Rollups, as the current mainstream Layer2 scaling solution, have contributed to Ethereum's pursuit of scalability. Both Optimistic Rollup and ZK Rollup have been gradually validated in the market. Following this, the Layer2 scaling space has witnessed the emergence of multiple Rollup directions, allowing anyone to quickly launch their own Rollup using an SDK and run applications on Rollup with high performance and low cost. In the future of Layer2 scaling, Rollups are expected to dominate, and the most important aspect is simplifying the deployment of various types of Rollups for developers.

On June 26th, zkSync launched ZK Stack, a modular open-source framework for building zk-rollup-based L2 and L3 (referred to as superchains). ZK Stack aims to provide a codebase for building customized ZK-supported Layer2 and Layer3 chains in the zkSync era. Prior to this, the Optimism team introduced the OP Stack, an extensibility solution to create new Layer2 blockchains, aiming to create a shared, high-quality, and fully open-source system.

In this article, we will compare the similarities, differences, advantages, and use cases of these two solutions. In the increasingly competitive Layer2 market, who will break through and create a larger ecosystem interoperability?

OP Stack: OP Stack is a standardized, shared, and open-source development stack maintained by the Optimism Collective to support Optimism. It consists of multiple software components and serves as the backbone of the Optimism ecosystem. OP Stack focuses on creating a shared, high-quality, and fully open-source system for building new Layer2 blockchains. By coordinating shared standards, Optimism Collective avoids duplicating the same software in isolation. OP Stack can be seen as software components that help define specific layers of the Optimism ecosystem and can also serve as modules within existing layers. While OP Stack's current core is the infrastructure for running Layer2 blockchains, it can theoretically expand to layers above the underlying blockchain, including block explorers, message passing mechanisms, governance systems, and other tools.

OP Stack divides the blockchain into three main layers: the consensus layer, execution layer, and settlement layer. These layers are standardized, and in terms of specific architecture, OP Stack can be divided into six layers:

1. Data Availability (DA) Layer: The data availability layer defines the source of raw data for Layer2 based on OP Stack. OP Stack can use one or more data availability modules to obtain its input data. Ethereum DA is currently the most widely used data availability module in the OP Stack, but more chains can be added in the future.

2. Sequencing Layer: The sequencing layer determines how user transactions on the OP Stack chain are collected and published to the data availability module in use. In OP Stack's default Rollup configuration, sequencing is typically handled by a single dedicated sequencer. Rules defined in the derived layer often restrict the sequencer's ability to retain transactions for a specific time period. In proposed futures, sequencing will be modular so that chains can easily choose and change the mechanism that controls their current sequencer.

3. Derivation Layer: The derivation layer defines how raw data from the data availability layer is processed to form processed inputs that are sent to the execution layer via the standard Ethereum engine API.

4. Execution Layer: The execution layer defines the state structure within the OP Stack system. The execution layer abstracts an EVM modification or a completely different underlying VM.

5. Settlement Layer: The settlement layer is responsible for verifying the current transaction results. After confirmation by Layer2, the confirmation information is sent to the target blockchain for final settlement and data availability.

6. Governance Layer: The governance layer refers to the general tools and processes used for managing system configuration, upgrades, and design decisions.

OP's goal is to upgrade to a superchain through this architecture. OP Stack deconstructs the components required to build Layer2 chains and packages them as separate modules, allowing developers to combine the most suitable modules to create their own Layer2 chains and simplify the implementation of proprietary chains.

Bedrock Upgrade:

The completion of the Bedrock upgrade represents a fully modular rewrite of the core components of the OP mainnet Rollup architecture. The first official version of OP Stack is launched, marking the next major version of the Optimism network and further narrowing the gap between Optimism and Layer1 Ethereum. Bedrock version will support multiple proof systems and multiple clients to attract different developers and projects. It will also follow different paths to pursue technical decentralization while maintaining decentralized governance. This provides a key advantage for OP to achieve a superchain in the future:

1. Reduced network fees: Optimization of data compression strategies eliminates Gas Fees related to EVM execution when submitting data to L1, reducing additional costs by approximately 10%.

2. Reduced deposit wait time: Support for Layer1 reorgs in node software is introduced, with deposits expected to be confirmed within 3 minutes.

3. Improved proof modularity: The proof system is abstracted separately from OP Stack, allowing a choice between fault-tolerant proofs or validity proof mechanisms such as ZK-Snarks.

4. Improved node performance: By executing multiple transactions in a single Rollup block, approximately 15GB of data volume can be reduced annually.

5. Improved Ethereum equivalence: Multiple deviations from Ethereum in previous versions are removed, and support for EIP-1559, chain reorgs, and other Ethereum features present on Layer1 is added.

After the Bedrock upgrade, Optimism's Layer2 Rollup is improved, and it further advances Optimism's upgrade to a superchain. The next major scalability improvement of OP Stack is introducing the concept of a superchain, which includes shared bridging, decentralized governance, upgrades, and communication layers. All of these are built on top of OP Stack. The launch of the superchain will merge the Optimism mainnet and other chains into a unified OP chain network, representing an important step towards scalable and decentralized computing.

