Ethereum Foundation Alerts L2s to Software Update Needs on Sepolia Testnet Ahead of Fusaka Upgrade

Executive Summary

The Ethereum Foundation has issued an alert concerning the current non-functionality of certain Layer 2 (L2) deployments on the Sepolia testnet. This issue stems from modifications to the proof format introduced by EIP-7549. The Foundation urges all Blob initiators to update their software to generate Cell Proofs rather than Blob Proofs in anticipation of the forthcoming Fusaka upgrade. This technical adjustment is critical for ensuring the continued compatibility and stability of L2s within the evolving Ethereum ecosystem, though it necessitates immediate development efforts from affected projects.

The Event in Detail

The recent malfunction of some L2 deployments on the Sepolia testnet is directly attributable to EIP-7549, also known as PeerDAS. This Ethereum Improvement Proposal fundamentally alters the format for proofs, transitioning from blob proofs to cell proofs. The primary objective of this change is to enhance data availability sampling, allowing validators to download only specific segments of a blob rather than the entire data unit. While existing signed transactions remain valid, they now require recomputation to align with the new cell proof format. Client software, such as go-ethereum, can perform this conversion via RPC (Remote Procedure Call) on eth_sendTransaction and eth_sendRawTransaction, though this process incurs approximately one second of overhead per transaction. To mitigate this overhead and ensure seamless operation, blob transaction originators, particularly L2s, are advised to proactively update their transaction sending code to directly create cell proofs. Major client libraries provide the necessary functionality, specifically through the ComputeCellsAndKZGProofs() function, to facilitate this transition.

Market Implications

The technical alert from the Ethereum Foundation introduces a degree of uncertainty within the L2 development community. While testnet issues are a part of the development lifecycle, this specific incident highlights the continuous demand for L2 developers to adapt to core protocol changes. In the short term, this will likely result in an increased workload for L2 development teams, potentially leading to delays in deployments if software updates are not promptly implemented. However, in the long term, this mandatory update is crucial for maintaining the health and compatibility of the broader Ethereum ecosystem. It underscores the importance of proactive testing and adherence to evolving standards as Ethereum progresses with significant upgrades like Fusaka. The successful resolution of such issues ensures the reliability and security of L2 solutions as they integrate more deeply with the mainnet.

Expert Commentary

The Ethereum Foundation has emphasized the importance of L2s and other entities closely following the ACD process (All Core Devs) and engaging more directly with the community. This engagement is vital for understanding and contributing to the Ethereum roadmap. Teams are strongly encouraged to deploy and test their contracts and infrastructure on devnets before moving to public testnets. Devnets, which are local blockchain development environments, allow for rapid development, troubleshooting, and end-to-end testing with simulated networks, offering flexibility in configuring various scenarios. The Foundation also recommends leveraging tools like the Kurtosis Ethereum package for creating local networks with the latest specifications. Kurtosis provides a composable build system for multi-container environments, offering greater control and flexibility for developers in configuring their testnets, a method the Ethereum Foundation itself utilizes for testing network upgrades.

Broader Context

This required update is a preparatory step for the significant Fusaka upgrade, targeting mainnet activation by December 3, 2025. Fusaka is designed to substantially scale Ethereum's transaction capacity by increasing the block gas limit from 45 million to 150 million, alongside introducing new data management techniques like PeerDAS and Verkle Trees. The upgrade is slated to roll out in phases, with testnet activations planned for Holesky (October 1, 2025), Sepolia (October 14, 2025), and Hoodi (October 28, 2025) preceding the mainnet launch. The issue on Sepolia, though causing temporary disruption, exemplifies the efficacy of the testnet process in identifying and addressing compatibility challenges well in advance of a mainnet deployment. This continuous cycle of testing and refinement ensures that the broader Web3 ecosystem, including corporate adoption trends and investor sentiment, benefits from a more robust and scalable Ethereum network. The ongoing transition of L2 testnets, such as Celo's migration to Celo Sepolia, further illustrates the industry's alignment with Ethereum's evolving testnet strategy to foster a cleaner and more efficient development environment.