Understanding the OP Stack

The Optimism Network is built on top of a base referred to as the Over Powered Stack, OP Stack or opstack, hence the moniker of its current iteration; Bedrock. Providing a deployable foundation for the construction of optimistic rollup networks, the OP Stack acts as a concrete slab upon which custom architectures can be built. Within this role, it is speculated that the OP Stack will provide the requisite infrastructure for the development of an interoperable ecosystem of rollup networks dubbed the Superchain. As a public good for Ethereum and Optimism, the OP Stack is a changing concept that may grow to suit the needs of this evolving ecosystem. With the principles of decentralisation and scalability at its core, the eventual size and scope of the OP Stack may extend far beyond that of present blockchain ecosystems. 

What Is Optimism?

Optimism is a layer 2 scaling solution built on top of the Ethereum mainnet that aims to improve the performance, scalability, and cost-effectiveness of transactions on the blockchain. It is designed to offload a portion of the burden of execution from the mainnet to its own network while remaining integrated with the Ethereum ecosystem. Optimism provides faster transactions and reduces gas fees by executing them on their own network as well as using advanced data compression techniques. These improvements have enabled Optimism to achieve average gas savings as low as 0.8% of Ethereum. 

Optimism achieves its own implementation of rollup technology. Optimism itself exists as a smart contract on the Ethereum mainnet – referred to as the rollup operator. This contract serves as a gateway between the mainnet and the rollup itself, which is a separate network that processes transactions off-chain. When a user submits a transaction on the rollup network, it is recorded by the rollup along with all other pending transactions. The transactions are then rolled up into a batch and submitted along with the proof to the rollup contract on the mainnet that verifies the proof and executes the transactions on the base layer. There are two different types of rollups, differentiated by the type of proof they use; the optimistic rollup and the zero-knowledge rollup. Optimism, as the name suggests is an optimistic rollup, meaning that transactions are assumed to be innocent until proven guilty. Before the batch of transactions is finalised on the base layer a challenge period occurs, during which any network participant can analyse the batch for fraud and if it is encountered, generate a fraud-proof. 

Optimism itself is the second-largest rollup currently operating on Ethereum, the centre of the present rollup landscape. Measured by Total Value Locked (TVL), Optimism is second only to Arbitrum with roughly US $2 billion and US $1 billion TVL respectively at the time of writing. The two networks are rapidly growing, even surpassing Ethereum in terms of combined daily transactions. As a result, the Optimism network hosts a growing ecosystem of DApps comparable in size to that of notable layer 1’s such as Avalanche. With Ethereum’s ‘rollup centric roadmap’, the Optimism network is expected to continue its growth trajectory and remain a leading player in the rollup ecosystem. To ensure this, the platform is expanding its OP Stack to allow for a horizontally scalable, interoperable ecosystem of OP Stack-based networks. 

What is the OP Stack?

Powering the Optimism network and its ecosystem, the OP stack – also known as optimism stack – is a collection of software components that currently makes up the infrastructure of the Optimism mainnet. Maintained by the Optimism Collective, Optimism’s large and well-funded community, the OP Stack defines the modules within the Optimism stack. According to the Optimism team, these modules are included or excluded with the principles of utility, simplicity and extensibility in mind. A new module must help to power the Optimism Collective, be simple and understandable to enable scalability and reduce engineering costs as well extensible to ensure that the module can be used to be built with and on top of. The software for the stack itself is decentralised and open source, meaning that any user can access and contribute to the codebase.

The primary focus of the OP Stack is to create a shared, high-quality, and fully open-source system for deploying new rollup networks. This is particularly important with the advent of the Superchain concept, which requires the secure creation of new networks that can interoperate within the proposed Superchain ecosystem. By coordinating on shared standards, the Optimism Collective can avoid rebuilding the same software in silos repeatedly. While the OP Stack currently simplifies the process of creating layer 2 blockchains, it is not limited to this. The OP Stack extends to layers on top of the underlying blockchain, including tools like block explorers, message-passing mechanisms, governance systems, and more.

