Ethereum's Largest Testnet, Holesky, Set for Sunset After Fusaka Upgrade

Ethereum is preparing to decommission its largest testnet, Holesky, approximately two weeks after the upcoming Fusaka upgrade is finalized in September 2025. This move marks a significant shift in Ethereum's testing infrastructure, transitioning from a single, large-scale testnet to a more specialized and modular approach.

Key Takeaways

• Holesky, Ethereum's most extensive testnet, will be retired two weeks post-Fusaka upgrade finalization in September 2025.

• Hoodi will fully replace Holesky as the new validator-focused testnet, designed to address previous technical issues.

• Ethereum's testing landscape will now feature three specialized testnets: Sepolia (for dApps), Hoodi (for staking), and Ephemery (for short validator cycles).

The End of an Era for Holesky

Launched in September 2023, Holesky was designed to simulate real-world staking conditions at an unprecedented scale, hosting over 1.6 million validators at its peak. It played a crucial role in testing significant upgrades such as Dencun, which aimed to reduce transaction costs via EIP-4844 (Proto-Danksharding), and Pectra, which focused on optimizing validator performance and introducing partial withdrawal mechanisms.

However, the very scale that made Holesky powerful also led to its challenges. In early 2025, following the Pectra upgrade, the network experienced "inactivity leaks," causing thousands of validators to go offline. This resulted in lengthy exit queues, making it impractical to test the full validator lifecycle and hindering the agility required for Ethereum's rapid development.

Enter Hoodi: The Next-Generation Validator Testnet

To overcome Holesky's limitations, Ethereum introduced Hoodi in March 2025. Built with a "merged-from-genesis" model, Hoodi offers a fresh validator set to avoid legacy exit queue issues and features built-in support for Pectra and upcoming upgrades like Fusaka. Its architecture is designed for more resilient, long-term staking simulations, and major infrastructure providers have already begun migrating their tooling to Hoodi.

Ethereum's Evolving Testnet Strategy

With Holesky's retirement, Ethereum is consolidating its testing efforts into three specialized networks:

• Sepolia: For smart contract and dApp development.

• Hoodi: For validator and staking infrastructure testing.

• Ephemery: For lightweight, short validator lifecycle testing, resetting every 28 days.

This segmentation aims to improve reliability and ensure that each testnet is optimized for specific developer needs.

The Fusaka Fork and Future Outlook

The Fusaka upgrade, scheduled for mid-to-late September 2025, will be the final major event on Holesky. Two weeks after its finalization, all remaining validator nodes on Holesky will be shut down, and the network will no longer receive support from client, testing, or infrastructure teams. Fusaka itself introduces enhancements like improved data availability for rollups, distributed validator load, and lower transaction latency.

The closure of Holesky signifies Ethereum's strategic evolution towards streamlined, modular testnets, enabling faster iteration cycles and cleaner infrastructure. Looking ahead, Ethereum is targeting the Glamsterdam upgrade in 2026, which aims to halve block times, separate block validation from execution, and enhance support for ZK-EVM systems, all geared towards improving user experience and scalability, particularly for the layer-2 ecosystem.

Sources

• Ethereum to Shut Down Holešky, Its Largest Testnet Ever, CryptoNinjas.

• Ethereum to Sunset Its Largest Testnet Holesky, Unchained Podcast.

• Largest Testnet Holesky to Close After Fusaka Upgrade, CoinDesk.