OP Stack simplifies the process of creating Layer2 blockchains and supports all Optimism software. With the development of Optimism, OP Stack will continue to evolve. Coinbase is preparing to launch Base Layer2 this year, which will be based on OP Stack. BNB Chain has also announced the opBNB testnet, built on OP Stack. Currently, OP Stack appears as software behind the Optimism mainnet and will eventually emerge as the Optimism superchain and its governance.

ZK Stack: ZK Stack is a free, modular, open-source framework designed to build customized ZK-supported L2 and L3 (superchains) based on the zkSync era. The core of ZK Stack provides two key functionalities: sovereignty and seamless connectivity. Developers have full rights to the code and unrestricted autonomy to customize and shape every aspect of the chain. Superchains run independently, relying only on Ethereum Layer1 to ensure their liveness and security, while the superbridge network facilitates the interconnection of each superchain, enabling trustless, fast, and cost-effective interoperability. In summary, ZK Stack has three main features: open-source, composability, and modularity.

1. Free: ZK Stack is developed under fully permissive MIT/Apache open-source licenses, ensuring its availability for free.

2. Composability: Superchains built using ZK Stack can seamlessly connect in a trustless network with low latency and shared liquidity.

3. Modularity: Customize and shape every aspect of the superchain, from choosing sequencers and data availability modes to defining unique token economics.

4. Ultra-low cost: Due to the simplicity of ZK proofs, certain transaction types, such as oracle updates, can be 1,000 times cheaper on ZK Stack compared to other aggregation platforms. In addition to the ZK rollup mode, ZK Stack also enables affordable scalability with zkPorter accounts for appropriate use cases.

5. Proven: zkSync Era is the most widely adopted ZK rollup on Ethereum, with substantial TVL and transaction volume as proof. With this track record, ZK Stack is a secure choice in terms of security and reliability.

6. Future-oriented: ZK rollups are the future of Ethereum scalability. Building the right architecture from the beginning to fully leverage the superpowers of ZK.

Upgrade of ZK Stack:

The upgrade to ZK Stack is a significant milestone for the zkSync core team. Shifting from zkSync Era to ZK Stack, the team's perspective has gradually expanded from building ZK technology to helping numerous teams understand ZK Stack and contribute to it. With the launch of more superchains, the number of core contributors will increase, and the community will become the true owner of the zkSync network, especially when building custom superchains. If developing a general DeFi dapp or NFT project, deploying it on existing superchains like zkSync Era will be a simpler process, allowing synchronization and integration with other protocols in the ecosystem.

Furthermore, ZK Stack allows for the construction of sovereign superchains without sacrificing interoperability and composability. This greatly enhances the scalability of ZK Stack. Each superchain seamlessly integrates into its infinitely scalable ecosystem, supported by shared provers and fractal scaling, fostering a complete liquidity network. In this ecosystem, users can transfer assets quickly and trustlessly without incurring additional costs. Smart contracts will have cross-chain asynchronous calls, and the superchains themselves will have sovereignty, enabling them to join alternative ecosystems and withdraw their on-chain assets when choosing to leave.

Next, the ZK Stack team will make modifications to the codebase for easier checkout, configuration, and deployment of ZK Stack instances, ultimately achieving the goal of one-click deployment.

OP Stack vs ZK Stack: The introduction of ZK Stack represents not so much a competition with OP Stack but rather a new direction towards multi-chain interaction.

From a technical perspective, ZK Stack maximizes the reuse of Ethereum's security and consensus methods, directly relying on Ethereum's security. Compared to OP's fraud proofs for interaction, ZK proofs directly verify state changes without waiting for underlying Ethereum state transitions, simplifying the design and avoiding redundant investments, thereby improving inter-chain interaction efficiency. In contrast, OP Stack still has significant limitations in asynchronous cross-chain calls: state changes require waiting for Ethereum's underlying verification, and fraud proofs also require confirmation.

Furthermore, unlike OP Stack's focus on the transition to the Layer2 market, ZK Stack aims to encompass both the Layer2 and Layer3 markets. Although both aim to achieve a multi-chain empire through inter-chain interoperability, ZK Stack's construction of Layer3 and multi-chain networks seeks highly customizable scalability.

From an ecosystem perspective, OP Stack has an advantage as a first mover. Shortly after its launch, OP Stack gained support from many projects. In February of this year, Coinbase announced the launch of Base, a multi-chain Layer2 platform built on OP Stack, and plans to build a superchain together with Optimism Collective. Additionally, OP Stack has gained support from BNB Chain. On the evening of June 19th, BSC announced a new scaling solution, opBNB, based on OP Stack's Bedrock version and compatible with EVM. Moreover, many application development teams, such as the NFT marketplace Zora and a16z Crypto's client Magi, have started choosing OP Stack to develop application chains.

In comparison, zkSync's Layer2 is not yet fully established and has been experiencing compatibility and downtime issues with ZK Rollup. The ecosystem mainly consists of smaller projects, with limited support from well-known companies and projects. In this regard, zkSync's eagerness to build Layer3 has not convinced the market's acceptance.