-node consensus client interacts with the execution client and tracks the rollup’s derivation state. It uses data published to Ethereum Mainnet to help reconstruct the canonical OP Mainnet chain.
Layer 2 Execution
An execution client, such as op-geth or a compatible alternative, executes Layer 2 transactions. It processes smart contract calls, updates balances, and maintains the resulting OP Mainnet state.
The consensus and execution clients perform different jobs. The consensus client handles chain derivation and rollup consensus, while the execution client processes transactions and maintains the state.
Batch Publication
The op-batcher compresses Layer 2 transaction data into batches and submits them to Ethereum Mainnet. Depending on the current protocol configuration, the batch can use Ethereum blobs or calldata.
These published batches provide data availability. Independent participants can use the data to reconstruct the OP Mainnet chain, replay transactions, and support fault proof verification.
State Verification
The op-proposer publishes proposed Layer 2 state roots to Ethereum through the dispute game system. These proposals represent OP Mainnet’s state at a specific point and support the withdrawal process.
A challenger can monitor proposals and dispute an invalid one through the fault proof system. The DisputeGameFactory manages these dispute games, helping ensure that withdrawals rely on a valid state proposal rather than an incorrect claim.
Ethereum Settlement
Ethereum settlement is the final anchoring stage. OP Mainnet publishes transaction data and state information to Ethereum Mainnet, which provides the underlying settlement and data availability layer.
A soft confirmation can arrive quickly, but stronger finality depends on Ethereum. Once the relevant data is included in a finalized Ethereum block, the transaction has Ethereum-backed finality.
What Makes OP Mainnet an Optimistic Rollup?
An optimistic rollup executes transactions on Layer 2 while publishing enough information to Ethereum Mainnet for independent reconstruction and verification. OP Mainnet follows this model.
The system is called “optimistic” because it doesn’t require Ethereum to re-execute or immediately verify every proposed Layer 2 state. Instead, it accepts a proposal unless a participant identifies an error and submits a valid challenge through the fault proof system.
This design supports Layer 2 scaling while retaining Ethereum settlement and data availability. Transaction batches contain the Layer 2 transaction data, while state proposals represent the resulting OP Mainnet state.
If a state proposal is invalid, participants can dispute it during the challenge period. A successful challenge invalidates the incorrect state claim used for withdrawals. It doesn’t reverse the entire OP Mainnet transaction history.
Transaction Finality and the Seven-Day Withdrawal Period
OP Mainnet transaction finality occurs in stages. The sequencer can provide a soft confirmation within seconds, but this early confirmation depends on the sequencer and isn’t equivalent to Ethereum-backed finality.
A transaction receives stronger assurances after its data is published to Ethereum and the relevant Ethereum block is finalized. Ordinary Layer 2 activity therefore feels fast, while Ethereum provides the underlying settlement layer.
Canonical withdrawals work differently. A standard withdrawal from OP Mainnet to Ethereum must be proven on Ethereum and pass through a challenge period. The official bridge documentation specifies a seven-day completion period for OP Mainnet-to-Ethereum transfers.
Withdrawal finalization occurs on Ethereum after the required proof and waiting period are complete. The process is slower than an ordinary Layer 2 transaction, but it gives participants time to challenge an invalid withdrawal-related proposal.
OP Stack, OP Chains, and the Superchain
The OP Stack is a modular, open-source framework for building Ethereum Layer 2 networks and other OP Chains. It supplies components for execution, chain derivation, sequencing, data availability, and settlement interfaces.
OP Mainnet is one deployment of the OP Stack. Other OP Chains can use the same framework while configuring their own parameters, infrastructure, applications, and governance arrangements.
The Superchain is a blockchain ecosystem made up of OP Chains coordinated around shared OP Stack standards, upgrades, security arrangements, and services. OP Mainnet is part of this ecosystem, but simply forking the open-source OP Stack doesn’t automatically make a blockchain an official OP Chain or guarantee shared security and interoperability.
OP Labs develops core OP Stack software and contributes to the Superchain roadmap. The Optimism Collective supports governance and ecosystem coordination.
