Overview

The ZKsync OS Developer Preview testnet is a new environment that runs on the latest architecture introduced in the Atlas upgrade. It includes all major components released in that upgrade — ZKsync OS, the new Sequencer, and the Airbender prover — giving developers early access to the full next-generation ZK Stack.

This testnet allows builders to deploy contracts, profile system performance, and explore how the ZK Stack has evolved across execution, sequencing, and proving.

ZKsync OS is the new operating system of the ZK Stack. It defines the system-level state transition function of a chain and supports multiple Execution Environments (EEs).

Unlike earlier implementations, ZKsync OS unifies execution and proving logic in one codebase and compiles it to two targets — x86 for the sequencer runtime and RISC-V for the Airbender proving system.

The Developer Preview testnet runs ZKsync OS alongside the new Sequencer and Airbender prover, providing a complete environment for testing the latest stack.

Architecture

The core protocol is organized into two primary layers:

Execution layer: defines transaction logic, memory handling, and IO. It computes new state from the previous block state and inputs.
Proving layer: generates ZK proofs that attest to the correctness of that state transition.

ZKsync OS is implemented in Rust and compiled to two targets:

x86: used by the Sequencer to execute transactions
RISC-V: used by the Airbender prover to generate ZK proofs of correctness

This “one program, two targets” model ensures what you execute is what you prove, eliminating discrepancies between runtime and proof generation and reducing the audit surface. Execution and proving operate as decoupled services (sequencer vs. prover) while sharing the exact same program and semantics.

Components

ZKsync OS

The core of the system. ZKsync OS provides a modular execution framework that supports multiple execution environments and defines the rules for state transitions.

Bootloader: initializes the system and coordinates transaction execution.
Execution Environments: interpreters that run user contracts and system logic.
System Layer: handles low-level IO (storage, events, L1 messages) and manages memory.

The Developer Preview currently supports a fully EVM-equivalent environment, allowing developers to use existing EVM tools (e.g. Foundry, Hardhat, solc) and deploy contracts without modification. Future versions may include EraVM, WASM and native RISC-V environments.

Learn more about ZKsync OS in the protocol documentation.

Sequencer

The new Sequencer, introduced as part of the Atlas upgrade, is designed for:

High throughput — sustained >15K TPS in ERC-20 transfer benchmarks
Low latency — sub-second inclusion, typically 250–500 ms
Modularity — clear separation of execution, API, and proving layers

It offloads batching and L1 coordination to asynchronous services, simplifying the execution pipeline and improving resilience. For developers, this means faster transaction processing and easier scaling for custom ZK Stack chains.

Airbender Prover

Airbender is the proving system used in the Developer Preview testnet. It is a general-purpose, open-source RISC-V zkVM integrated directly with ZKsync OS.

Key properties:

Efficient hardware utilization — can run on a single GPU.
Low cost — proving an ERC-20 transfer costs roughly $0.0001.
Fast proofs — Airbender can be scaled horizontally to generate ~1 second block proofs and minutes-to-Ethereum finality.

Because both execution and proving compile from the same Rust source, Airbender proves the exact code path executed by ZKsync OS. This reduces audit complexity and guarantees consistency between runtime and proofs.

Learn more about Airbender in the protocol documentation.

Developer Preview Testnet

The Developer Preview testnet includes:

ZKsync OS — modular execution layer with full EVM equivalence.
New Sequencer — redesigned high-performance execution engine.
Airbender — integrated real-time RISC-V prover.

Developers can use this testnet to:

Deploy and test contracts using familiar EVM tooling
Benchmark transaction throughput and latency
Integration test for infrastructure tools
Evaluate how the new architecture supports specific workloads

Paymasters

Paymasters are specialized accounts designed to subsidize transaction fees for users, enhancing usability and flexibility within protocols. They also facilitate the payment of fees using ERC20 tokens, instead of the default ETH.

Network Details

Connect to ZKsync OS Developer Preview testnet