🔮 Optimistic Rollups: Assume Valid, Challenge Later
Learn how Arbitrum and Optimism use fraud proofs for scaling
Compare the two dominant rollup approaches
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0 / 5 completed🔮 Optimistic Rollups Deep Dive
Optimistic rollups assume all transactions are valid by default—hence "optimistic." This trust-but-verify approach enables fast execution with a safety net: fraud proofs.
⚙️ How It Works
Batch Transactions
Sequencer collects L2 transactions and bundles them into batches (typically every few minutes).
Post to L1
Batch data and new state root posted to Ethereum mainnet as calldata (cheap storage).
Challenge Period
7-day window where anyone can challenge invalid state transitions with fraud proofs.
Finalization
If no valid challenges appear within 7 days, state is considered final and withdrawals are enabled.
🎮 Interactive Fraud Proof Simulator
Watch how the fraud proof mechanism protects optimistic rollups from invalid transactions.
1. Normal Operation
Sequencer posts transaction batch to L1
Batch #1234: 5,000 transactions posted to Ethereum mainnet. All transactions assumed valid by default.
🛡️ Security Model
✓ Advantages
- •Fast execution: Transactions confirm in seconds, not minutes
- •EVM compatible: Easy to port existing Ethereum dApps
- •Lower costs: No expensive proof generation required
- •Simpler: Less complex cryptography than ZK rollups
⚠️ Trade-offs
- •7-day withdrawals: Must wait for challenge period to end
- •Watcher dependency: Relies on honest validators monitoring
- •Higher data costs: Must post full transaction data to L1
- •Reactive security: Problems fixed after they occur
🌐 Real-World Implementations
Arbitrum
Largest optimistic rollup by TVL ($2B+)
Optimism
Founded by Ethereum Foundation alumni
Base
Coinbase's L2, built on OP Stack