The Ethereum Fusaka upgrade has been activated on the Holesky testnet. Its core feature, PeerDAS, securely expands blob throughput via data sampling, leading to more stable fees for L2 rollups. This upgrade also improves gas rules, cryptographic tools, and the developer experience, paving the way for a faster and cheaper Ethereum.

Why Fusaka Matters Now

Ethereum is continuously evolving to support more users, transactions, and applications while maintaining security and decentralization. Each upgrade addresses a specific bottleneck. The Dencun upgrade earlier in 4Q24 introduced "blobs," a new data format providing a cheap way for Layer 2 (L2) rollups to store data on Ethereum. This was a major milestone, but demand for blobs quickly hit the cap, causing congestion and driving up fees again.

Today, Ethereum initiated the Fusaka upgrade on the Holesky testnet as the next step forward. The headline feature is Peer Data Availability Sampling (PeerDAS), a method to securely scale blob throughput by allowing nodes to verify data without downloading entire blobs. Beyond PeerDAS, Fusaka also brings improvements to gas rules, cryptographic tools, and the developer experience. For users, this means Ethereum becomes faster, cheaper, and easier to use, especially for the rollups relied upon by millions of users daily. By launching on Holesky before mainnet, Fusaka provides an opportunity for developers, validators, and application teams to prepare for Ethereum's next chapter.

From Dencun to Fusaka

To understand Fusaka's importance, it helps to look back. The Dencun upgrade introduced blobs, allowing rollups to publish batched data to Ethereum at low cost and securely. This breakthrough significantly reduced user fees on networks like Optimism, Arbitrum, and zkSync.

However, demand for blobs grew so rapidly that rollups couldn't always secure blob space, causing fees to spike again. Ethereum needed a way to further scale blob throughput without overwhelming ordinary nodes. This is precisely what Fusaka, launched on Holesky today, delivers.

PeerDAS Explained

The core of Fusaka is PeerDAS (EIP-7594), a new way for Ethereum nodes to check if blob data is truly available.

* The Problem Before Fusaka: Until now, nodes had to download entire blobs even if they only needed to confirm their existence. This was secure but inefficient. Imagine a library where every member had to read every book just to verify it was on the shelf. As more books (blobs) were added to Ethereum blocks, nodes became overwhelmed with unnecessary data, limiting blob throughput and raising fees for rollup users during high demand.

* How PeerDAS Works: PeerDAS uses erasure coding, a mathematical method that splits data into many small pieces. Nodes no longer download entire blobs but instead sample a few pieces from their peers. If enough nodes confirm their random samples, the network can guarantee with extremely high probability that the entire blob is available. It's like a book club where each member randomly checks a few chapters; if all samples agree, the whole group can be confident the entire book is intact without anyone reading it all.

Scaling by Design: The Blob Parameter Only Fork

Ethereum won't massively increase blob capacity all at once. Fusaka introduces the Blob Parameter Only (BPO) fork (EIP-7892), a method to gradually increase blob limits after PeerDAS activation.

On Holesky, the rollout is planned as follows:

* October 7, 2025 – BPO1 increases the blob target from 6 to 10 and the maximum from 9 to 15.

* October 13, 2025 – BPO2 increases the target to 14 and the maximum to 21.

This gradual approach ensures performance can be measured at each step and gives node operators time to adapt their hardware. Instead of a sudden jump, Ethereum scales in controlled, safer increments.

Beyond Blobs: Strengthening Ethereum's Base Layer

Fusaka is about more than just blobs. It also enhances Ethereum's Layer 1 (L1) foundation:

* Gas Rules: The default block gas limit is raised to 60 million (EIP-7935), while a single transaction cannot exceed about 16.7 million gas (EIP-7825). This prevents giant transactions from crowding out others and prepares for future parallel execution.

* Cryptography: Optimizations for modular exponentiation operations (EIP-7883, 7823) improve pricing for complex math. A new precompile (EIP-7951) provides native support for P-256 signatures, widely used for passkeys and device-level security.

* Networking: Removal of legacy Proof-of-Stake fields (EIP-7642) saves bandwidth and simplifies client code.

* Block Encoding: A block size cap is introduced (EIP-7934) to prevent extreme blocks from slowing down propagation.

Together, these changes enhance Ethereum's resilience and efficiency as activity scales.

Building with Fusaka

Ethereum upgrades also focus on usability. Fusaka introduces features that make developers' lives easier and users more secure:

* Passkeys: With native P-256 signature support, wallets can offer passkey login directly on Ethereum.

* Bit-Level Operations: The new CLZ opcode (EIP-7939) reduces costs for compression methods and zero-knowledge (zk) circuits.

* Transparency: Deterministic Proposer Lookahead (EIP-7917) makes the block proposer schedule known in advance, enabling transaction pre-confirmations.

* Predictability: Blob Fee Guarantees (EIP-7918) keep blob fees relatively bounded compared to execution fees, ensuring stable economics.

For developers, these are powerful new tools. For users, they translate to smoother apps, cheaper zk protocols, and more predictable fees.