Presently, the OP Stack is operating on its Bedrock iteration, the first deployment of the stack. Bedrock provides the tools for launching optimistic rollup networks, with the setup of its APIs specifically designed to support the said rollups. This release was built to support the Optimism Superchain, a proposed network of layer 2s that share security, communication layers, and a common development stack (the OP Stack itself). Bedrock enables developers to quickly create and deploy a custom rollup network compatible with the Superchain ecosystem. However, as of the Bedrock release, the OP Stack is not designed to support modifications, an important quality for the customisation of rollup networks that will be necessary for the advent of future iterations of the OP Stack. 

Structure of the OP Stack

Presently, Ethereum serves as the dedicated DA layer for the OP Stack. Inputs from the sequencer module are formatted and published directly to Ethereum. As the base layer of the network, the integrity of the OP Stack is contingent on the security of the data stored on Ethereum. Being that data on Ethereum is stored on its blockchain, the security of said data is ensured via its Proof of Stake (PoS) consensus mechanism. As a DA layer, Ethereum does not only store data but also offers assurances that all blocks are completely accessible to network participants. On the Ethereum network, these assurances are provided by network participants that download and verify the contents of individual blocks. Post-completion of Ethereum’s rollup-centric roadmap the DA layer is expected to begin relying on the data structures and DA assurances outlined in EIP-4844 such as Binary Large Objects (BLOBs) and Data Availability Sampling (DAS). 

The OP Stack currently relies on a single Optimism sequencer module that collects and publishes transaction data from the execution layer to the DA layer. This sequencer is responsible for confirming valid transactions, creating batches and submitting them to the base layer, forming the core of the rollup itself. As a part of their vision for a decentralised rollup network, Optimism plans to introduce a sequencer set. This modular sequencer set will better prepare the OP Stack for the introduction of multiple rollup networks to be built using it. Using the sequencer set, OP Stack-based chains can circumvent the development of their own sequencer and access atomic cross-chain composability with other chains. 

In order to process transactions and execute state changes, the Ethereum Virtual Machine (EVM) makes up the dedicated module for the OP Stack execution layer. This module processes inputs from the derivation layer and uses them to create state writes for state transitions. Given that the OP Stack implementation of the EVM is merely lightly modified to support layer 2 transactions initiated on Ethereum, the state structure of OP Stack-based chains is completely composable with that of all other EVM-based protocols. This enables seamless redeployment of smart contracts onto OP Stack-based chains, significantly expediting the development of native ecosystems. 

To derive data inputs for the creation of state writes, the execution layer relies on the derivation layer. The derivation layer determines how raw data from the DA layer is formatted and processed to form the inputs for the execution layer. It does so by using a rollup module that derives inputs filtered through the Ethereum Engine API from block data, sequencer batches, transaction events, etc. This rollup module is expected to be replaced with a proposed indexer module that would execute the same functionality when events occur on specified smart contracts existing on the base layer. 

The settlement layer is a read-only mechanism for external blockchains that enables third-party chains as well as OP Stack chains to become aware of the state of an OP Stack chain and execute decisions based on such. Presently, settlement is established via an attestation-based fault-proof mechanism, in essence utilising optimistic fraud proofs. Proposer entities can propose what they believe to be the current valid state of the OP Stack chain and if this state is not refuted using fraud-proof during the challenge period then the state is assumed to be valid. Fault-proof optimistic settlement is a proposed settlement module analogous to attestation-based fault proof with a permissionless fault-proving process rather than a multi-signatory challenger. Similarly, validity proof settlement is another proposed settlement module analogous to zero-knowledge proofs. 

Lastly, the governance layer consists of a set of modules used to manage the OP Stack. This layer is responsible for system configuration, upgrades and design decisions. Governance tokens and multi-signatory smart contracts are responsible for governance. Governance tokens are used to represent voting power in decentralised governance models such as DAOs. Similarly, multisig smart contracts are used to carry out decisions, particularly upgrades, upon receiving a threshold of signatures from a predefined set of participants. Often, decision-making using multisig smart contracts is prompted by votes carried out using governance tokens. 

