Ethereum Welcomes Major Testnet Release Ahead of Fusaka Upgrade

Ahead of the planned Fusaka upgrade on Ethereum, the blockchain has welcomed a major testnet. Nimbus, an Ethereum consensus layer client that runs Ethereum’s proof-of-stake network, announced the testnet in an update on X.

Nimbus release prepares testnets for Fusaka transition

According to Nimbus, a new version, CL “v25.9.1” is out now. Users who are running Nimbus on the Ethereum mainnet do not need to immediately upgrade. They could run the upgrade at their convenience.

However, it is a “high-urgency release for the Hoodi, Sepolia, and Holesky testnets.” Holesky testnet is scheduled to end on Sept. 30, 2025, and Hoodi will replace it for validator testing. This time frame has necessitated urgency for developers.

The release aims to address technical fixes like synchronization issues and beacon API enhancements. These tools are critical to ensuring Ethereum network stability during the upcoming Fusaka upgrade.

Notably, the Fusaka upgrade is an improvement on the successfully launched Pectra hardfork, which introduced account abstraction and a higher staking limit. The current testnet would help ensure that the Ethereum blockchain’s roadmap is on track.

Developers on Nimbus are currently enjoined to update to ensure compatibility with the Fusaka hard fork. The Fusaka upgrade will focus on scalability and node resilience; as such, validators and nodes on the testnet require the new CL “v25.9.1” version.

Ethereum founder Vitalik Buterin, commenting on the functionality of Fusaka, explained it would be pivotal to scaling and data availability for the blockchain. It will rely on peer-to-peer Data Availability Sampling (PeerDAS).

The goal is to manage data storage by avoiding downloads so that every node does not need to access block data, as it slows the process. Fusaka will allow nodes to access a few selected blocks and verify, so as to save on storage and bandwidth.

Roadmap aligned with Ethereum’s future goals

It is worth mentioning that the Fusaka hard fork has been scheduled to go live in November, barring any challenges. It will mark a critical milestone for the Ethereum blockchain, as it does not interfere with smart contracts but focuses primarily on the efficiency and resilience of nodes.

Some notable improvements that Fusaka will deliver include the EIP‑7892 blob parameter‑only fork. 

The goal is to create blob tweaks for future forks that key into the Ethereum roadmap. The upgrade is to ensure a stable blockchain that ensures that backend upgrades cannot disrupt decentralized apps.