Fusaka¶

Overview¶

Fusaka (Fulu-Osaka) is Ethereum's second major upgrade activated on December 6, 2025, consisting of the execution layer upgrade Osaka and the consensus layer upgrade Fulu. The upgrade was activated on December 6, 2025 at 21:49 UTC and finalized approximately 15 minutes later, marking Ethereum's second upgrade of 2025 and the first upgrade fully aligned with Ethereum's unified roadmap vision.

The core of Fusaka is PeerDAS (Peer Data Availability Sampling), a key technology in Ethereum's scaling roadmap designed to support larger-scale Rollup expansion by optimizing data availability without increasing validator hardware requirements.

Core Features¶

PeerDAS (EIP-7594)¶

Peer Data Availability Sampling is the core feature of the Fusaka upgrade:

How It Works: - PeerDAS splits blob data into smaller units (cells) - Uses sampling and erasure coding techniques - Validators only need to obtain random data fragments rather than downloading complete blobs - Each node only needs to download ⅛ of the data to verify availability - This can be further reduced to 1/16 or 1/32 in the future

Technical Advantages: - Reduced bandwidth requirements: Decreases bandwidth and storage pressure on each node - Supports home stakers: No need for data center-level hardware - Scaling potential: Paves the way for eventually achieving 8x blob capacity growth - Security guarantee: Solves withholding attacks through random sampling; the larger the network, the lower the probability of a successful attack

Sampling Mechanism: - PeerDAS defines "samples" as "columns," which are cross-sections across all blobs - Compared to "rows" (i.e., complete blobs), column sampling is more efficient - Uses a pseudo-random sampling scheme where the attack success rate decreases sub-linearly as network size grows

Blob Parameter Only Forks (BPO Forks)¶

Fusaka introduces the Blob Parameter Only (BPO) fork mechanism: - Allows increasing the number of blobs per block over time - No need to wait for a full hard fork to adjust blob parameters - Enables a more flexible scaling strategy - Dynamically adjusts data availability capacity based on network conditions

Gas Limit Increase¶

EIP-7935: Coordinated **Gas Limit Increase** - Coordinates execution layer client teams to raise the default gas limit - The current 45M gas limit will be increased - Provides space for more complex smart contract interactions - Supports higher transaction throughput

Roadmap Positioning¶

Unified Protocol Strategy¶

The Ethereum Foundation has outlined a "protocol"-centric strategy around three long-term goals: 1. Scale L1: Increase mainnet throughput 2. Scale blobs: Increase data availability capacity 3. Improve user experience: Lower barriers to usage

Fusaka is the first upgrade fully aligned with this unified vision, deeply advancing the Surge (Scaling), Verge (Verification), and Purge (Cleanup) stages of Ethereum's roadmap.

A New Era of Value Accrual¶

Fidelity Digital Assets states that the Fusaka upgrade marks a new era for Ethereum's value accrual. Through PeerDAS and BPO fork mechanisms, Ethereum can continuously enhance scaling capabilities while maintaining the network's decentralization characteristics.

Technical Impact¶

Reduced Node Costs

PeerDAS significantly lowers the hardware and bandwidth requirements for running validator nodes: - Storage requirements reduced by approximately 87.5% (⅛ of the data) - Bandwidth requirements significantly reduced - Supports running full nodes on ordinary hardware - Increases the degree of network decentralization

Accelerated Layer 2 Settlement

More blob capacity means L2s can submit more transaction data
L2 transaction fees further decrease
Settlement speed improves
Supports more Rollups running simultaneously

Progress Toward Full Danksharding

Fusaka is an important milestone on the path to full Danksharding: - PeerDAS is a key component of Danksharding - Validates the feasibility of data availability sampling - Lays the foundation for larger-scale future scaling - Goal: Eventually support 16MB/second data throughput

Relationship with Pectra¶

Continues Pectra: Fusaka builds on Pectra's increased blob capacity (3->6->9) by further optimizing the data availability mechanism through PeerDAS

Complementary Features: - Pectra focuses on account abstraction and staking improvements - Fusaka focuses on data availability and scaling - Together, they advance Ethereum's scalability and usability

Subsequent Roadmap¶

Glamsterdam (2026)¶

After Fusaka, Ethereum's roadmap continues to "Glamsterdam", planned for release in 2026: - Combining "Glamour" and the Devcon host city "Amsterdam" - Will further advance various stages of the roadmap - Continues to optimize network performance and user experience

Twice-Yearly Upgrade Cadence¶

The rollout of Fusaka establishes Ethereum's new upgrade cadence: - Two major upgrades per year - Faster iteration and improvement - More timely response to ecosystem needs - Maintaining technological leadership

Community and Ecosystem Impact¶

Developer Preparation

Ethereum developers actively prepared for the Fusaka upgrade in November 2025, ensuring client compatibility and smooth transition.

L2 Ecosystem Benefits

Rollup projects (such as Arbitrum, Optimism, zkSync, Starknet, etc.) will directly benefit from the cost reduction and capacity increase brought by PeerDAS.

Enhanced Value Proposition

Through continuous technical upgrades, Ethereum solidifies its position as a scalable, decentralized settlement layer, attracting more users and developers.