From Dencun to Fusaka: Ethereum's next leap

Compilation: Vernacular Blockchain

Introduction: Why %20Fusaka%20 is so important now

Ethereum continues to evolve to support more users, more transactions, and more applications, while maintaining security and decentralization. Each upgrade targets a bottleneck in the system. Earlier in 2024, the Dencun upgrade introduced "blob" (, a new data format ), providing a new way for Layer 2 (L2) rollups to store data cheaply on Ethereum. This is a significant milestone, but the demand for blobs quickly reached its limit, leading to congestion and driving up fees again.

Today, Ethereum launched the Fusaka upgrade on the %20Holesky%20 testnet, as the next step forward.

Fusaka's headline feature is Peer Data Availability Sampling(PeerDAS), which is a method for securely scaling blob throughput, allowing nodes to verify data without downloading the entire blob. In addition to PeerDAS, Fusaka also improves gas rules, cryptographic tools, and developer experience. For users, this means Ethereum becomes faster, cheaper, and easier to use, especially for rollups that millions of users rely on daily.

By launching on %20Holesky%20 before the mainnet, Fusaka provides developers, validators, and application teams the opportunity to prepare for the next chapter of Ethereum.

from Dencun to Fusaka

To understand the importance of %20Fusaka%, it helps to look back. Earlier in 2024, Ethereum released the %20Dencun%20 upgrade, introducing %20blob%20 as a new data format. Blob%20 allows rollups to publish packed data to Ethereum in a low-cost and secure manner. This breakthrough significantly reduced user fees for networks such as %20Optimism%, %20Arbitrum%20, and %20zkSync%20.

But the demand for blobs is growing so rapidly that rollups cannot always obtain blob space, and fees have skyrocketed again. Ethereum needs a way to further scale blob throughput without overwhelming regular nodes. This is precisely what Fusaka, launched today on Holesky, provides.

PeerDAS%20Detailed Explanation

The core of Fusaka is PeerDAS(Peer Data Availability Sampling, EIP-7594), which is a new way for Ethereum nodes to check the actual availability of blob data.

The issue before Fusaka%20

Until today, nodes must download the entire %20blob, even if they only need to confirm its existence. This is safe, but inefficient.

Imagine a library where each member must read every book to verify that a book is on the shelf. As the number of books increases, this effort becomes unsustainable. Similarly, as more %20blobs are added to the Ethereum Block, nodes become overwhelmed under unnecessary data pressure. This limits the %20blob%20throughput and drives up the fees for %20rollup%20users during periods of high demand.

The working principle of PeerDAS

PeerDAS uses erasure coding (, a mathematical method that splits data into many small pieces ). Imagine tearing a massive book into hundreds of chapters— even random small subsets can prove the existence of the entire book.

Nodes no longer download the entire %20blob, but instead sample several blocks from their peer nodes. If enough nodes confirm their random samples, the network can guarantee with a very high probability that the entire %20blob%20 is available.

It's like a book club where each member randomly checks two or three chapters. If all the samples are consistent, the whole group can be confident that the entire book is intact without anyone needing to read it in full.

Extension in design: fork with only blob parameter

Ethereum will not significantly increase blob capacity all at once. Fusaka introduced the Blob Parameter Only(BPO) fork(EIP-7892), which is a method for gradually increasing blob limits after PeerDAS activation.

The rollout plan on Holesky is as follows:

October 1, 2025 – Fusaka activated at 08:48 UTC.

October 7, 2025 – BPO1 has increased the blob target from 6 to 10, and the maximum value from 9 to 15.

October 13, 2025 – BPO2 has raised the target to 14, with the maximum increased to 21.

This gradual approach ensures that the performance of each step can be measured, giving node operators time to adapt to the hardware. Unlike sudden leaps, Ethereum scales in a controlled and safer incremental manner.

Beyond Blob: Strengthening the Ethereum Base Layer

Fusaka is not just about blob. It also improves the Ethereum layer (L1) foundation:

Gas Rules: The default block gas limit has been raised to 60 million(EIP-7935), while a single transaction cannot exceed approximately 16.7 million gas(EIP-7825). This prevents massive transactions from crowding out other transactions and prepares for future parallel execution.

