The total value locked (TVL) in the zkSync network has surged past $140 million, marking a 38% increase within just one week. As an Ethereum Layer 2 scaling solution built on ZK Rollup technology, zkSync currently leads major Layer 2 networks in TVL growth. This trend highlights increasing adoption by users and capital flowing into the zkSync ecosystem and its applications.
Before Ethereum’s full transition to Ethereum 2.0, Layer 2 networks serve as a critical method for reducing on-chain congestion. By offloading transactional computation and storage from the mainnet, these networks help increase Ethereum’s scalability without compromising security.
Among various Layer 2 construction technologies, Rollup has emerged as a leading solution. It enables smart contracts to execute off-chain while bundling and compressing transaction data before submitting it to the Ethereum mainnet. This eliminates the need for individual transaction verification. As a result, Layer 2 networks secured by Rollup technology inherit Ethereum’s decentralization and security while boosting efficiency and scalability. Moreover, Rollup allows seamless migration of mainnet applications to Layer 2.
Different cryptographic verification methods within Rollup have led to multiple implementations, with Optimistic Rollup, ZK Rollup, and Arbitrum Rollup being the most prominent. Each approach has seen substantial development and real-world adoption.
ZK Rollup, which utilizes zero-knowledge proof verification, has been referred to by Ethereum co-founder Vitalik Buterin as the ultimate scaling solution for Ethereum Layer 2.
The recent spike in zkSync’s TVL underscores the viability of ZK Rollup technology. Since the public testnet launch of zkSync 2.0 in February, interest in ZK Rollup has grown considerably within the blockchain community.
So what exactly is ZK Rollup? How does it differ from Optimistic and Arbitrum Rollups? And besides zkSync, what other platforms are leveraging ZK Rollup technology? This article breaks down these questions and more.
What Is ZK Rollup?
The Basics
ZK Rollup is a Layer 2 scaling solution that uses zero-knowledge proofs (ZK) to verify transactions off-chain. The concept originated in late 2018, introduced by blockchain researcher Barry Whitehat.
Like all Rollups, ZK Rollup processes complex computations off-chain, generates a cryptographic proof, and submits this proof to the mainnet for verification. A small amount of data is stored on-chain to ensure data availability, all while maintaining the security guarantees of Ethereum.
The core innovation lies in its use of zero-knowledge proofs. This cryptographic method allows a prover to demonstrate the validity of a statement without revealing any underlying information.
For example, suppose Alice wants to prove to Bob that she possesses a key to a specific room without showing the key. She can enter the room and retrieve an object that Bob knows is inside, thereby proving she has access—without ever revealing the key itself.
This privacy-preserving feature has made zero-knowledge proof technology essential in blockchain, with roots in Bitcoin. Beyond privacy, ZK proofs improve performance by allowing one entity to generate a proof that others can quickly verify, avoiding the need for every node to recompute complex transactions.
In ZK Rollup, multiple transactions are bundled off-chain, and a single zero-knowledge proof is generated. Mainnet validators then verify this proof almost instantly. This allows for immediate finality and fast asset withdrawal back to Layer 1.
How ZK Rollup Compares to Other Rollup Solutions
ZK Rollup and Optimistic Rollup are the two major Rollup approaches, differentiated primarily by their verification mechanisms.
Optimistic Rollup uses fraud proofs. Validators must stake ETH as collateral to participate. The system assumes all transactions are valid unless challenged. If a dispute arises, the contested transaction is verified on the mainnet. Malicious validators lose their stake. This design introduces a 7-day challenge period for withdrawals, delaying user access to funds and creating a suboptimal user experience.
Moreover, if fraud is suspected, all transactions in a batch must be re-verified on-chain, increasing the load on Ethereum.
Arbitrum Rollup improves on this by isolating only the disputed part of a transaction batch, reducing the burden on the mainnet. It also achieves full compatibility with the Ethereum Virtual Machine (EVM), allowing easy migration of dApps from Ethereum. Many DeFi protocols have launched Arbitrum versions as a result.
Still, Arbitrum requires a waiting period for withdrawals, a lingering drawback.
