What are ZK Rollups?
Summary
ZK-rollups are Layer 2 networks that execute transactions off Ethereum and submit cryptographic validity proofs so incorrect state changes are impossible. This article explains how ZK-rollups use blobs for data availability, achieve proof-driven finality in minutes, and scale further with zkEVMs, compression, and recursive proofs.
ZK-rollups are Layer 2 scaling systems that execute transactions off Ethereum and use cryptographic validity proofs to guarantee correctness—making invalid state transitions mathematically impossible rather than merely punishable. This proof-driven model removes the need for challenge periods, delivering near-instant finality while preserving Ethereum’s security guarantees.
In this article, you’ll learn how ZK-rollups anchor security to Ethereum through data availability and on-chain proof verification, how components like sequencers, provers, Merkle state roots, and zkEVMs work together, and why ZK-rollups are increasingly favored for high-value DeFi and institutional use cases in the modular Ethereum landscape of 2026.
How do ZK-Rollups Interact with Ethereum?
The interaction between a ZK-rollup and the Ethereum Mainnet (Layer 1) is governed by rigorous cryptographic verification rather than the "trust-but-verify" model of optimistic rollups.
Data Availability
For a ZK-rollup to function, it must post enough data to L1 for any observer to reconstruct the state. In 2026, this is primarily achieved through EIP-4844 Blobs.
- Ephemeral Storage: Unlike standard transactions, blobs are stored for approximately 18 days before being pruned by Ethereum nodes.
- Efficiency Advantage: ZK-rollups are significantly more efficient with blob space than optimistic rollups. While optimistic designs must post the entire transaction data, ZK-rollups only need to post state diffs (the "before and after" changes) or highly compressed transaction data, because the validity proof itself confirms that the changes are correct without needing to re-execute every step.
Transaction Finality
ZK-rollups offer "Proof-Driven Finality." Unlike optimistic rollups that wait seven days for a challenge window to expire, a ZK-rollup achieves hard finality on Ethereum as soon as its validity proof is verified by the on-chain L1 contract. This typically occurs within 15 to 60 minutes, depending on the prover's batching strategy and L1 gas costs. Once the proof is accepted, the transaction is as irreversible as an L1 Ethereum block.
Censorship Resistance
To prevent sequencers from blocking transactions, ZK-rollups implement Forced Inclusion and Escape Hatches:
- Forced Queue: Users can bypass a malicious sequencer by submitting a transaction directly to the L1 "Forced Queue" contract.
- Emergency Exit: If the rollup operator goes offline, users can provide a Merkle proof of their account state to the L1 contract and withdraw their assets directly, ensuring that funds are never "trapped" in the Layer 2.
How do ZK-Rollups Work?
The operational cycle of a ZK-rollup transforms thousands of off-chain actions into a single, compact proof.
Transactions
- Users submit transactions to the rollup's mempool.
- A Sequencer orders these transactions and executes them against the current off-chain state.
- A Prover then takes the execution trace and generates a mathematical proof (SNARK or STARK) that the state transition followed all protocol rules.
State Commitments
The rollup state is maintained as a Merkle Tree. Each time a batch is processed, the sequencer computes a new State Root. This root is submitted to the L1 along with the proof. The L1 contract stores this root as the "canonical" state of the rollup, serving as the source of truth for all subsequent interactions.
Validity Proofs
There are two primary types of validity proofs used in 2026:
- zk-SNARKs: Used by zkSync and Scroll. They are extremely compact (hundreds of bytes) and cheap to verify on-chain, but they often require a "trusted setup" and are computationally intensive to generate.
- zk-STARKs: Used by Starknet. They are larger but faster to generate, require no trusted setup, and are "post-quantum secure," meaning they are resilient to potential attacks from future quantum computers.
Entries and Exits
- Deposits: A user locks assets in an L1 bridge contract. The rollup detects this event and mints a corresponding "wrapped" asset on the L2.
