What Is the OP Stack?

TL;DR The OP Stack is an open-source, MIT-licensed framework for building Ethereum Layer 2 chains. It's the most widely deployed chain-building framework in production - more than 50 chains, including Ink, Unichain, and Sony's Soneium, run on it today.

• 50+ chains in production; more than 70% of all L2 transaction volume

• $16B+ in assets secured across the ecosystem

• MIT-licensed, no fees to Optimism; sequencer revenue belongs entirely to the operator

• Full EVM equivalence - Ethereum contracts deploy without modification

• Fully managed deployment available through OP Enterprise

Ink, Unichain, Sony Soneium, X Layer, World, Bitpanda's Vision Chain, and OP Mainnet are among the 50+ chains running on the OP Stack today.

Ethereum has a throughput ceiling. Roughly 15 transactions per second, with fees that spike into tens of dollars during high-demand periods. The OP Stack exists to remove that ceiling without compromising Ethereum's security.

It is an open-source framework for building optimistic rollup chains that settle to Ethereum. Every chain built on it inherits Ethereum's security, posts transaction data back to Ethereum, and runs at throughput many orders of magnitude beyond what Ethereum mainnet supports directly. Transaction fees on OP Stack chains measure in fractions of a cent. Block times measure in seconds.

What is the OP Stack?

The OP Stack is the software framework used to build Ethereum Layer 2 chains. It defines every layer of the stack: how transactions are ordered and batched, how data is posted to Ethereum, and how the chain's state is committed and verified.

The code is MIT-licensed and every chain deployed on it shares the same architecture and security model.

How do OP Stack chains work?

An OP Stack chain is an optimistic rollup. It processes transactions off Ethereum, compresses them into batches, and posts those batches back to Ethereum at regular intervals. Ethereum stores the transaction data and serves as the settlement layer. The computation happens on the rollup. The security guarantee comes from Ethereum.

The name "optimistic" describes the security model. Submitted transactions are assumed valid by default. Anyone who believes a batch contains an invalid state can challenge it using the fault proof system, which runs entirely on Ethereum. If a challenge succeeds, the invalid batch is rejected. If no valid challenge is submitted within the defined window, the state is finalized.

This model gives OP Stack chains full EVM equivalence. Smart contracts written for Ethereum deploy without modification. Any application that works on Ethereum works on an OP Stack chain with no code changes required.

The security model has two outcomes: if a valid challenge is submitted within 7 days, the invalid batch is rejected. If no valid challenge arrives, the state is finalized on Ethereum.

OP Stack architecture

Five core components connect to Ethereum: the sequencer handles transaction ordering, the batcher posts compressed data to L1, the proposer commits state roots, the fault proof system enforces correctness, and L1 smart contracts define security rules and handle withdrawals.

Transaction lifecycle

A user transaction moves from sequencer soft-confirmation (seconds) through Ethereum data posting, state commitment, and a 7-day fault proof window before reaching economic finality on Ethereum.

Sequencer

The node responsible for ordering incoming transactions, building blocks, and batching them for submission to Ethereum. The sequencer is where the chain's economics live: transaction fees come in, data posting costs go out, and the difference is sequencer revenue. The sequencer is also the liveness-critical component.

Batcher

The component that compresses transaction batches and posts them to Ethereum. Since EIP-4844 (Ethereum's Dencun upgrade in March 2024), batches are posted as blobs, a dedicated data format that cut rollup posting costs by more than 90% compared to earlier calldata methods. Batcher costs are the primary ongoing operating expense for any chain and scale with transaction volume.

Proposer

Posts output roots to Ethereum at regular intervals. An output root is a cryptographic commitment to the chain's current state. It is what the fault proof system references when detecting invalid state transitions.

Fault proof system

OP Stack's security layer. Anyone can challenge an output root they believe is incorrect. The challenge runs entirely on Ethereum without requiring permission from Optimism or any other party. The permissionless fault proof system was rebuilt from scratch and shipped in 2024. Before that, a security council held override authority. Now the challenge game is fully on-chain, with no trusted intermediary in the path.

L1 contracts

The set of smart contracts deployed to Ethereum mainnet that define the chain's security rules, handle deposits and withdrawals, and anchor the chain's state to Ethereum. These contracts are audited, production-tested across 50+ chains, and used without modification by most OP Stack deployments.

Who builds on the OP Stack?

More than 50 chains are live in production on the OP Stack. Together they secured more than $16 billion in assets and processed 6 billion transactions in 2025, representing 29 times growth in 12 months. OP Stack chains handle more than 70% of all L2 transaction volume.

The range of use cases covers most of the industry's major verticals. Base is a general-purpose consumer L2. Unichain is purpose-built for DeFi trading. Soneium targets media and entertainment. Kraken Ink and OKX X Layer serve exchange users. Bitpanda launched Vision Chain as the first fully regulated EU exchange chain, with OFAC screening built into the protocol. ether.fi runs onchain payment infrastructure on OP Mainnet, processing $2 million in daily payment volume with 70,000 active cards.

Why do teams choose the OP Stack over deploying on an existing chain?

The decision typically comes down to two things: control over block space and economics.

Teams that generate significant transaction volume reach a point where sequencer revenue makes dedicated infrastructure worthwhile. A top-3 US exchange generated $75 million in sequencer revenue in H2 2025 by running on the OP Stack. That revenue belongs entirely to the chain operator.

Full EVM equivalence removes the migration friction that other frameworks introduce. Every contract, dev tool, and wallet integration carries over.

The production record matters too. That operating history runs across exchange infrastructure, consumer payments, and DeFi protocols at scale. Architecture decisions for blob posting, fault challenges, and sequencer uptime have been tested against billions of real transactions, not simulated ones.

How does the shared codebase benefit every chain operator?