The OP Stack presently powers the Optimism network. Its layered architecture provides an effective framework for the construction of secure, scalable and integrated rollup networks. Each layer is responsible for a necessary function and is carried out by a specific network or component. Together, they provide the requisite functionality to build a complete rollup network integrated within an interoperable OP Stack-based ecosystem. 

Source: Optimism Docs

Management Of The OP Stack

Aiming to be decentralised in nature, the OP Stack is managed by the Optimism Collective, a large-scale experiment in digital democratic governance. Stewarded by the newly formed Optimism Foundation, the Optimism Collective is built to drive rapid and sustainable growth of Optimism’s decentralised ecosystem. It operates under the ethos that humans are greater than capital, and impact equals profit. The governance of the collective will be equally divided between the Citizens’ House and the Token House. Token holders will be able to vote on protocol upgrades and project incentives through the Token House, while the Citizens’ House will facilitate the distribution of public goods funding generated from the revenue collected by the network. Via these mechanisms, the Optimism Foundation is intended to serve as a steward of the Optimism Collective, running transient governance experiments on behalf of the Collective and bootstrapping the ecosystem before eventually dissolving. 

One of the primary responsibilities of the Optimism Collective and by extension the Optimism Foundation is to contribute to the OP Stack. The codebase itself is managed by a group of developers who are committed to modifying it in accordance with the principles of utility, simplicity and extensibility. However, as a decentralised development stack, contributions are accepted from anyone assuming the component aligns with the aforementioned principles. These contributions are not limited to extra modules but include DApps, new protocols, bug hunts, documentation editing, content creation and several other areas vital to the development of the OP Stack. By democratising contributions to the stack, Optimism can leverage the expertise of its community members, significantly expediting the development of OP Stack modules and diversifying the scope of contributors beyond those of a small development team. 

The OP Superchain

In the rapidly evolving world of blockchain technology, the development of new and innovative solutions to long-standing problems has become a key focus for many organisations. The OP Stack is an essential component of the Optimism ecosystem providing a comprehensive framework for the deployment of rollup networks. Given that these rollup networks rely on the same infrastructure a high degree of interoperability can be achieved enabling an interconnected web of layer 2s referred to as the Superchain. 

What Is The OP Superchain And What Possibilities Does It Enable?

The Superchain is a proposed network of rollup networks within the Optimism ecosystem that share a common codebase the OP Stack. This structure is intended to provide an interoperable environment for different layer 2 networks to communicate and transact with one another, similar to the way the internet enables computers and devices to communicate. By leveraging the power of layer 2 solutions and a shared development stack, the Superchain can offer unprecedented levels of scalability and flexibility, allowing developers to create complex and interconnected decentralised applications that can seamlessly interact with one another.

Intended to provide a framework for horizontal scalability, the Superchain aims to solve several of the issues associated with traditional multi-chain architectures. These problems include differentiated security architectures between parallel chains resulting in compounded systemic risk as more chains are added to the network as well as the cost of each additional chain creating a new set of nodes. The Superchain solves these issues by enabling horizontal scaling without creating additional blockchains. Instead, new layer 2 networks are built on an analogous base layer that enables homogenous security and relies on the same sequencer set, thus solving the problems associated with multi-chain architectures. 

Structure Of The OP Superchain

‘OP chain’ is the moniker for individual chains existing on the Optimism Superchain. Unlike multi-chain designs, OP chains are built with a standardised architecture. This architecture consists of a shared base layer for DA, a shared bridge between the base layer and OP chains to ensure standardisation of security, a cheap and flexible framework for the deployment of the OP chains themselves, the OP chains and a cross-chain messaging protocol for the transfer of data and digital assets between OP chains. These features enable the total ordering of transactions across all OP Chains, enabling developers to leverage this property to create applications that target the Superchain as a whole, abstracting away the underlying chains on which the apps are running. In doing so, the Superchain provides an ideal platform for developing decentralised applications that target multiple networks.

