Ethereum developers have announced the upcoming Fusaka upgrade, set to activate on the mainnet on December 3, 2025. This significant hard fork follows a structured testing phase on the Holesky testnet, which will begin on October 1, 2025. The Fusaka upgrade is expected to implement between 11 to 12 Ethereum Improvement Proposals (EIPs) focused on enhancing scalability, node efficiency, and data availability, without introducing new features for users.
Christine Kim highlighted that one notable aspect of the upgrade includes a phased approach to expanding blob capacity, with Blob Parameter Only (BPO) forks scheduled to occur two weeks post-Fusaka activation. Initially, the blob limits will remain at 6/9 (target/max), before rising to 10/15 one week later, and ultimately reaching 14/21 blobs within two weeks. This expansion is critical for accommodating larger transaction volumes moving forward.
The recent Developer Call, ACDC #165, confirmed both the public testnet schedule and the BPO fork timeline. The Fusaka upgrade emphasizes backend protocol enhancements over user-oriented features, aiming to make Ethereum’s operation more efficient and less resource-intensive. For instance, the introduction of PeerDAS through EIP-7594 enables validator nodes to verify only small samples of data rather than entire blobs, easing bandwidth and storage burdens, thereby bolstering Layer 2 rollup scalability.
In conjunction with the upgrade, gas limits have recently increased from 30 million to 45 million, with discussions for future expansions targeting up to 150 million—the intent being to significantly enhance transaction throughput. Furthermore, EIP-9698 proposes a substantial gas limit increase over two years to allow for potentially 2,000 transactions per second. However, the Fusaka upgrade has opted to drop plans for a major redesign of the Ethereum Virtual Machine Object Format to streamline the implementation process.
The introduction of bounded base fees for blob transactions via EIP-7918 aims to stabilize transaction costs for data-heavy applications, while improvements in spam resistance and network security are designed to fortify against scalability challenges.
Following a methodical four-phase approach, the rollout process includes the Holesky upgrade on October 1, followed by Sepolia on October 14 and Hoodi on October 28. Each will participate in the complete BPO fork sequence to validate the blob expansion mechanism. The BPO forks will be activated automatically based on preset epochs.
Node operators have clear deadlines for upgrades, ranging from September 25 for Holesky to November 3 for mainnet preparations. This staggered approach is intended to ensure extensive testing and adequate preparation time for infrastructure providers, while also maintaining backward compatibility to facilitate smooth transitions and minimal disruption.
The timely rollout of PeerDAS may also lower the resource demands on nodes, thereby fostering greater network decentralization by making it easier for smaller operators to participate. The planned enhancements and raised gas limits are essential to enable Ethereum to manage elevated transaction volumes effectively while upholding its security standards.
As pressures mount for Ethereum to improve its base layer amidst criticism of Layer 2 fragmentation, the Fusaka upgrade aims to bolster base layer capacity while supporting the ongoing growth of Layer 2 solutions. Recent concerns regarding validator queues, where over 2 million ETH face delays in exiting, have intensified discussions about network scalability.
In response, Vitalik Buterin stressed the importance of these delays for network security, likening them to committed service requirements. As institutional interest in Ethereum intensifies, with firms like VanEck predicting a potential $1 trillion market cap for Layer 2 networks within six years, the Fusaka upgrade supports Ethereum’s broader ambition for better cross-chain interoperability.
By refining data availability and node efficiency, the upgrade aligns with other initiatives, such as the Open Intents Framework, which aims to tackle the surge in cross-chain crime and unify the fragmented multichain experience while preserving Ethereum’s security and decentralization ethos.
