What is the Fusaka Upgrade? Ethereum’s largest scaling bet to date

The next big upgrade for the Ethereum network is on the horizon. Called Fusaka – short for “Fulu-Osaka” – the release is scheduled for December 2025 and will combine significant changes to both Ethereum execution and consensus layers.

Fusaka follows several milestones for the Ethereum network following The Merge in 2022. Shanghai/Shapella introduced ETH withdrawals in 2023, Dencun added proto-dankharding and blobs in 2024, and Pectra brought validator flexibility and layer 2 interoperability in 2025.

According to the project roadmap, Fusaka is designed to expand data capacity, strengthen defenses against denial-of-service attacks and introduce new tools for developers and users.

The changes are drastic. Fusaka is not a minor patch, but a redesign of the way Ethereum manages data availability, blob pricing, and transaction security. Its success will be measured by whether the network can scale to meet rising layer-2 demand without breaking or overloading node operators.

PeerDAS: Sampling instead of storing everything

Fusaka’s central feature is PeerDAS, short for ‘data availability sampling’, a new way of handling blob data.

In Ethereum, a blob is a temporary data packet introduced with proto-dankharding as part of the Dencun upgrade. Blobs allow layer-2 rollups to cheaply post large amounts of transaction data to the mainnet, improving scalability without permanently swelling the state of the blockchain.

That provides redundancy, but creates a bottleneck as demand grows. In the current model, each full node on Ethereum must store every ‘blob’ layer 2 data posted to the chain.

PeerDAS changes the equation. Each node will store only a fraction of the blob data (about an eighth) and rely on cryptographic reconstruction to fill in missing pieces. The design is based on random sampling to verify data availability with extremely low probabilities of error, on the order of one in 10²⁰ to 10²⁴.

By distributing storage in this way, Ethereum can theoretically support up to eight times more blob throughput without demanding higher hardware or bandwidth from node operators. Merges, which rely on blobs to publish compressed transaction data, are expected to benefit most directly.

Blob economics and flexibility

Fusaka is also changing the way blob data is priced and managed.

One major change, EIP-7918, introduces a reserve fee for blobs. Under current rules, blob prices could collapse to near zero if execution gas fees dominate. This creates incentives for inefficient use. The reserve fee ensures that blob usage always incurs a base charge, making Layer 2 networks pay for the storage and bandwidth they consume.

Another mechanism, EIP-7892, introduces blob-only parameter forks. This allows Ethereum clients to adjust blob throughput outside of full hard forks. The goal is to give developers the flexibility to respond to unpredictable Layer-2 demand without waiting for the next scheduled upgrade.

Guard against attacks

Scaling also means expanding Ethereum’s attack surface. Fusaka includes a series of changes to mitigate worst-case scenarios and protect the network from denial-of-service attacks:

• EIP-7823: caps the input size for the MODEXP operation at 8192 bits.
• EIP-7825: sets a gas limit per transaction of 2²⁴ units.
• EIP-7883: increases gas costs for large exponents in MODEXP to better match computation efforts.
• EIP-7934: caps execution block size at 10 MB.

Together, these changes reduce the risk that extreme transactions or oversized blocks could overload customers, slow distribution, or create instability.

New tools for users and developers

Fusaka also aims to improve usability.

For users, EIP-7917 introduces support for pre-confirmation. This allows wallets and applications to look ahead at the submitter’s schedule, allowing users to commit that their transaction will appear in an upcoming block. The result is lower latency and less uncertainty about recording.

For developers, Fusaka adds two notable features:

• A CLZ opcode (count leading zeros), useful for cryptographic routines and contract efficiency.
• EIP-7951which provides native secp256r1 (P-256) signature verification. This is a common elliptic curve used in hardware devices and mobile systems, and its addition improves compatibility and account abstraction.

These changes are intended to reduce friction for application developers and pave the way for new wallet designs and security models.

What ETH holders need to know

For regular Ethereum users, Fusaka requires no action. Account balances, tokens and applications will continue to function as before. Ethereum.org emphasizes that users should ignore scams asking them to ‘upgrade’ ETH or transfer money– there is no such requirement.

The responsibility lies with validators and node operators, who must incrementally upgrade their execution and consensus clients. Coordination remains a delicate process: if validators are out of sync, the network risks downtime or temporary chain splits.

After a series of successful testnet activations, the Fusaka upgrade will hit the Ethereum mainnet on December 3, 2025.

The future of Ethereum after Fusaka

Fusaka represents one of the boldest steps in Ethereum’s roadmap since the merger. It’s an effort to deliver more blob capacity, tighter defenses, and new developer tools in one coordinated release.

Testing and DevNet trials are underway, with customer teams focusing on PeerDAS performance, blob pricing models, and compatibility between execution and consensus software. If successful, Fusaka could mark a turning point in Ethereum’s ability to scale for the next wave of layer 2 adoption.