ZK Rollup had also struggled with EVM compatibility. Vitalik Buterin once stated that full compatibility might take years due to technical complexity. He suggested Optimistic Rollup would dominate short-term, with ZK Rollup being the long-term ideal.
Surprisingly, ZK Rollup development accelerated faster than expected. zkSync 2.0 introduced a public testnet with EVM compatibility in February, marking a turning point for practical ZK Rollup adoption.
Today, the main implementations of ZK Rollup are developed by StarkWare and zkSync.
zkSync’s Journey to EVM Compatibility
The Matter Labs team began developing zkSync in 2019. zkSync 1.0 launched in June 2020, focusing primarily on payments. It offered extremely low transaction fees, fast processing, and support for ETH and ERC-20 tokens as gas payment. Withdrawals to mainnet took minutes to hours.
Although zkSync 1.0 was not EVM-compatible—limiting its use cases—it became popular for low-cost, instant transfers.
The release of zkSync 2.0’s public testnet in February was a milestone. It introduced EVM compatibility, making it the first ZK Rollup network to support Ethereum-native smart contracts. Developers can now write in Solidity and deploy dApps with minimal changes, and users can interact with them at low cost and high speed.
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Notable Applications on zkSync
ZigZag Exchange
ZigZag is a decentralized exchange (DEX) that uses an order book model instead of the typical automated market maker (AMM) system. Leveraging ZK Rollup’s capabilities, it offers low-slipage trading with high liquidity, positioning itself as a chain-native alternative to centralized exchanges.
Orbiter Finance
Orbiter Finance is a cross-chain bridge supporting asset transfers between zkSync, Arbitrum, Optimism, and other Layer 2 networks, as well as between Layer 2 and Ethereum mainnet.
StarkWare’s Ecosystem Approach
StarkWare, founded in 2018, offers a comprehensive suite of Layer 2 products. It developed zkSTARK, a novel proof system that enhances scalability, and built two main products: StarkNet and StarkEx.
StarkNet
StarkNet is a decentralized ZK Rollup network on Ethereum. Its testnet launched in November 2021, allowing developers to deploy smart contracts and users to submit transactions. Batches of transactions are proven using STARK proofs and verified on Ethereum with minimal computational overhead.
While StarkNet does not yet support EVM compatibility, it already hosts dApps like the DEXs MySwap and JediSwap.
StarkEx
StarkEx is a scalable engine designed to help Ethereum applications scale. It is already integrated into major dApps:
- dYdX: A perpetual futures trading platform that uses StarkEx for high-speed settlements and improved user experience.
- DeversiFi: The first DEX to use StarkEx. It employs an order book model with off-chain execution and on-chain settlement, offering instant trades, high liquidity, and privacy via zkSTARK.
- Immutable X: An NFT-focused Layer 2 that enables gas-free, instant NFT trading and withdrawals. Popular Web3 games like Gods Unchained and Illuvium are built on it.
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Frequently Asked Questions
What is ZK Rollup?
ZK Rollup is a Layer 2 scaling technology that processes transactions off-chain using zero-knowledge proofs. It batches transactions and submits a single proof to the mainnet, ensuring security and rapid finality.
How does ZK Rollup differ from Optimistic Rollup?
While Optimistic Rollup relies on fraud proofs and a 7-day challenge period, ZK Rollup uses validity proofs, enabling instant withdrawals and better efficiency without trust assumptions.
Is zkSync compatible with Ethereum smart contracts?
Yes, zkSync 2.0 supports EVM compatibility, allowing developers to port Ethereum dApps with minimal changes and users to interact with them at low cost.
What are the benefits of ZK Rollup?
Key benefits include near-instant finality, lower transaction costs, enhanced scalability, and a smooth user experience—without compromising on security.
Which major projects use ZK Rollup?
zkSync and StarkWare are the two biggest players. Projects like ZigZag, dYdX, and Immutable X use ZK Rollup technology for scaling.
Can users withdraw assets instantly from ZK Rollup?
Yes, one major advantage of ZK Rollup is instant withdrawals to Ethereum mainnet, unlike Optimistic Rollup solutions which impose a waiting period.