Modular blockchain architecture has led to a cambrian explosion of scaling solutions and despite the first-mover advantage of optimistic rollups, zero-knowledge (ZK) rollups are lining up to take their seat upon the throne. zkEVM rollups, often referred to as the “holy grail of scaling” as they offer the exact same developer experience as Ethereum, are live on mainnet today. This isn’t some hypothetical future; we can now process large amounts of transactions at low cost on Layer 2 and have the resulting state transition finalized on a decentralized Layer 1 within minutes. Existing solidity developers do not need to learn new programming languages, discover new tools, or even re-write and audit their existing dapps to leverage this new technology. Deploying your dapp to a fully EVM-equivalent zkEVM rollup is as simple as copy paste.

But this scaling technology comes at a price. All rollups, including ZK-rollups and zkEVMs, have a single operator. Upgrade keys for smart contracts are not yet sufficiently decentralized and in most cases the core team has the ability to upgrade the rollup following a waiting period. These “training wheels” are a necessary precaution to protect users’ assets given the relative immaturity of the technology.

To bridge the gap from where we are today to where we need to be in the future, it is therefore mandatory for all Rollup teams to outline their plans for progressive decentralization and trust minimization. At Linea, prior to launching our Mainnet Alpha to the public on July 18th, we presented a 5-phase plan for how we intend to remove our training wheels and deliver a mature rollup solution fully secured by Ethereum. Linea is a developer-friendly Type-2 zkEVM bootstrapped by the leading web3 infrastructure company Consensys.

ZK-rollups inherently offer better security guarantees than optimistic rollups as they rely on cryptography, not cryptoeconomics, to protect the database. Smart contracts on Ethereum verify a validity proof published by the rollup to confirm the integrity of the proposed state transition. For a zkEVM, this requires all of the existing EVM opcodes and precompiles to be proven on the Layer 2. In just a few months, as part of its initial Phase, Linea will offer 100% coverage of all possible execution such that any user or dapp need only trust the proof verification on Ethereum to be convinced that no malicious behavior has taken place. The software and zero knowledge circuits will be open source for anyone to independently verify. The licensing will allow users to view, modify, and fork the code, ensuring that the Linea community can act if the core team is ever to steer away from its intended mission.

Another key step along the path to trust minimization is to enable users to withdraw their assets from a rollup via Layer 1. In the event that a rollup operator chooses to censor a user’s transaction on Layer 2 or simply becomes unavailable, a mechanism should exist that guarantees an exit from the system without permission. This is one of the reasons rollups are the de facto scaling solution for Ethereum as they solve this fundamental data availability problem. Linea plans to enable censorship resistant withdrawals in Phase 2 of its roadmap.

Phase 3 marks Linea’s decentralization of key operational components within its architecture and democratizing its governance system. Decentralizing operators, such as provers and sequencers, strengthens trust among network participants by reducing reliance on centralized entities. There are many technical and operational challenges to this problem as we need to consider consensus, MEV, performance, and UX. No rollup solution has yet to decentralize their operators and we will likely see divergence amongst the systems as the values and principles of each ecosystem are translated into the core architecture.

In the final phase, Phase 4, Linea will focus on realizing the concept of a multi-prover rollup, featuring multiple diverse implementations of a zkEVM prover. Even in the face of potential bugs or availability issues, the use of multiple heterogeneous provers will ensure uninterrupted operation and the reassurance that a single point of failure will not lead to a major fault in the system. This prover diversity is even more important as the EVM specification driven by the Ethereum community continues to evolve and the ZK circuits need to be updated and audited accordingly.

The multi-prover is the fastest path to fully removing training wheels and will likely be the tipping point for reassuring a wave of liquidity and risk-averse businesses to enter the public blockchain paradigm. Many existing zkEVM solutions have taken shortcuts which make a multi-prover more technically challenging to implement, but Linea has been designed from the very beginning to be as close to the EVM specification as feasible.

There is no question that ZK-rollups and zkEVMs are here. Linea is a new zkEVM live on mainnet that is transparent about its current state of maturity and has a clear path to decentralization and trust minimization. We can already see the scalability benefits but there is still work to do to remove training wheels. We believe that by focusing on the end goal from the very beginning, we are in a unique position to be the first zkEVM rollup to realize the full vision of scaling Ethereum.