Every OP Stack chain gets improvements made by any team working on the codebase. When OP Labs ships a performance fix, it's available to every operator. When Ink or another chain resolves an issue, the fix propagates across the framework. No individual chain has to maintain the shared infrastructure on its own.

The fault proof system is maintained and improved by OP Labs. Security patches are applied across all production deployments. Operators using OP Enterprise receive patches within hours of identification.

What is OP Enterprise?

OP Enterprise is Optimism's managed chain service for organizations that want to run on the OP Stack without owning the full infrastructure operations. Three tiers cover a range of operating models, from fully managed SaaS to self-operated with OP Labs support.

Fully Managed

OP Labs operates the sequencer, batcher, proposer, and all chain infrastructure as a SaaS service on Optimism's servers. Customers receive a production mainnet and testnet with no infrastructure to manage. Designed for teams that want to run a dedicated chain without building or operating the underlying stack.

Self Managed

For organizations that run their own chain on their own infrastructure and want OP Labs expertise behind them. The customer controls the sequencer and all node infrastructure. OP Labs provides support, security and bridge monitoring with runbooks, custom engineering hours, and security and performance assessments. Designed for teams with strong internal infrastructure capacity that want OP Labs coverage without giving up operational control.

OP Mainnet

Deploy directly on OP Mainnet and access the scale and liquidity of one of the largest L2s - no chain infrastructure to operate. Free to deploy.

Mission Critical Add-On

Available as an add-on to Fully Managed and Self Managed. Upgrades to a 99.95% uptime SLA, 15-minute P1 initial response with 30-minute status updates, a dedicated Technical Account Manager, quarterly business reviews, and OP engineer presence in your war room for critical incidents or major launch events.

OP Enterprise also includes access to Optimism's partner network, covering stablecoin issuers, oracle providers, bridges, wallet teams, and block explorers. Partner integrations that typically take months of individual negotiation compress to weeks through the existing network.

What's next for the OP Stack?

Interoperability is the current development focus. Each OP Stack chain today operates independently, and moving assets between two of them requires a bridge. When the interoperability upgrade ships, any two OP Stack chains will exchange assets and messages natively, without a bridge. The initial target is OP Mainnet and Unichain.

Frequently Asked Questions

What is the difference between the OP Stack and OP Mainnet?

OP Mainnet is a specific chain built on the OP Stack framework. The OP Stack is the underlying software framework used to build OP Mainnet and all other chains that share its architecture. "OP Stack" refers to the codebase and framework. "OP Mainnet" refers to the specific production chain that Optimism operates.

What smart contract languages does the OP Stack support?

Any language that compiles to EVM bytecode: Solidity, Vyper, and others. Full EVM equivalence means Ethereum contracts deploy on an OP Stack chain without modification.

How long does it take to launch an OP Stack chain?

Self-operated deployment typically runs 8 to 12 weeks from start to mainnet, assuming technical resources are in place and key configuration decisions have been made in advance. Managed deployment through OP Enterprise typically runs 6 to 8 weeks. The binding constraint on most timelines is partner integrations, not the engineering.

What is the OP Stack's relationship to Ethereum?

OP Stack chains settle to Ethereum. Transaction data is posted to Ethereum, and the chain's state is anchored through output roots. Ethereum provides the security guarantees. The OP Stack provides the execution layer that makes high-throughput, low-cost transactions possible while keeping Ethereum as the trust anchor.

Can I configure an OP Stack chain for my use case?

Yes, the OP Stack is modular and configurable. Teams can set a custom gas token, configure compliance screening at the sequencer level, choose alternative data availability layers, and modify other default behaviors. Configuration decisions made before deployment are hard to change after launch. Custom modifications to core contracts require a security audit before production deployment.

Glossary

Optimistic rollup - A Layer 2 approach that processes transactions off Ethereum, posts compressed batch data to Ethereum for storage, and assumes submitted state transitions are valid unless challenged within a set window.

Sequencer - The node that orders incoming transactions, builds blocks, and batches them for submission to Ethereum. The sequencer is where chain economics concentrate: fees in, data-posting costs out, the difference is operator revenue.

Batcher - The component that compresses transaction batches and posts them to Ethereum as blobs. The batcher's data-posting costs are the primary ongoing operating expense for any OP Stack chain.

Proposer - Posts cryptographic output roots to Ethereum at regular intervals. Output roots are the commitments the fault proof system uses to detect invalid state transitions.

Fault proof - The on-chain dispute mechanism that lets anyone challenge an invalid output root on Ethereum, without permission from Optimism. Rebuilt from scratch and shipped in 2024.

EVM equivalence - Full compatibility with the Ethereum Virtual Machine. Smart contracts written for Ethereum deploy on an OP Stack chain without modification.

EIP-4844 / blobs - An Ethereum upgrade (March 2024) that introduced a dedicated low-cost data format for rollups. Blob posting cut OP Stack data submission costs by more than 90% vs. the prior calldata method.

Output root - A cryptographic commitment to an OP Stack chain's current state, posted to Ethereum by the proposer. The reference point for fault challenges.

Fully Managed - OP Enterprise's fully managed tier: OP Labs operates the sequencer and all chain infrastructure as a SaaS service. Customers get a production mainnet and testnet with no infrastructure to manage.

Self Managed - OP Enterprise's self-operated tier. The customer runs the sequencer and all nodes; OP Labs provides support, monitoring, security advisories, and custom engineering hours.

OP Mainnet - Optimism's flagship L2, free to deploy on. For teams that want Ethereum L2 scale and liquidity without running their own chain.

Mission Critical Add-On - A premium support tier available with Fully Managed and Self Managed. Adds a 99.95% uptime SLA, 15-minute P1 response, a dedicated Technical Account Manager, quarterly business reviews, and war-room support for critical incidents.