Ethereum’s Fusaka Upgrade: What to Expect on December 3, 2025

Ethereum is preparing for an impending network upgrade known as Fusaka, which will be activated on December 3, 2025.

The hard fork seeks to dramatically improve the blockchain’s handling of data, scalability, and economics — sowing more seeds for its maturing ecosystem of layer-2 solutions and decentralized applications (dApps). 

Here’s an overview of what is ahead, why it is important, and what users, developers, and validators need to watch.

What is Fusaka?

Fusaka is Ethereum’s upcoming hard fork, one of the network’s continuous roadmap to scale, enhance security, and lower costs. It includes a series of Ethereum Improvement Proposals (EIPs) aimed at data availability, enhancing layer-2 integrations, and increasing transaction throughput.

Among them, PeerDAS (Peer Data Availability Sampling) stands out as a critical innovation, and changes in “blob”

The primary technical changes and improvements Fusaka offers are as follows:

PeerDAS (Peer Data Availability Sampling): A system that aims to enable nodes to check data availability without needing to download the entire data themselves. This eliminates bandwidth and storage needs while retaining network security and integrity.

Expanded Blob Capacity: Blobs are used for off-chain storage of large datasets, which layer-2 rollups rely upon. Fusaka will more than double the current blob capacity via Blob-Parameter-Only (BPO) hard forks. The plan is to gradually increase blob target/maximum blob counts. 

Testnets Ahead of Mainnet: To ensure stability, Ethereum will (or already has) run the upgrade through several public testnets, including Holesky (Oct 1), Sepolia (Oct 14), and Hoodi (Oct 28). These help catch bugs, allow clients to adapt, and give developers a chance to test layer-2 interactions. 

Security Audits & Bug Bounty Program: In the run-up to launch, there is a code audit competition with a potential of up to US$2 million rewards to incentivize the community to find and submit vulnerabilities.

The upgrade aims to expand data capacity up to 10x through PeerDAS, boosting Layer 2 solutions like rollups.

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