The Path To Creating The OP Superchain

Upgrading Optimism to become a superchain necessitates the implementation of several changes intended to create an initial basis for the superchain, upon which OP chains can be built. Foremost among these changes is upgrading the Optimism bridge included in the Bedrock OP Stack iteration to become an OP chain factory capable of deriving data from OP chains. Furthermore, the multisig attestation-based fault-proof mechanism must be upgraded to a permissionless fault-proof optimistic fraud-proof mechanism. Lastly, multiple sequencers must be implemented to enable configurable sequencers for OP chains.

These upgrades will enable the creation of a more scalable and decentralised Optimism architecture. Nevertheless, in addition to the implementation of the aforementioned features, several problems with the Optimism Network and the OP stack itself must be addressed before realising this vision. These include issues with withdrawal claims, slow cross-chain transactions, asynchronous cross-chain transactions, and lack of scalability. To address these issues, potential future enhancements have been proposed such as multi-proof security to replace the present trusted set of chain attestors, upgraded message passing between layer 2s to ensure low latency, ensuring cross-chain transactions are synchronous and an alternative DA layer to Ethereum, with the proposed solution being a custom Plasma protocol. These enhancements, when combined, could enable the development of decentralised alternatives to even the most complex web2 applications.

Conclusion

In essence, understanding the OP Stack, or optimism stack, is crucial for grasping the future trajectory of the Optimism ecosystem. Hosting a novel mechanism for horizontal scaling, the OP Stack provides a new avenue for the expansion of the Optimism ecosystem. Being decentralised and open-source, the stack enables any member of the community to contribute to the codebase or use it for their own projects. By providing an attractive framework for the development of rollup networks, the OP Stack may give rise to a diverse and varied ecosystem of interoperable layer 2 chains. As such, the OP Stack has the potential to transform the Optimism landscape from a monolithic structure containing its own internal community to a bustling metropolis of individual chains, interacting with one another over a shared infrastructure. 

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FAQs

What is the Over Powered Stack (OP Stack) in the Optimism Network?

The Over Powered Stack, or OP Stack, is the foundation upon which the Optimism Network is built. It provides a deployable base for the construction of optimistic rollup networks, acting as a platform upon which custom architectures can be built. The OP Stack is speculated to provide the necessary infrastructure for the development of an interoperable ecosystem of rollup networks, referred to as the Superchain.

What is Optimism and how does it function?

Optimism is a layer 2 scaling solution built on top of the Ethereum mainnet. It aims to improve the performance, scalability, and cost-effectiveness of transactions on the blockchain. Optimism offloads a portion of the execution burden from the mainnet to its own network while remaining integrated with the Ethereum ecosystem. It achieves this by executing transactions on its own network and using advanced data compression techniques, leading to faster transactions and reduced gas fees.

What is the structure of the OP Stack?

The OP Stack is a collection of software components that make up the infrastructure of the Optimism mainnet. It includes modules that are included or excluded based on principles of utility, simplicity, and extensibility. The software for the stack is decentralized and open-source, meaning that any user can access and contribute to the codebase. The OP Stack focuses on creating a shared, high-quality, and fully open-source system for deploying new rollup networks.

What is the OP Superchain concept in the Optimism Network?

The Superchain is a proposed network of rollup networks within the Optimism ecosystem that share a common codebase, the OP Stack. This structure is intended to provide an interoperable environment for different layer 2 networks to communicate and transact with one another. The Superchain can offer unprecedented levels of scalability and flexibility, allowing developers to create complex and interconnected decentralized applications that can seamlessly interact with one another.

How is the OP Stack managed?

The OP Stack is managed by the Optimism Collective, a large-scale experiment in digital democratic governance. The Optimism Collective is built to drive the rapid and sustainable growth of Optimism’s decentralized ecosystem. It operates under the ethos that humans are greater than capital, and impact equals profit. The governance of the collective is equally divided between the Citizens’ House and the Token House. Token holders can vote on protocol upgrades and project incentives through the Token House, while the Citizens’ House facilitates the distribution of public goods funding generated from the revenue collected by the network.

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