Testnet Rollout: Holesky Today, Mainnet Coming Soon

Ethereum upgrades always pass through testnets before reaching mainnet. The Fusaka rollout is phased:

* Holesky: Activated on October 1, 2025. BPO1 and BPO2 will follow within two weeks.

* Sepolia: Planned for October 14, 2025.

* Hoodi: Planned for October 28, 2025.

Only after successful upgrades on all three testnets will mainnet activation be scheduled, currently expected in December 2025.

Practical Impact

These technical upgrades translate into real-world benefits:

* Rollup Users: During peak transaction periods, blob slots previously filled quickly, causing fees to spike. With PeerDAS and higher blob capacity, fees will remain more stable.

* Node Operators: Validators upgrading on Holesky today are now compatible with PeerDAS and the new gas rules. Those who do not upgrade will be forked off the chain.

* Application Developers: Wallet teams can support passkey login natively and cheaply.

* ZK Developers: Protocols can use the CLZ opcode to reduce proving costs for zk circuits.

Safety and Governance

Ethereum balances innovation with caution. Alongside Fusaka, a bug bounty program offering rewards up to $2 million has been launched to encourage testing before mainnet.

Fusaka also demonstrates Ethereum's governance model: developers propose Ethereum Improvement Proposals (EIPs), client teams implement them, and node operators decide by upgrading their software. While Fusaka is expected to be non-controversial, the final decision always rests with the community.

Looking Ahead: Ethereum After Fusaka

Ethereum's roadmap unfolds in phases: Dencun, Pectra, Fusaka, and beyond. Each upgrade clears a bottleneck and paves the way for the next. The significance of Fusaka lies in its secure scaling of blob throughput, enabling rollups to handle more transactions while maintaining reasonable node requirements.

* For users, it means cheaper, more reliable L2 experiences.

* For developers, it unlocks tools like passkey authentication and zk efficiency.

* For validators, it proves Ethereum can scale while preserving decentralization.

Conclusion

The Fusaka upgrade launched on Holesky today is more than just another name on the roadmap. It marks the beginning of scaling blobs beyond current limits, powered by PeerDAS and secured through phased forks. It also strengthens Ethereum's foundation from the aspects of gas, cryptography, and networking.

As Fusaka rolls out from Holesky to Sepolia and Hoodi, and then to mainnet, it showcases Ethereum's philosophy: evolve cautiously, inclusively, and with a focus on long-term usability. For the millions of users, developers, and validators worldwide, Fusaka is a concrete step towards a faster, cheaper, and more usable Ethereum.

The Ethereum Fusaka upgrade has been activated on the Holesky testnet. Its core feature, PeerDAS, securely expands blob throughput via data sampling, leading to more stable fees for L2 rollups. This upgrade also improves gas rules, cryptographic tools, and the developer experience, paving the way for a faster and cheaper Ethereum.

Why Fusaka Matters Now

Ethereum is continuously evolving to support more users, transactions, and applications while maintaining security and decentralization. Each upgrade addresses a specific bottleneck. The Dencun upgrade earlier in 4Q24 introduced "blobs," a new data format providing a cheap way for Layer 2 (L2) rollups to store data on Ethereum. This was a major milestone, but demand for blobs quickly hit the cap, causing congestion and driving up fees again.

Today, Ethereum initiated the Fusaka upgrade on the Holesky testnet as the next step forward. The headline feature is Peer Data Availability Sampling (PeerDAS), a method to securely scale blob throughput by allowing nodes to verify data without downloading entire blobs. Beyond PeerDAS, Fusaka also brings improvements to gas rules, cryptographic tools, and the developer experience. For users, this means Ethereum becomes faster, cheaper, and easier to use, especially for the rollups relied upon by millions of users daily. By launching on Holesky before mainnet, Fusaka provides an opportunity for developers, validators, and application teams to prepare for Ethereum's next chapter.

From Dencun to Fusaka

To understand Fusaka's importance, it helps to look back. The Dencun upgrade introduced blobs, allowing rollups to publish batched data to Ethereum at low cost and securely. This breakthrough significantly reduced user fees on networks like Optimism, Arbitrum, and zkSync.

However, demand for blobs grew so rapidly that rollups couldn't always secure blob space, causing fees to spike again. Ethereum needed a way to further scale blob throughput without overwhelming ordinary nodes. This is precisely what Fusaka, launched on Holesky today, delivers.

PeerDAS Explained

The core of Fusaka is PeerDAS (EIP-7594), a new way for Ethereum nodes to check if blob data is truly available.

* The Problem Before Fusaka: Until now, nodes had to download entire blobs even if they only needed to confirm their existence. This was secure but inefficient. Imagine a library where every member had to read every book just to verify it was on the shelf. As more books (blobs) were added to Ethereum blocks, nodes became overwhelmed with unnecessary data, limiting blob throughput and raising fees for rollup users during high demand.

