TL;DR

Ethereum Testnet urgency: Nimbus released CL “v25.9.1” as a high-priority update for Hoodi, Sepolia, and Holesky testnets.
Fusaka focus: Upgrade builds on Pectra, targeting scalability, node resilience, and validator compatibility.
PeerDAS innovation: Vitalik Buterin highlighted data sampling to cut storage needs while boosting efficiency.

Ethereum has taken a significant step toward its next major milestone with the release of a new testnet designed to prepare for the upcoming Fusaka upgrade. The Nimbus consensus layer client announced the deployment of version CL “v25.9.1,” which will play a central role in ensuring the network’s readiness. While the release is optional for mainnet users, it is considered urgent for developers working on Hoodi, Sepolia, and Holesky testnets as Ethereum accelerates toward its December upgrade window.

The Nimbus CL `v25.9.1` is out now

This is a `low-urgency` release for mainnet and `high-urgency` release for the Hoodi, Sepolia, and Holesky testnets, due to impending Fusaka forks on each https://t.co/gpHpJ3fVNn

— Nimbus (@ethnimbus) September 26, 2025

Nimbus Release Targets Testnet Stability

Nimbus confirmed that the CL “v25.9.1” update addresses synchronization issues and enhances the beacon API, both critical for maintaining stability during the Fusaka transition. Although mainnet validators can adopt the update at their convenience, developers on testnets face a tighter timeline. Holesky is scheduled to shut down on September 30, 2025, with Hoodi stepping in as its replacement for validator testing. This urgency underscores the importance of the release in keeping Ethereum’s roadmap on track.

Fusaka Builds on Pectra’s Foundation

The Fusaka upgrade follows the successful Pectra hard fork, which introduced account abstraction and raised staking limits. Fusaka aims to expand on these improvements by focusing on scalability and node resilience. Validators and nodes on testnets are required to adopt the new Nimbus version to ensure compatibility with the hard fork. By refining the network’s technical underpinnings, Fusaka is expected to strengthen Ethereum’s infrastructure without disrupting existing smart contracts.

Vitalik Buterin Highlights PeerDAS Innovation

Ethereum founder Vitalik Buterin emphasized that Fusaka will be pivotal for scaling and data availability. The upgrade will introduce peer-to-peer Data Availability Sampling (PeerDAS), a method that reduces the need for nodes to download entire blocks. Instead, nodes will verify selected portions, saving both storage and bandwidth. This innovation is designed to improve efficiency while maintaining security, ensuring that Ethereum can handle greater demand without compromising decentralization.

Roadmap Aligned With Future Goals

Scheduled for a November launch, the Fusaka hard fork represents a critical milestone in Ethereum’s long-term strategy. Among its notable features is EIP-17892, a blob parameter-only fork that lays the groundwork for future enhancements. By focusing on backend improvements rather than altering smart contracts, Fusaka ensures that decentralized applications remain unaffected. The upgrade reflects Ethereum’s commitment to building a resilient, scalable blockchain capable of supporting its expanding ecosystem.

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Filed under: News - @ September 26, 2025 1:27 pm