What Is OP Mainnet?
TL;DR: OP Mainnet is Optimism's Ethereum Layer 2 network. It processes transactions faster and at a fraction of Ethereum's cost, while inheriting Ethereum's security. It is the original production network where the OP Stack was built and tested, and the starting point for teams before they launch their own dedicated chain.
OP Mainnet is a public blockchain network built on the OP Stack that runs Ethereum-compatible transactions at significantly lower cost and higher throughput than Ethereum mainnet. Every application that works on Ethereum works on OP Mainnet with no code changes. It settles its transaction data back to Ethereum, which is where the security comes from.
When developers say they're building on Optimism, they're usually building on OP Mainnet.
What OP Mainnet Does
Ethereum processes roughly 27 transactions per second at peak capacity. That ceiling created congestion, and congestion created fees that made Ethereum impractical for most everyday use.
OP Mainnet was built to extend Ethereum's capacity without compromising its security. It batches thousands of transactions together, executes them off the main chain, and posts compressed proof data back to Ethereum at regular intervals. The settlement layer remains Ethereum. The execution layer is OP Mainnet.
The practical result: transaction fees that typically run fractions of a cent, fast finality, and full compatibility with every Ethereum wallet, developer tool, and smart contract. For users, it means applications that actually run at usable cost. For developers, it means the same code they'd write for Ethereum, deployed without changes. For enterprises, it means Ethereum's audit trail and security at the throughput and cost structure that makes production infrastructure viable.
Why It Was Built
Ethereum was the most credibly neutral settlement layer ever built. The problem was scaling it without sacrificing what made it worth trusting.
Optimism deployed OP Mainnet in 2021 as the first major optimistic rollup in production. It was not a testnet or a research prototype. It was a live network carrying real transaction volume, built to prove that the OP Stack architecture could work under production conditions. Every subsequent development on the OP Stack, the fault proof system, Flashblocks, the interoperability work currently in development, was validated against real usage on OP Mainnet first.
That history matters. The engineering decisions that now run under Base, Sony Soneium, Kraken Ink, and OKX X Layer were all shaped by what OP Mainnet taught about operating L2 infrastructure at scale.
Who Runs on OP Mainnet
OP Mainnet is a shared public network, which means any developer can deploy on it and any user can transact on it without permission. The application ecosystem reflects that openness.
Uniswap generated $159 million in revenue running on OP Mainnet and its dedicated chain. World, the identity network with tens of millions of users, started on OP Mainnet before graduating to its own OP Stack chain. ether.fi, which processes $2 million in daily real-world payment volume and carries $160M+ in TVL across 70,000 active debit cards, all built on OP Stack infrastructure that has OP Mainnet at its origin.
Across all OP Stack chains, the network handled 3.6 billion transactions in late 2025, roughly 13 percent of total crypto activity at the time. OP Mainnet sits at the center of that production history as the shared network with the longest track record.
OP Mainnet vs. Ethereum Mainnet
OP Mainnet and Ethereum mainnet are not alternatives to each other. OP Mainnet is a scaling layer that runs on top of Ethereum. Assets and data move between the two. Security flows from Ethereum to OP Mainnet, not the other way.
OP Mainnet | Ethereum Mainnet | |
|---|---|---|
Transaction cost | Fractions of a cent | Variable, often dollars |
Block time | ~250ms | ~12 seconds |
Security model | Inherits Ethereum's security via fraud proofs | Native Ethereum consensus |
Smart contract support | Full EVM equivalence | Native |
Best for | Applications, DeFi, payments, user-facing activity | High-value settlement, security-critical finality |
Nothing is lost by running activity on OP Mainnet. The same wallets, the same developer tools, and the same contracts all work. For most applications, OP Mainnet is where transactions happen and Ethereum is where the security is anchored.
OP Mainnet vs. Owning Your Own Chain
OP Mainnet is a public network with shared block space. That means no dedicated throughput, no custom transaction fee structure, and no sequencer economics. For most teams starting out, that is exactly right: no infrastructure to manage, no sequencer to operate, and immediate access to an existing user base and application ecosystem.
The teams that move beyond OP Mainnet do so when dedicated infrastructure makes economic sense. The transition does not require additional retooling. The same OP Stack architecture, the same tooling, and the same developer experience move with the team. OP Mainnet is where the proof of concept becomes a production application. A dedicated chain is where a production application becomes a business with its own economics.
Frequently Asked Questions
Is OP Mainnet the same as Optimism?
OP Mainnet was previously called "Optimism." It was renamed in 2023 to distinguish the network from Optimism the company and the OP Stack technology framework. The network, the technology stack, and the company share a history but now have distinct names. OP Mainnet refers specifically to the public network. OP Stack refers to the open-source technology. Optimism refers to OP Labs, the team that builds and maintains both.
Is OP Mainnet secure?
OP Mainnet's security comes from Ethereum. Transaction data is posted to Ethereum, and OP Mainnet's fault proof system, rebuilt from scratch with a fully permissionless architecture, allows anyone to verify that the network's state is correct. The network does not ask users to trust Optimism. It gives users the tools to verify independently.
How does OP Mainnet keep fees low?
OP Mainnet batches transactions and compresses them before posting to Ethereum. With EIP-4844 blobs, introduced in Ethereum's Dencun upgrade, data posting costs dropped more than 90%. OP Mainnet fees reflect the cost of that data availability, not the full cost of executing directly on Ethereum mainnet.
What can you build on OP Mainnet?
Anything that runs on Ethereum runs on OP Mainnet. That includes DeFi protocols, payment applications, NFT platforms, stablecoin infrastructure, and enterprise financial applications. The network has been live since 2021 and carries hundreds of deployed applications.
What is the difference between OP Mainnet and Base?
Base is Coinbase's dedicated L2, built on the OP Stack. OP Mainnet is the original public network, also on the OP Stack. Both run on the same underlying technology and share the same engineering lineage. They operate as separate chains with different operators, different user ecosystems, and different economic structures. Base is a dedicated chain; OP Mainnet is the shared public network.
What is the OP Stack?
The OP Stack is the open-source software framework that powers OP Mainnet and every chain that has launched using the same architecture. It is MIT-licensed, meaning any team can use it, fork it, and build on it. OP Mainnet is both the original deployment of the OP Stack in production and the shared public network anyone can use today. Read the docs