* How PeerDAS Works: PeerDAS uses erasure coding, a mathematical method that splits data into many small pieces. Nodes no longer download entire blobs but instead sample a few pieces from their peers. If enough nodes confirm their random samples, the network can guarantee with extremely high probability that the entire blob is available. It's like a book club where each member randomly checks a few chapters; if all samples agree, the whole group can be confident the entire book is intact without anyone reading it all.

Scaling by Design: The Blob Parameter Only Fork

Ethereum won't massively increase blob capacity all at once. Fusaka introduces the Blob Parameter Only (BPO) fork (EIP-7892), a method to gradually increase blob limits after PeerDAS activation.

On Holesky, the rollout is planned as follows:

* October 7, 2025 – BPO1 increases the blob target from 6 to 10 and the maximum from 9 to 15.

* October 13, 2025 – BPO2 increases the target to 14 and the maximum to 21.

This gradual approach ensures performance can be measured at each step and gives node operators time to adapt their hardware. Instead of a sudden jump, Ethereum scales in controlled, safer increments.

Beyond Blobs: Strengthening Ethereum's Base Layer

Fusaka is about more than just blobs. It also enhances Ethereum's Layer 1 (L1) foundation:

* Gas Rules: The default block gas limit is raised to 60 million (EIP-7935), while a single transaction cannot exceed about 16.7 million gas (EIP-7825). This prevents giant transactions from crowding out others and prepares for future parallel execution.

* Cryptography: Optimizations for modular exponentiation operations (EIP-7883, 7823) improve pricing for complex math. A new precompile (EIP-7951) provides native support for P-256 signatures, widely used for passkeys and device-level security.

* Networking: Removal of legacy Proof-of-Stake fields (EIP-7642) saves bandwidth and simplifies client code.

* Block Encoding: A block size cap is introduced (EIP-7934) to prevent extreme blocks from slowing down propagation.

Together, these changes enhance Ethereum's resilience and efficiency as activity scales.

Building with Fusaka

Ethereum upgrades also focus on usability. Fusaka introduces features that make developers' lives easier and users more secure:

* Passkeys: With native P-256 signature support, wallets can offer passkey login directly on Ethereum.

* Bit-Level Operations: The new CLZ opcode (EIP-7939) reduces costs for compression methods and zero-knowledge (zk) circuits.

* Transparency: Deterministic Proposer Lookahead (EIP-7917) makes the block proposer schedule known in advance, enabling transaction pre-confirmations.

* Predictability: Blob Fee Guarantees (EIP-7918) keep blob fees relatively bounded compared to execution fees, ensuring stable economics.

For developers, these are powerful new tools. For users, they translate to smoother apps, cheaper zk protocols, and more predictable fees.

Testnet Rollout: Holesky Today, Mainnet Coming Soon

Ethereum upgrades always pass through testnets before reaching mainnet. The Fusaka rollout is phased:

* Holesky: Activated on October 1, 2025. BPO1 and BPO2 will follow within two weeks.

* Sepolia: Planned for October 14, 2025.

* Hoodi: Planned for October 28, 2025.

Only after successful upgrades on all three testnets will mainnet activation be scheduled, currently expected in December 2025.

Practical Impact

These technical upgrades translate into real-world benefits:

* Rollup Users: During peak transaction periods, blob slots previously filled quickly, causing fees to spike. With PeerDAS and higher blob capacity, fees will remain more stable.

* Node Operators: Validators upgrading on Holesky today are now compatible with PeerDAS and the new gas rules. Those who do not upgrade will be forked off the chain.

* Application Developers: Wallet teams can support passkey login natively and cheaply.

* ZK Developers: Protocols can use the CLZ opcode to reduce proving costs for zk circuits.

Safety and Governance

Ethereum balances innovation with caution. Alongside Fusaka, a bug bounty program offering rewards up to $2 million has been launched to encourage testing before mainnet.

Fusaka also demonstrates Ethereum's governance model: developers propose Ethereum Improvement Proposals (EIPs), client teams implement them, and node operators decide by upgrading their software. While Fusaka is expected to be non-controversial, the final decision always rests with the community.

Looking Ahead: Ethereum After Fusaka

Ethereum's roadmap unfolds in phases: Dencun, Pectra, Fusaka, and beyond. Each upgrade clears a bottleneck and paves the way for the next. The significance of Fusaka lies in its secure scaling of blob throughput, enabling rollups to handle more transactions while maintaining reasonable node requirements.

* For users, it means cheaper, more reliable L2 experiences.

* For developers, it unlocks tools like passkey authentication and zk efficiency.

* For validators, it proves Ethereum can scale while preserving decentralization.

Conclusion

The Fusaka upgrade launched on Holesky today is more than just another name on the roadmap. It marks the beginning of scaling blobs beyond current limits, powered by PeerDAS and secured through phased forks. It also strengthens Ethereum's foundation from the aspects of gas, cryptography, and networking.

As Fusaka rolls out from Holesky to Sepolia and Hoodi, and then to mainnet, it showcases Ethereum's philosophy: evolve cautiously, inclusively, and with a focus on long-term usability. For the millions of users, developers, and validators worldwide, Fusaka is a concrete step towards a faster, cheaper, and more usable Ethereum.