Ethereum's Phased Fusaka Upgrade Powers Secure, Efficient Scaling

Ethereum’s next major upgrade, codenamed Fusaka, is set to activate on mainnet on December 3, 2025, following a systematic rollout across three public testnets beginning in Octobertitle1^[1]. The upgrade aims to enhance scalability and efficiency by expanding data capacity through a series of Blob Parameter Only (BPO) forks, which will incrementally increase blob limits from 6/9 to 14/21 without requiring client-side software updatestitle2^[2]. This phased approach is designed to safely scale Ethereum’s infrastructure while maintaining network stability.

The testnet deployment schedule includes Holesky on October 1, Sepolia on October 14, and Hoodi on October 28title3^[3]. Developers emphasized that the final activation date and epoch numbers for mainnet will be confirmed based on testnet performance. Fusaka will introduce 11–12 Ethereum Improvement Proposals (EIPs), focusing on backend optimizations such as PeerDAS (Peer Data Availability Sampling), which enables validators to verify data by sampling small portions of blobs rather than downloading entire filestitle4^[4]. This reduces bandwidth and storage requirements, enhancing node efficiency and supporting Layer 2 rollup scalability.

A key feature of Fusaka is the phased expansion of blob capacity. The first BPO fork, scheduled for December 17, 2025, will raise blob limits to 10/15 target/max, followed by a second BPO fork on January 7, 2026, pushing limits to 14/21title5^[5]. These changes are expected to more than double Ethereum’s current blob throughput, building on the March 2024 Dencun upgrade. Analysts noted that average blob counts per block have already risen from 0.9 in March 2023 to 5.1 as of September 2025, underscoring growing demand for efficient data storagetitle6^[6].

The Ethereum Foundation has launched a $2 million bug bounty program to audit Fusaka’s codebase over four weeks, reflecting a prioritization of security amid ambitious scaling goalstitle7^[7]. Gas limit increases, including proposals to raise the block gas limit from 30 million to 150 million, are also part of the roadmap, though developers are cautious about potential trade-offs such as slower block propagationtitle8^[8]. Fusaka’s focus on infrastructure improvements—rather than user-facing features—aligns with Ethereum’s ongoing cadence of upgrades, following May 2025’s Pectra upgrade, which introduced account abstraction and validator staking changestitle9^[9].

The timing of Fusaka coincides with heightened scrutiny of Ethereum’s validator ecosystem. Over 2.6 million ETH (approximately $12 billion) recently entered the exit queue, creating wait times exceeding 40 daystitle10^[10]. While co-founder Vitalik Buterin defended these delays as essential for security, critics argue the backlog risks centralization. Fusaka’s optimizations, including reduced node resource demands and bounded fees for blob transactions via EIP-7918, aim to address such challenges while supporting institutional adoption of Layer 2 networkstitle11^[11].