A Layer 2 is a network built on top of a blockchain that processes transactions separately, then posts the results back to the base chain. Security comes from the chain underneath. Fees are a fraction of it.
Scale arrived faster than most expected. By May 2026, 73 active rollups collectively held more than $48 billion in total value locked, against under $4 billion in 2023.
The problem Layer 2 solves
Ethereum's base layer is deliberately constrained. Every node processes every transaction. That is what makes it secure and decentralized, and also what caps throughput.
Two options existed. Raising base-layer capacity pushes up node hardware requirements and centralizes the network. Moving execution elsewhere does not.
Ethereum chose the second. Keep the base chain small and expensive to attack. Let other networks handle volume, settling back to it.
How a rollup works
Four steps.
- On the Layer 2 you transact, paying a small fee.
- Thousands of transactions get batched together by the sequencer.
- Compressed and posted to Ethereum, the batch arrives with a proof or a challenge period.
- Ethereum records it, and the Layer 2's state becomes final, inheriting whatever guarantees the base chain provides.
Costs fall because the expensive part, posting to Ethereum, gets shared across every transaction in the batch. Ten thousand transactions split one settlement bill.
Optimistic vs ZK rollups
How they prove the batch is honest is where the two architectures differ.
| Optimistic rollup | ZK rollup | |
|---|---|---|
| Assumption | Batches are valid unless challenged | Every batch carries a cryptographic proof |
| Withdrawal to Ethereum | 7-day fraud-proof challenge window | 1 to 24 hours |
| EVM compatibility | Very high | Improving, historically harder |
| Examples | Arbitrum, Base, OP Mainnet | zkSync Era, Starknet, Scroll |
On adoption, optimistic rollups lead, mainly because EVM compatibility made migration easy. On finality speed, ZK rollups win, which matters increasingly to institutional capital.
What Dencun changed
In March 2024 came the structural break that reset the entire economics of the sector.
Before then, rollups posted data to Ethereum as calldata, competing with every other transaction for the same block space. With EIP-4844 came blob-carrying transactions, a separate data lane priced independently and pruned after roughly 18 days.
Costs fell 80 to 90%. From a $0.50 to $5.00 range, median fees dropped to $0.001 to $0.05.
Knock-on effects ran larger than the fee change alone. Mainnet utilization fell to about 50% as load shifted upward. One network recorded a 224% rise in transaction volume once fees collapsed. And the competitive basis shifted, since fee differences between major networks now come down to cents.
The rollup market as it stands
Consolidation defines it. Capital and activity concentrate across a handful of networks far more heavily than the raw count of seventy-three active rollups would ever suggest to someone reading it cold.
Arbitrum One leads with roughly $16 to 17 billion in TVL, around 40 to 44% of the whole market. Following at approximately $11 to 12 billion is Base. OP Mainnet holds about $5.6 billion. Between them, those three process roughly 90% of all Layer 2 transaction volume.
Median fees in mid-2026: Base around $0.02 to $0.05, zkSync Era near $0.07, Arbitrum One and OP Mainnet around $0.09. On the cheapest networks, simple transfers fall below a tenth of a cent.
The risks of Layer 2 networks
- Sequencer centralization. Running a single sequencer lets a network censor or reorder transactions, and most rollups do. Decentralizing it remains work in progress.
- Upgrade keys. At Stage 0, a network's contracts can be changed by a small group holding private keys. Six major networks had reached Stage 1 by 2026, which is progress rather than completion.
- Withdrawal delays. Optimistic rollups impose a seven-day wait for canonical bridge withdrawals. Third-party bridges are faster and carry their own cross-chain risk.
- Fragmented liquidity. Scattered across 73 networks, assets are not pooled anywhere.
- Sequencer economics. Cutting per-transaction revenue to very thin margins pressures chains that rely on incentives rather than organic demand.
Where mb.io fits
Layer 2 networks reduce the cost of moving on-chain. Where you buy the assets in the first place is a separate question, and a regulated exchange answers it differently.
mb.io is a regulated crypto spot exchange backed by MultiBank Group, a financial institution founded in 2005 that serves more than 2 million clients across 100+ countries.
- Regulated by VARA in the UAE and AUSTRAC in Australia
- Deposit and withdrawal flows that name the network explicitly before funds move
- 10/10 security score from Hacken, an independent blockchain security auditor
- Institutional-grade MPC custody powered by Fireblocks, with segregated client funds
- Buy, sell, and swap in three steps, from sign-up to purchase
- 24/7 multilingual customer support
Open your account and start trading on mb.io.
Frequently asked questions
What is a Layer 2 in crypto?
A network built on top of a base blockchain that processes transactions separately and posts results back for settlement. Security is inherited from the base chain, and gas fees run far lower.
What is the difference between optimistic and ZK rollups?
Optimistic rollups assume batches are valid unless challenged, which needs a seven-day window before withdrawals finalize. Attaching a cryptographic proof to every batch, ZK rollups settle withdrawals in one to 24 hours.
Why did Layer 2 fees fall so sharply?
EIP-4844, part of the Dencun upgrade in March 2024, gave rollups a dedicated data lane called blobs. Data-posting costs fell 80 to 90%, taking fees from dollars down to fractions of a cent.
Is a Layer 2 as safe as Ethereum?
Not identically. Ethereum's settlement security is inherited, and new risks arrive alongside it: sequencer centralization, upgradeable contracts, and bridge exposure. Security maturity varies considerably between networks.
How much money is on Layer 2 networks?
More than $48 billion in total value locked across 73 active rollups as of May 2026, against under $4 billion in 2023.
Which Layer 2 has the most liquidity?
Arbitrum One, at roughly $16 to 17 billion in TVL, about 40 to 44% of the market. Second is Base, at around $11 to 12 billion.
Why does withdrawing from a Layer 2 take seven days?
On optimistic rollups, the challenge window exists so anyone can submit a fraud proof against an invalid batch. Bypassing the wait, third-party bridges introduce their own counterparty risk.
Is a sidechain the same as a Layer 2?
No. Running its own consensus and its own security makes a sidechain closer to a Layer 1. A true Layer 2 settles back to the base chain and inherits its security.