- Withdrawals: The user "burns" assets on the L2. A proof of this burn is included in the next batch proof. Once verified on L1, the assets are instantly unlocked for the user on the Mainnet.
ZK-Rollups and EVM Compatibility
The most significant advancement in 2025–2026 has been the maturation of the zkEVM, which allows developers to run Ethereum smart contracts without modification in a ZK-proven environment. Vitalik Buterin’s classification system defines four types:
- Type 1 (Fully Ethereum-Equivalent): Mirrors Ethereum exactly, including hash functions. These are "perfect" but generate proofs very slowly.
- Type 2 (Fully EVM-Equivalent): Retains compatibility for developers but changes internal storage structures to make proof generation faster. Examples: Scroll, Polygon zkEVM.
- Type 3 (Almost EVM-Equivalent): Omit certain precompiles that are difficult to prove. Most Type 2s start as Type 3.
- Type 4 (High-Level-Language Equivalent): Compiles Solidity into a custom, ZK-optimized language. These are the fastest to prove but have the highest friction for moving existing code. Example: Starknet (via Cairo).
How do ZK-Rollups Scale Ethereum?
ZK-rollups achieve massive scaling by reducing the data footprint of every transaction and using hierarchical verification.
Transaction Data Compression
On Ethereum L1, a transaction requires ~110 bytes. In a ZK-rollup, this is reduced to ~12 bytes. This is largely due to Signature Aggregation: instead of posting thousands of individual ECDSA signatures (each 68 bytes), the rollup posts a single validity proof that mathematically confirms all signatures in the batch were valid.
Recursive Proofs
ZK-rollups utilize Proof Recursion, where a single validity proof can verify the correctness of other validity proofs. This enables:
- Fractal Scaling: Creating Layer 3 (L3) networks that settle to the L2, which in turn settles to the L1. This allows for specialized chains (e.g., for gaming or high-frequency trading) with near-zero costs.
- Parallel Proving: Breaking a massive batch of 100,000 transactions into 10 smaller batches, proving them simultaneously, and then merging those proofs into one final summary for Ethereum.
Pros and Cons of ZK-Rollups
| Pros | Cons |
| Instant Finality: No 7-day withdrawal delay. | Computational Overhead: Generating proofs requires high-end hardware. |
| Superior Security: Math-based guarantees vs economic assumptions. | Prover Centralization: Proof generation is often limited to specialized nodes. |
| Better Privacy: Potential for "shielded" transactions. | Complexity: Harder to build and maintain than optimistic models. |
A Visual Explanation of ZK-Rollups
Imagine a math teacher (Ethereum) and a student (the Rollup).
- Monolithic L1: The student shows the teacher every single step of 1,000 long-division problems. The teacher has to re-calculate everything to grade it.
- ZK-Rollup: The student solves 1,000 problems and provides only the final answers plus a single mathematical formula that could only be solved if every one of the 1,000 answers was correct. The teacher (Ethereum) only has to check the one formula to know the entire page is perfect.
Work cited
- EIP-4844: Ethereum's Protodanksharding - QuillAudits
- Fault proof VM: Cannon - Optimism Docs
- How EIP-4844 Changed Ethereum Gas Prices - DEV Community
- EIP-4844: Blob Transactions and the First Step Toward Data Sharding - Medium
- Inside Arbitrum - Offchain Labs Dev Center
- Optimistic Rollups vs ZK Rollups in 2026: Which Layer-2 Should You Build On? - Codezeros
- What is Fraud Proof? Definition, How It Works, Benefits & Risks | Cube Exchange
- What is Layer 2 Blockchain? How L2 rollups scale Ethereum - Cube Exchange
- How Do Censorship-Resistant Transactions Work in Ethereum Rollups - Gate.com
- Cost Optimization in Layer 2 Rollups via EIP‐4844: A Gas Efficiency and Economic Analysis
FAQ
A ZK-rollup is a Layer 2 network that executes transactions off Ethereum and submits cryptographic validity proofs, making invalid state changes mathematically impossible.
