Short answer: Layer-2 rollups execute transactions off Ethereum and post compressed proofs or data back to it, cutting fees by one to two orders of magnitude while inheriting Ethereum's security. Optimistic rollups (Arbitrum, Optimism, Base) are cheap and mature but have a seven-day native withdrawal window; zero-knowledge rollups (zkSync and peers) prove correctness cryptographically and can finalise much faster.
Why rollups exist
Ethereum deliberately limits how much computation fits into a block, because every node must verify everything. That constraint is what makes it credibly neutral, and also what made a simple swap cost more than a restaurant meal during peak periods. Rollups keep the security model and move the execution elsewhere: transactions are processed off-chain, then a compressed record is published on Ethereum where anyone can verify it.
Two proof models
| Optimistic rollup | ZK rollup | |
|---|---|---|
| Assumption | Transactions are valid unless challenged | Validity is proven cryptographically |
| Native withdrawal to L1 | ~7 days (challenge period) | Minutes to hours |
| Cost profile | Very low | Very low, higher proving overhead |
| EVM compatibility | Excellent, near drop-in | Good and improving |
| Examples | Arbitrum, Optimism, Base | zkSync, Linea, Scroll, Starknet |
The seven-day wait applies only to the native bridge. Third-party liquidity bridges exit in minutes for a fee, by fronting you the funds on Ethereum and taking the slow path themselves.
The main networks in practice
- Arbitrum — the largest optimistic rollup by activity, with the deepest DeFi liquidity and the widest protocol coverage. A safe default when you want the most options.
- Optimism — the other major optimistic rollup, notable for the OP Stack that many other chains are built from, and for public-goods funding as a design principle.
- Base — built on the OP Stack, distinguished by consumer and social applications and by a large mainstream on-ramp.
- zkSync, Linea, Scroll, Starknet — the ZK cohort. Faster finality to Ethereum and strong cryptographic guarantees; ecosystems are smaller but growing.
How to choose
- Follow the application. If the protocol or counterparty you need lives on one chain, that is your answer.
- Check liquidity for your pair. A marginally cheaper chain with thin liquidity costs more in slippage than it saves in gas.
- Consider exit speed. If you will move funds back to Ethereum frequently, a ZK rollup or a liquidity bridge matters.
- Note the gas token. Most L2s use ETH for gas, so keep a small ETH balance on the chain you use.
Risks worth naming
- Sequencer centralisation. Most rollups still run a single sequencer, which can censor or halt ordering — though users retain a path to force transactions through L1.
- Upgradeable contracts. Several rollups can be upgraded by a multisig or security council, a meaningful trust assumption.
- Bridge risk. Third-party bridges are separate systems with their own history of exploits.
Key takeaways
- Rollups keep Ethereum's security and cut costs dramatically.
- Optimistic rollups are mature; ZK rollups exit to L1 faster.
- Choose by application and liquidity, not by headline fee.
- Sequencer and upgrade powers are the real trust assumptions today.
You can receive assets directly on Arbitrum, Optimism, Base and other supported networks without bridging — pick the network on the exchange calculator or browse supported networks.
Frequently asked questions
Are Layer-2 networks as safe as Ethereum?
They inherit Ethereum's data availability and settlement, which is a strong foundation, but they add their own assumptions — sequencer operation and upgradeable contracts. In practice they are safer than an independent chain and not yet identical to Ethereum itself.
Why does withdrawing from Arbitrum take seven days?
Optimistic rollups publish results as presumed valid and allow a challenge window for anyone to submit a fraud proof. The waiting period is that window. Liquidity bridges bypass it for a fee.
Do I need ETH on a Layer-2 to transact?
Yes on most of them, since ETH is the gas token. Even a few dollars is usually enough for many transactions at L2 prices.