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Fees, Gas, and Performance
OP Mainnet fees generally cost less than equivalent transactions on Ethereum Mainnet, but they vary with network conditions. Factors include transaction complexity, compressed transaction size, Layer 2 demand, sequencing conditions, and Ethereum data prices.
An OP Mainnet transaction generally includes two primary fee components:
- L2 execution fee: Covers computation and storage performed on OP Mainnet.
- L1 data fee: Covers publication of compressed transaction data to Ethereum.
You pay OP Mainnet fees in ETH. The OP token isn’t the network’s gas asset.
The L1 data fee depends partly on Ethereum data costs and the size of the compressed transaction batch. As a result, OP Mainnet fees can change even when Layer 2 demand remains relatively stable.
What Can You Do on OP Mainnet?
OP Mainnet is a general-purpose, EVM-compatible blockchain. You can use it to:
- Send ETH and supported tokens
- Interact with smart contracts
- Trade on decentralized exchanges
- Lend or borrow through DeFi applications
- Use games, NFT platforms, and other Solidity-based applications
- Deploy Ethereum-compatible decentralized applications
Because OP Mainnet supports familiar Ethereum accounts and development tools, many applications can deploy with relatively little modification. This makes the Optimism network more than a payment network—it supports a broad application ecosystem.
You should still review contract risks, bridge risks, and application-specific security before depositing funds. Fees are usually lower than Ethereum L1 fees, but they can change with Layer 2 demand and Ethereum data costs.
The OP token is mainly used for governance rather than gas. Governance also supports ecosystem initiatives such as Retro Funding.
How Bridging to and From OP Mainnet Works
Bridging transfers assets or messages between Ethereum and OP Mainnet. The direction of the transfer affects how the process works and how long it takes.
- Deposits and withdrawals: A deposit starts on Ethereum Mainnet and moves assets to OP Mainnet. A withdrawal starts on OP Mainnet and moves assets to Ethereum. Canonical withdrawals require a challenge period before finalization.
- Standard Bridge: The Standard Bridge transfers ETH and most standard ERC-20 token representations between Ethereum and OP Mainnet. It uses bridge and messaging contracts, including the OptimismPortal and CrossDomainMessenger, to process deposits, withdrawals, and cross-chain messages.
- Third-party fast bridges: A third-party bridge may provide faster transfers by using liquidity providers. This convenience introduces additional smart contract, counterparty, and liquidity risks. It also doesn’t change the security assumptions or withdrawal period of the canonical bridge itself.
- Token representations: A token may have different contract addresses on different networks. Before bridging an ERC-20 token, verify its contract address, bridge route, and destination network.
Who Governs and Develops Optimism?
Several organizations and governance bodies contribute to Optimism, but none of them is the blockchain itself.
- Optimism Collective: The broader governance organization that coordinates parts of the Optimism and Superchain ecosystems.
- Token House: Represents OP tokenholders through token-weighted voting. Tokenholders can also delegate their voting power.
- Citizens’ House: Represents broader stakeholder interests using a one-member-one-vote model.
- OP Labs: Develops core OP Stack software, proposes protocol upgrades, and contributes to the Superchain roadmap.
- Optimism Foundation: Supports and stewards Optimism governance.
- Optimism Security Council: Holds defined protocol security and emergency responsibilities.
- Retro Funding: A public-goods funding program that rewards projects and contributors for their demonstrated impact.
Governance mechanisms and responsibilities can change as the Collective evolves. You should review current proposals and operating documents before participating in a vote or delegating OP.
Is OP Mainnet Secure and Decentralized?
OP Mainnet security relies on Ethereum settlement, published transaction data, state proposals, and the fault proof system. The sequencer provides fast transaction ordering and soft confirmations, while Ethereum supplies the underlying settlement and data availability layer.
Permissionless fault proofs went live on OP Mainnet on June 10, 2024. Participants with the required resources can propose or challenge withdrawal-related state claims through the dispute game system.
However, OP Mainnet decentralization has important limits. A single sequencer currently performs transaction ordering, while privileged upgrade and emergency powers remain. The Security Council and other authorized entities can intervene in defined circumstances, including responding to serious protocol risks.
