Optimistic Rollups

What are Optimistic Rollups?

Optimistic rollups are Layer 2 scaling solutions that execute transactions off-chain while posting transaction data to the main chain. They assume transactions are valid by default (hence “optimistic”) and use fraud proofs to ensure security.

How They Work

Transaction Flow

1. Users submit transactions to L2 sequencer
2. Sequencer batches and orders transactions
3. Batches are posted to L1 as calldata
4. Challenge period begins (typically 7 days)
5. After challenge period, transactions are finalized

Fraud Proofs

If someone submits an invalid state:

1. Validators can submit fraud proof during challenge period
2. On-chain computation verifies the dispute
3. Invalid submitter is slashed
4. Honest challenger is rewarded

Advantages

• EVM Compatibility: Easy migration from Ethereum
• Lower Fees: 10-100x cheaper than L1
• High Throughput: Thousands of TPS
• Security: Inherits L1 security through fraud proofs

Disadvantages

• Withdrawal Delay: 7-day challenge period for exits
• Trust Assumptions: Requires at least one honest validator
• Data Availability: Must post all data to L1

Major Implementations

Rollup	Framework	TVL Rank
Arbitrum One	Arbitrum Nitro	#1
Optimism	OP Stack	#2
Base	OP Stack	#3

vs ZK Rollups

Aspect	Optimistic	ZK
Finality	~7 days	Minutes
Computation	Off-chain	Off-chain + proofs
EVM Support	Native	Complex
Cost	Lower	Higher (for now)