| Authors | Optimism Team (Karl Floersch, Jinglan Wang, Kevin Ho) |
|---|---|
| Year | 2019 |
| Project | Optimism |
| License | MIT |
| Official Source | https://community.optimism.io/docs/protocol/explainer/ |
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Optimism is an Optimistic Rollup scaling solution for Ethereum developed by OP Labs (formerly Plasma Group), with initial technical publications beginning around 2019 and continuous spec updates through the present. The original core team included Karl Floersch, Jinglan Wang, and Kevin Ho, with substantial contributions from Ethereum researcher Ben Jones and many others. The canonical technical reference is the Optimism Protocol Documentation and the OP Stack specification.
Optimism processes Ethereum-compatible transactions off-chain, posts compressed data to Ethereum for data availability, and relies on a fraud proof challenge window to detect any invalid state claims by the sequencer.
> Source: Optimism’s technical specifications are at specs.optimism.io and community.optimism.io. The original “OVM” technical spec was at optimism.io and on GitHub.
Publication and Context
Optimism grew out of Plasma Group, one of the teams that worked on Plasma implementations. After the data availability problem killed Plasma for generalized computation, they pivoted to Optimistic Rollups — which solve data availability by posting all transaction data to Ethereum.
The “optimistic” in Optimistic Rollup refers to the fraud proof model: the sequencer is trusted optimistically. Its output (the state root) is accepted as valid unless someone posts a fraud proof within the challenge window.
Optimism mainnet launched in January 2021 (restricted) and fully in December 2021. The OP Stack was open-sourced in 2023, spawning the “Superchain” — a family of OP-based chains including Base (Coinbase), Mode, Zora, and many others.
Core Architecture
Transaction flow:
- User sends a transaction to the Optimism sequencer (a centralized server, currently operated by OP Labs)
- Sequencer orders transactions, executes them using the EVM, and produces a new state root
- Sequencer posts compressed transaction data (calldata or blobs post-EIP-4844) to Ethereum
- Sequencer posts a proposed state root to the L2OutputOracle contract on Ethereum
- A 7-day challenge window opens
If the state root is valid: After 7 days with no successful challenge, withdrawals can process.
If the state root is invalid: Anyone can submit a fraud proof (now called “fault proof”) within the 7-day window, which triggers the dispute game.
EVM Equivalence
Optimism’s key differentiator from earlier L2 designs is EVM equivalence: the L2 executes transactions using the same EVM as Ethereum mainnet. This means:
- Any Ethereum dApp deploys on Optimism with zero (or trivial) code changes
- Developer tooling (Hardhat, Foundry, Remix) works identically
- Smart contract bytecode is the same
Earlier L2 designs used “OVM” (Optimistic Virtual Machine), a sandboxed EVM-like environment. EVM equivalence replaced this for better compatibility, launched in 2022.
Fault Proof System
Optimism went through several iterations of its fraud proof system before deploying a production-ready Cannon fault proof in mid-2024. The Cannon system uses a bisection game:
| Step | Description |
|---|---|
| 1. Challenger claims | Challenger asserts a specific L2 block is invalid |
| 2. Bisection game | Challenger and defender alternate narrowing down the disputed execution step to a single EVM instruction |
| 3. Single instruction | The disputed single EVM instruction is executed on Ethereum (via MIPS emulation) |
| 4. Resolution | The on-chain execution determines who was right |
The Cannon system was significant because it removed the dependency on a trusted Security Council and made Optimism’s fraud proofs permissionless — anyone can challenge.
The OP Stack and Superchain
The OP Stack is Optimism’s modular rollup framework, released as open-source software. It lets anyone deploy a rollup sharing security and bridging infrastructure with the Optimism network. The vision is a Superchain — a network of interoperating OP-based chains that share:
- A common sequencer (or decentralized sequencer set)
- Unified cross-chain messaging
- Shared security from Ethereum
Superchain members (as of 2024): Base (Coinbase), Mode Network, Zora, Public Goods Network, Frax Finance, and dozens more.
OP Token and Governance
The OP token governs the Optimism Collective — a bicameral governance system:
- Token House: OP holders vote on protocol upgrades and treasury allocations
- Citizens’ House: Non-transferable “RetroPGF” allocations reward public goods contributors
The Retroactive Public Goods Funding (RetroPGF) model distributes sequencer revenue to open-source projects that benefit the Ethereum ecosystem.
Reality Check
Optimism’s fault proof system launched 3+ years after mainnet — withdrawals were secured by a trusted multisig during that period. The centralized sequencer remains an MEV and censorship concern; decentralized sequencing is planned but not yet delivered. Despite this, Optimism (and Base, its largest Superchain member) are among the highest-activity L2s by volume and users.
Related Terms
Research
- Ho, K., Floersch, K., & Wang, J. (2019). Optimistic Rollup. ethresear.ch.
— Original conceptual post introducing the term and the fraud proof model.
- OP Labs. (2023). OP Stack Specification. specs.optimism.io.
— The current canonical technical reference for the OP Stack.
- Thibault, L., Bocek, T., & Stiller, B. (2022). Blockchain Scaling Using Rollups: A Comprehensive Survey. arXiv:2202.07662.
— Comparative analysis placing Optimism in the broader rollup landscape.