The Fusion Upgrade for Ethereum: What You Need to Know Before December 2025

Quick Overview

Ethereum is facing a significant network upgrade called Fusaka, with its mainnet launch scheduled for December 3, 2025. The upgrade will triple the block gas limit from 45 million to 150 million gas, while introducing two revolutionary technologies – Peer Data Availability Sampling (PeerDAS) and Verkle Trees – to optimize data compression and verification.

The Technical News Behind Fusaka

The gas limit is tripled - what does it mean?

The most important change is the increase of the block gas limit from 45 million to 150 million. This allows the Ethereum network to process significantly more transactions, smart contracts, and other operations for each new block added to the blockchain.

This expansion is particularly important for blobs – the data format that Layer 2 solutions rely on to publish transaction information on Ethereum. With higher capacity, these Layer 2 platforms can send more data more efficiently, resulting in faster and cheaper transactions for end users.

PeerDAS revolutionizes data verification

Instead of validators having to download and store complete data shards, Peer Data Availability Sampling (PeerDAS) works through a random sampling system. Validators can now fetch small data cubes from various network nodes and verify that the information is available and correct without having to archive everything themselves.

This innovation significantly reduces bandwidth requirements and allows more operators to participate in the network's security.

Verkle tree for more efficient storage

Verkle trees replace the current data structures with a more compact model to prove the state of the blockchain. The data proof is compressed into smaller units that require less storage space and enable faster verification – a crucial requirement as the blockchain grows.

Why this upgrade is critical for Ethereum

The Ethereum network has grown explosively. Millions of users interact daily with DeFi protocols, NFT platforms, decentralized applications, and Layer 2 solutions. However, this growth has created bottlenecks: slower confirmations and higher transaction fees during peak times.

Fusaka addresses these challenges by:

• Increase block capacity so that more transactions and complex operations can be included per block
• Optimize data blobs for Layer 2 platforms that rely on these to publish their state
• Reduce the storage burden on node operators through PeerDAS and Verkle trees
• Maintain decentralization by ensuring that the network remains accessible to smaller operators

Timeline for Launch and Testing

Fusaka will be rolled out in phases before the mainnet activation:

Each testnet phase gives developers the opportunity to validate performance, security status, and address any issues before the public launch. The exact dates may be adjusted based on the results from these tests.

Who is affected by Fusaka?

User: You can expect faster transaction confirmations during peak times, as the network can handle larger amounts of activity concurrently. Gas fees will become more stable, although they will still fluctuate depending on demand.

Developer: Layer 2 projects will benefit from greater blob capacity and PeerDAS improvements. Rollups and other scaling solutions can transfer more data to Ethereum more efficiently, increasing reliability.

Validators and node operators: Thanks to PeerDAS sampling, validators do not need to download all blob data, which significantly reduces bandwidth usage. However, configuration updates are required to support the new changes.

Security First: Bug Bounty Program

The Ethereum Foundation takes security very seriously. A comprehensive four-week long Bug Bounty program will be conducted prior to the launch of Fusaka, with rewards of up to 2,000,000 USD for identifying critical security issues.

This encourages security researchers and developers in the community to thoroughly review the code and report potential vulnerabilities before the upgrade is activated on the mainnet.

Conclusions

Fusaka represents a crucial development step for Ethereum. By tripling the gas limit and implementing PeerDAS and Verkle trees, the upgrade addresses several long-term scalability challenges. The system can support more users and transactions without compromising the decentralization or security that are core values in Ethereum's design.

With the test phases already in motion and the mainnet launch scheduled for December 2025, the network is heading towards a more efficient and accessible future.