For that reason, you shouldn’t treat OP Mainnet as completely trustless or fully decentralized. Its security model has improved through permissionless fault proofs, but you should still assess risks associated with:
- Protocol upgrades and privileged roles
- Sequencer operation and potential censorship
- Bridge contracts
- Third-party applications
- Governance decisions
- Smart contract vulnerabilities
Independent risk analysis currently classifies OP Mainnet as a Stage 1 optimistic rollup rather than a fully decentralized Stage 2 system.
What Is the OP Token?
The OP token is the governance token of the Optimism Collective. OP tokenholders can participate in Token House governance, vote on eligible proposals, and delegate voting power.
OP isn’t used to pay gas on OP Mainnet. You normally pay transaction fees in ETH, and the OP token doesn’t replace ETH as the network’s transaction-fee asset.
The OP token supports governance across parts of the Optimism and Superchain ecosystems. The Token House uses token-weighted voting, while the Citizens’ House represents other stakeholder interests through a separate governance model.
As with any governance token, you should consider voting, delegation, treasury, protocol, and market risks before buying or using OP.
History of the OP Mainnet
The first testnet version of Optimistic Ethereum went live in January 2020. An alpha mainnet began operating in January 2021, followed by unrestricted public smart contract deployment in December 2021.
The network was initially known as Optimism or Optimistic Ethereum. It became OP Mainnet in 2023 as the project expanded its focus toward the OP Stack and Superchain.
The Bedrock upgrade was activated in 2023. It redesigned major parts of the network’s architecture and established a foundation for later OP Stack development.
Permissionless fault proofs followed on June 10, 2024, expanding participation in the system used to propose and challenge withdrawal-related state claims. OP Mainnet and the wider OP Stack have continued to receive protocol upgrades since then.
OP Mainnet Compared with Common Alternatives
OP Mainnet shares Ethereum’s Layer 2 market with other optimistic rollups and OP Stack-based networks. The right option depends on the applications, liquidity, bridge routes, fees, governance, and security assumptions you prefer.
| OP Mainnet | Arbitrum One | Base | |
|---|---|---|---|
| Network type | Optimistic rollup | Optimistic rollup | Optimistic rollup |
| Technology stack | OP Stack | Arbitrum technology stack | OP Stack |
| Part of the Superchain | Yes | No | Yes |
| Gas asset | ETH | ETH | ETH |
| Separate network and ecosystem | Yes | Yes | Yes |
OP Mainnet vs. Arbitrum
Both OP Mainnet and Arbitrum are Ethereum Layer 2 networks that use optimistic rollup designs. Both execute transactions away from Ethereum and use Ethereum for settlement and data availability.
The main architectural difference is that OP Mainnet is built with the OP Stack and belongs to the Superchain ecosystem. Arbitrum uses its own technology stack and isn’t an OP Chain.
When comparing OP Mainnet vs. Arbitrum, review their fees, available applications, bridge designs, governance, sequencing arrangements, and fault proof systems rather than treating either network as universally safer or better.
OP Mainnet vs. Base
Base is also an OP Stack-based Ethereum Layer 2 and an OP Chain associated with the Superchain. It shares broad technical standards with OP Mainnet but remains a separate network with its own applications, infrastructure, configuration, and user base.
When comparing OP Mainnet vs. Base, consider application availability, liquidity, transaction costs, bridge options, governance, and ecosystem support. Their fees can differ because each network has its own demand and transaction patterns.
Final Thoughts
OP Mainnet gives you a faster, generally cheaper way to use Ethereum-compatible applications while retaining Ethereum as its settlement and data availability layer. Its EVM-compatibility and place within the Superchain make it useful for both users and developers. Still, lower fees don’t eliminate risk.
Before bridging funds, make sure you understand the seven-day canonical withdrawal period, fault proof system, centralized sequencer, privileged protocol roles, and the risks introduced by individual applications.
Disclaimer: Please note that the contents of this article are not financial or investing advice. The information provided in this article is the author’s opinion only and should not be considered as offering trading or investing recommendations. We do not make any warranties about the completeness, reliability and accuracy of this information. The cryptocurrency market suffers from high volatility and occasional arbitrary movements. Any investor, trader, or regular crypto users should research multiple viewpoints and be familiar with all local regulations before committing to an investment.
