The ZK Stack: A Network Of Composable L2s and L3s

Ethereum Layer 2 zkSync recently announced the ZK Stack: an open-source code base allowing the straightforward and permissionless creation of Zero Knowledge proof-based L2s and L3s. Rollups built on the stack are dubbed Hyperchains, and developers maintain full customizability over their creation.

A notable innovation included in the stack is Hyperbridges, a cross-rollup communication protocol that enables trust-minimized interoperability between Hyperchains thanks to the use of shared mainnet bridge and prover contracts. Anyone can build their own execution environment connected to the greater unified liquidity and user layer that is the zkSync ecosystem. Though today the idea mostly exists in theory, horizontal scaling through ZK rollups with built-in communication provides an extremely promising solution for scaling Ethereum.

Hyperchains: Sovereign Execution Environments

At the heart of the ZK Stack are Hyperchains: layer 2 (or above) rollup execution environments. The ethos behind the ZK Stack is reminiscent of the Cosmos SDK or OP Stack— it freely avails its codebase, allowing developers to innovate without limitations. There's no obligation to settle a Hyperchain on any specific network, and the codebase can be altered or changed in any way a developer pleases.

Each Hyperchain is fully customizable due to the ZK Stack's modularity. Developers can choose their sequencer, data availability layer, and whether to use the shared prover or to settle proofs directly to Layer 1 (among other things) — though the latter option comes at a higher cost. With ZK rollups, the cost per transaction decreases as the number of transactions being verified by a single proof increases.

One particularly interesting aspect of Hyperchains is that they can be Layer 3s or higher up the stack. A ZK L2 takes a plethora of transactions, creates a zero-knowledge proof offchain, and posts the proof to an L1 prover contract. An L3 does the same process but posts its proof to a prover contract that has been deployed to an L2. This type of architecture has been dubbed fractal scaling and is included in the existing roadmap for most of the ZK projects today, such as Starknet.