KoinlyticsArbitrum and Optimism are the two dominant optimistic rollups on Ethereum. They started with different fraud proof designs and diverged further as their ecosystems matured.
Fraud proofs
Arbitrum uses multi-round interactive fraud proofs. Disputants narrow down the disagreement in a bisection game, and only the final step gets executed on L1. Cheaper on the happy path, more complex protocol.
Optimism uses single-round fraud proofs (as of Cannon and beyond). Simpler to reason about, potentially more expensive to challenge.
Ecosystem
- Arbitrum is DeFi-heavy: GMX, Camelot, Pendle, dopex all live here. Bigger TVL, thicker orderbooks for perps.
- Optimism is consumer + Superchain: Base runs on OP Stack, Farcaster settled here, Coinbase's flywheel is entirely OP Stack.
Governance
Both have on-chain governance with their own tokens (ARB, OP). Optimism pioneered the retroactive public goods funding model (RetroPGF). Arbitrum runs its DAO and has funded major grants (Arbitrum DAO Foundation).
App-chain paths
Arbitrum Orbit lets projects launch their own L3 that settles to Arbitrum. Optimism's Superchain lets you launch a chain in the OP Stack ecosystem. Both have real traction: Orbit chains include XAI (gaming) and Arbitrum Nova.
Which to build on
Building DeFi that needs deep pools: Arbitrum. Building consumer + social with Coinbase distribution: Base (on OP Stack). Deploying an appchain: pick the ecosystem that already has your target users.