A few months ago, the Avail team released the OpEVM, an SDK to allow anyone to build their own sovereign optimistic rollup with working fraud proofs, shared sequencer support, permissionless watchtowers, and much more.
Context
The OpEVM SDK is a promising alternative to traditional smart contract-based rollups. Developers can use the OpEVM SDK to build sovereign, EVM-compatible optimistic rollups. This tech provides developers with a decentralized infrastructure for running a layer-2 (L2) blockchain, that can support a decentralized sequencer set, exists without an enshrined bridge on a layer-1 (L1), and genuinely verifies state transitions optimistically.
OpEVM is built to work atop Avail’s DA Layer, but can also be used to work on any chain - even Bitcoin. One of the unique features of the OpEVM is its ability to facilitate dispute resolution independent of smart contracts.
The OpEVM SDK allows anyone to spin up their own sovereign optimistic rollup and begin experimenting with the construct relatively quickly.
It was built as a collaborative project between Avail, and the Equilibrium Group.
Highlights
- The OpEVM SDK shows how optimistic rollups can be constructed without enshrined bridges, while still having a decentralized sequencer set and permissionless watchtowers.
- OpEVM is built to work atop Avail and to demonstrate that it is possible to run a performant appchain on Avail.
- OpEVM is a community initiative, not intended to compete with existing rollup solutions. We invite the rollup and application developer community to contribute and build using OpEVM.
- Its primary ambition is to push the rollup design space forward.
- It is for developers looking to deploy a new appchain who need flexibility, efficient operation, and code/tool reusability.
- OpEVM is a working prototype of a modular rollup design that enables developers to build sovereign, optimistic, and EVM-compatible rollups on top of Avail.
Features
Shared Sequencer sets
Traditional rollups currently employ a centralized sequencer. This introduces a single point of failure into the rollup’s design and can also reduce the liveness and censorship-resistance guarantees of the rollup.
OpEVM solution: 
OpEVM Stack supports a decentralized sequencer set to order transactions and add them to blocks. This approach amplifies the liveness, decentralization, and censorship-resistant properties of rollups. A PoS-based sequencer-choosing mechanism ensures fair sequencer selection and slashing in case of bad block generation.
Permissionless Watchtowers
Most fraud-proof secured systems often necessitate the whitelisting of entities before they can participate in dispute resolution at least in current implementations.
OpEVM solution: OpEVM stack employs a permissionless system where anyone can submit fraud proofs. The open design of OpEVM promotes inclusivity and transparency, ensuring that the system is accountable to all its users. It also implements slashing in case of incorrect fraud proofs to prevent DoS attack vectors.
Flexibility
Developers need flexibility to iterate as they develop their applications. Smart contract-verified rollups are cumbersome to update, hence making it less flexible for developers.
OpEVM solution: Sovereign chains are more easily updated without relying on smart contracts. Instead of relying on a smart contract on a separate L1, rollup participants resolve any disputes regarding correct execution all on their own.
Efficient operation
Developers need high throughput solutions and no imposition on users to re-execute transactions. Traditional smart contract-based rollups, such as ones enshrined on Ethereum, send transaction data or state transitions to Ethereum, which not only increases costs to the rollup and the end user but also reduces throughput.
OpEVM solution: 
OpEVM provides high throughput operation that sequences transactions and publishes transaction data to ANY data availability layer (even Bitcoin!). This enables the construction to choose optimized DA layers like Avail behind the scenes for efficiency - by benefiting from Avail’s general purpose and scalable DA blockspace - and is also considerably cheaper.
Code/Tool Reusability
Developers need to be able to reuse existing tooling and code written for existing chains. There is a wide variety of tooling and software for EVM-compatible chains. Many developers are familiar with them, or already have existing code they want to migrate or reuse.
OpEVM solution: 
EVM compatibility means that a wealth of software and services just work out of the box, including:
- Popular EVM developer tooling (such as e.g. Hardhat)
- Pre-written contracts written for EVM chains
- Clients (e.g. end user wallets) that can interact with the active sequencer using an EVM-compatible interface.
Take a look at our comprehensive blog where we go more into the technical components of the OpEVM and what teams can expect when utilizing the OpEVM Stack
Status
In summary, the OpEVM SDK suggests that the current way rollups are built is not the only way rollups can be built. By leveraging Avail as a base layer and employing a unique architecture that enables self-resolving rollups, OpEVM proposes a prototype for an efficient, scalable, and secure model for building optimistic Layer-2 solutions.
The OpEVM SDK is currently a feature-complete prototype. However, there is still room for improvement before it should be used for any production-level deployment.
Take a look at our Issues list if you’re interested in tackling them.
Appendix
- OpEVM announcement blog post
- Source code repository
- Using the OpEVM - DEMO
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