Cryptography: Optimization of modular exponentiation operations ( EIP-7883, 7823) improved the pricing of complex mathematical operations. The new precompiled ( EIP-7951) provides native support for P-256 signatures, which are widely used for passkeys and device-level security.

Network: Remove the legacy proof-of-stake field (EIP-7642) to save bandwidth and simplify client code.

Block Encoding: Introduced the block size limit (EIP-7934) to prevent extreme blocks from slowing down propagation.

These changes collectively enhance Ethereum's resilience and efficiency during activity scaling.

build with Fusaka

The Ethereum upgrade also focuses on usability. Fusaka introduces features that make life easier for developers and safer for users:

Access Key: With P-256 signature natively supported, the wallet can directly provide access key login on Ethereum ( for iPhone, Android devices, and browsers ).

Bitwise Operations: The new CLZ opcode (EIP-7939) reduces the cost of compression methods and zero-knowledge (zk) circuits.

Transparency: The deterministic proposer foresight ( EIP-7917) makes the block proposer schedule predictable, thereby enabling transaction pre-confirmation.

Predictability: Blob fee guarantee ( EIP-7918) keeps blob fees within relative bounds to execution fees, ensuring stable economics. For developers, these are powerful new tools. For users, they translate into smoother applications, cheaper zk protocols, and more predictable fees.

Testnet rollout: Holesky today, mainnet is coming soon.

Ethereum upgrades always go through the testnet first before reaching the mainnet. The rollout of Fusaka is phased:

Holesky: Launching on October 1, 2025. BPO1 and BPO2 will follow up in two weeks. Holesky will also retire thereafter, marking both a launch and a farewell.

Sepolia: Scheduled for October 14, 2025.

Hoodi: Scheduled for October 28, 2025.

The mainnet activation will only be scheduled after all three testnets have successfully upgraded, which is currently expected to be in December 2025.

Actual changes

These technological upgrades will extend to the benefits of the real world:

Rollup Users: During peak transaction periods, blob slots used to fill up quickly, leading to increased fees. With PeerDAS and higher blob capacity, fees will remain more stable.

Node Operators: The validators that were upgraded on Holesky today are now compatible with PeerDAS and the new gas rules. Those who have not upgraded will be forked off the chain.

Application Developer: The wallet team can support access key login cheaply and natively.

zk Developers: The protocol can use the CLZ opcode to reduce the proof cost of zk circuits.

Security and Governance

Ethereum strikes a balance between innovation and caution. In addition to Fusaka, a bug bounty program has been launched, offering rewards of up to $2 million to encourage testing before the mainnet.

Fusaka also demonstrated the governance model of Ethereum: developers propose Ethereum Improvement Proposal (EIP), client teams implement them, and node operators decide through software upgrades. Although Fusaka is expected to be non-controversial, the final decision is always in the hands of the community.

Outlook: Ethereum after Fusaka

Ethereum's roadmap unfolds in phases: Dencun, Pectra, Fusaka, and further into the future. Each upgrade clears a bottleneck and paves the way for the next step. The importance of Fusaka lies in its ability to securely scale blob throughput, allowing rollups to handle more transactions while maintaining reasonable node requirements.

For users, this means a cheaper and more reliable L2 experience.

For developers, it unlocks tools such as access key authentication and zk efficiency.

For validators, it proves that Ethereum can scale while maintaining decentralization.

Conclusion

The Fusaka upgrade launched today on Holesky is not just another name on the roadmap. It marks the beginning of blob expansion beyond current limits, powered by PeerDAS and secured through phased forks. It also strengthens Ethereum's foundation in terms of gas, cryptography, and networking.

As Fusaka rolls out from Holesky to Sepolia and Hoodi, and then to the mainnet, it demonstrates the philosophy of Ethereum: cautious evolution, inclusive evolution, and a focus on long-term usability. For millions of users, developers, and validators around the world, Fusaka is a concrete step towards a faster, cheaper, and more practical Ethereum.

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