X Layer Architecture Migration: From Polygon zkEVM to OP Stack
X Layer Architecture Migration: From Polygon zkEVM to OP Stack> This article provides a technical deep dive into X Layer's migration from Polygon CDK (zkEVM Validium) to the OP Stack, covering architectural changes, migration rationale, technical comparison, and impact on developers.
Background
X Layer is an Ethereum Layer 2 network launched by OKX, using OKB as its gas token. When the mainnet officially launched on March 30, 2024, X Layer adopted Polygon zkEVM as its underlying technology stack, built on a zkEVM Validium architecture that leverages zero-knowledge proofs to verify transaction validity while storing transaction data off-chain to reduce costs. In its early days, Polygon zkEVM provided X Layer with the ability to bootstrap quickly, enabling the rapid construction of an EVM-compatible Layer 2 network.As the network continued to operate and its ecosystem evolved, on October 27, 2025, OKX made a significant technical decision — to migrate the X Layer from Polygon zkEVM to Optimism's OP Stack. This means X Layer's underlying architecture shifted from a zero-knowledge proof-driven Validity Rollup to a fraud proof-driven Optimistic Rollup.
Technical Comparison of the Two Architectures
1. Core Verification Mechanism
Polygon CDK (zkEVM Validium) uses zero-knowledge proofs (ZK Proofs) as its core security mechanism. After each batch of transactions is executed on L2, the Prover node generates a cryptographic proof (Validity Proof) and submits it to a verification contract on Ethereum L1. Once the proof is verified, the state transition is confirmed as valid and immutable.OP Stack (Optimistic Rollup) employs a fraud proof mechanism. Transactions submitted to L1 are assumed valid by default, with a challenge window (typically 7 days) during which anyone can submit fraud proof to dispute an invalid state transition. If no challenge is raised, the state is finalized.
2. Data Availability
Polygon CDK's Validium mode stores transaction data off-chain, submitting only ZK proofs and state roots to L1. This significantly reduces L1 data publishing costs but introduces a dependency on a Data Availability Committee (DAC).OP Stack's standard configuration publishes transaction data as calldata or blobs to Ethereum L1 (using blobs post EIP-4844), ensuring data availability is secured by Ethereum's consensus layer without additional trust assumptions.
3. EVM Compatibility
zkEVM requires implementing EVM opcodes within zero-knowledge proof circuits, and certain advanced opcodes (such as SELFDESTRUCT and some precompiled contracts) may have compatibility differences or limitations.OP Stack is built on a modified version of Geth (op-geth), making it nearly EVM Equivalent. Developers can directly migrate contracts and toolchains from Ethereum L1 without any modifications.
4. Ecosystem and Interoperability
Polygon CDK connects to AggLayer, enabling cross-chain interoperability between Polygon CDK chains. AggLayer achieves unified security and shared liquidity through aggregated proofs.OP Stack has a broad L2 ecosystem, currently handling approximately 70% of Ethereum L2 transaction activity, with more mature developer tooling and middleware support. After migration, X Layer adopts the OP Stack as its foundational infrastructure while operating as an independent L2, maintaining its own network governance and operational autonomy.
Reasons for Migration
1. Ecosystem Scale
OP Stack is the most widely deployed L2 framework, powering approximately 70% of Ethereum L2 activity and around 12% of daily crypto transactions. A large number of industry-leading projects are built on the OP Stack, with more comprehensive developer tooling and middleware support.
2. Developer Experience
OP Stack's EVM equivalence translates to better toolchain compatibility — Hardhat, Foundry, Ethers.js, and other development tools work seamlessly. While zkEVM continues to improve, compatibility issues may still arise in certain edge cases.
3. Upgrade Cadence
The OP Stack is continuously maintained by the Optimism team, with frequent upgrades and strong backward compatibility. Polygon CDK underwent significant strategic changes in 2025 (with the announced sunset of Polygon zkEVM Mainnet Beta), creating uncertainty in its ecosystem direction.
Impact on Developers
Smart Contract
For most Solidity contracts, the migration impact is minimal. OP Stack's EVM equivalence means contracts previously deployed on X Layer can typically run directly on the new architecture. Key points to note:
L1 <> L2 messaging interfaces have changed (from Polygon zkEVM Bridge to a new bridging solution)
Cross-chain message confirmation has shifted from ZK proof-based instant confirmation to a fraud proof challenge window
Infrastructure
RPC Endpoints: Node software has switched from Erigon-based to op-geth; RPC interfaces remain compatible with the Ethereum standard JSON-RPC specification
Block Structure: Minor differences in block header format and transaction receipt structure
Timeline
Date | Event |
March 30, 2024 | X Layer mainnet launch, built on Polygon zkEVM (Validium) |
October 27, 2025 | X Layer migration from Polygon zkEVM to OP Stack |
Conclusion
The migration from Polygon zkEVM to the OP Stack represents a significant upgrade in X Layer's technical evolution. After thorough evaluation of ecosystem maturity, developer experience, and long-term maintainability, we chose the OP Stack as our new underlying architecture to deliver a more stable and efficient Layer 2 experience for developers and users.With the migration complete, X Layer offers stronger EVM equivalence and more comprehensive toolchain support, enabling developers to build and deploy applications at lower cost. We will continue to optimize network performance, enhance developer documentation and migration guides, and ensure that ecosystem partners and community developers can transition smoothly to the new architecture.Follow X Layer's official channels for the latest updates, and we look forward to building the next generation of on-chain applications together with more developers on X Layer.