Ethereum’s Fusaka upgrade: What to expect from the network’s next leap forward

TL;DR: Fusaka is Ethereum’s next major scaling upgrade, introducing PeerDAS to make L2 data posting cheaper and more efficient, enabling dynamic increases to blob capacity, improving core security and networking, and adding UX enhancements like passkey support. It won’t reduce mainnet fees directly, but L2 costs will fall steadily as blob limits rise through 2026 — strengthening Ethereum’s modular settlement strategy.

Ethereum is preparing for its next major protocol upgrade, Fusaka, which will activate on December 3, 2025. This upgrade comes at a time when activity on layer-2 networks is rising rapidly and the current data capacity on Ethereum is being pushed to its limits. Fusaka aims to resolve these bottlenecks through a combination of performance improvements, new scaling tools, and refinements across both the execution and consensus layers.

Here’s what to expect, why Fusaka matters, and how it fits into Ethereum’s long-term roadmap.

How we got here: From the Merge to Pectra

Understanding this progression matters because Fusaka isn’t a standalone fix — it’s the latest step in a roadmap years in the making.

Fusaka is not an isolated overhaul — it’s the next step in a multi-year transformation that has steadily reshaped Ethereum.

The journey accelerated with the Merge in 2022, when Ethereum transitioned from proof-of-work to proof-of-stake. This shift drastically reduced energy consumption and unlocked the flexibility needed for more sophisticated upgrades. Two years later, Dencun introduced “blobs,” a new data format created specifically to help layer-2 rollups post their compressed transactions more cheaply and securely on Ethereum.

In early 2025, Pectra pushed scaling further by increasing blob capacity and stabilising the network for heavier rollup usage. It also laid some of the groundwork for data availability sampling (DAS), the core idea underpinning Fusaka’s marquee feature. Taken together, these upgrades established the architecture that Fusaka now builds upon: a modular ecosystem where layer-2s handle most of the throughput and Ethereum acts as the settlement layer.

Why Fusaka? A network straining under its own success

This is the context in which Fusaka emerges — not a cosmetic improvement, but a response to real pressure on Ethereum’s data layer.

The explosive growth of layer-2 networks like Arbitrum, Optimism, Base, and zkSync has been positive for users but challenging for Ethereum’s data bandwidth. These L2s submit their batched transactions to Ethereum in “blobs,” and as usage surged, data throughput began regularly hitting existing limits. Posting data during busy periods became more expensive, validators were forced to download entire blobs to confirm availability, and node operators struggled with higher network loads.

Ethereum needed a way to scale data availability without compromising security or decentralisation. Fusaka is designed precisely for this problem.

PeerDAS: Fusaka’s most transformative feature

This is the heart of the upgrade — where Ethereum’s data scaling takes a long-awaited leap.

Fusaka’s headline feature is Peer Data Availability Sampling (PeerDAS), a new protocol that changes how nodes confirm that blob data posted by layer-2s is truly available.

Before Fusaka, every node had to download each blob in full to verify that the data existed — a secure but increasingly inefficient approach. After Fusaka, nodes will instead confirm data availability by sampling only small pieces of it. Blob data is split into segments and distributed across the network, with each node responsible for only a small fraction. Cryptographic techniques ensure that the entire blob can be reconstructed if enough segments are available, making missing or incorrect data statistically improbable.

The practical effect is significant. PeerDAS reduces bandwidth and storage requirements for node operators while unlocking the ability to safely scale rollup data throughput. For users on layer-2 networks, this translates into lower posting costs, more predictable fees, and faster overall throughput — without demanding more powerful hardware from validators or full nodes.

Continuous scaling through blob parameter–only forks

PeerDAS allows scaling — BPO forks allow Ethereum to scale continuously.

PeerDAS introduces the capability to scale, but Ethereum also needed a mechanism to adjust posting limits between major hard forks. Fusaka delivers this through blob parameter–only (BPO) forks, which allow the network to raise blob targets quickly and safely without bundling changes into massive coordinated upgrades.

The first two BPOs are already scheduled: one shortly after Fusaka’s activation will increase blob capacity from 6/9 to 10/15 per block, and a second in early 2026 will increase it again to 14/21. This marks the beginning of a more flexible, steady scaling approach in which rollups benefit from expanding data room on a regular cadence rather than waiting months for the next named upgrade.

Improving Ethereum’s core: Security, efficiency, and network hygiene

While scaling is the headline, Ethereum also gets stronger at the base layer.

Although the main focus of Fusaka is scaling L2 data bandwidth, the upgrade introduces several foundational refinements to Ethereum’s base layer.

Cryptographic operations receive new guardrails and updated pricing through improvements to the ModExp precompile, ensuring that large mathematical computations cannot degrade network performance or stall block validation. The introduction of a 16.7 million gas cap for individual transactions further strengthens Ethereum’s resilience, preventing a single oversized operation from monopolising an entire block as gas limits rise in the future.

Networking also gets streamlined. Legacy fields from the pre-Merge era are removed, reducing sync bandwidth and making the protocol cleaner and easier to maintain. Coordinated client work also raises the default block gas limit to around 60 million, expanding L1 execution capacity while maintaining safety through the new transaction-level cap and better resource pricing.

These improvements make Ethereum more efficient, more predictable, and better prepared for future scaling stages.

A better user experience: From passkey support to developer quality-of-life

Not all improvements are visible — but the UX uplift is real.

Fusaka also delivers meaningful user-experience enhancements — subtle in appearance but significant in impact.

One of the most important is native support for the secp256r1 signature scheme, used widely across Apple, Android, and passkey-based authentication systems. This allows wallets to authenticate users via secure hardware that billions of devices already support, making onboarding smoother and reducing reliance on seed phrases.

Developers benefit from new tools as well. The addition of the CLZ (count leading zeros) opcode makes certain bit-level operations cheaper and faster, helping everything from data parsing to compression algorithms to zero-knowledge proofs. A new deterministic proposer lookahead mechanism also improves coordination for validators and enables smoother pre-confirmation systems, reducing UX friction for advanced applications.

Why Fusaka matters: A shift in Ethereum’s scaling strategy

Fusaka is not just an upgrade — it’s the beginning of a more agile Ethereum.

Fusaka marks a subtle but important evolution in Ethereum’s roadmap. Rather than relying solely on giant, infrequent hard forks to deliver major improvements, the network is beginning to adopt a more fluid, modular scaling approach. PeerDAS provides the foundation for high-throughput rollups, and BPO forks allow the network to expand that throughput dynamically. Base-layer refinements ensure that Ethereum stays robust even under increasing load, while UX and developer upgrades help broaden the appeal of building and transacting on Ethereum.

It’s an upgrade that strengthens Ethereum not just technically, but economically. Improved L2 data bandwidth reduces costs for applications, makes fees more stable, and positions Ethereum more competitively relative to other high-throughput ecosystems. It also reinforces Ethereum’s long-term vision of becoming the settlement layer for a global, decentralised financial system.

Will it lower fees?

Not directly on mainnet. L1 gas prices remain governed by demand for block space. But for layer-2 networks, Fusaka is explicitly built to reduce posting costs and stabilise fees. As blob capacity increases through PeerDAS and subsequent BPO forks, rollups gain more breathing room — and users benefit through lower, more predictable fees.

Over time, the experience of “using Ethereum” increasingly becomes “using Ethereum via a layer-2,” and Fusaka plays a central role in enabling that shift.

What users and validators need to do

For everyday users and ETH holders, nothing changes. Your ETH will remain exactly as it is, and there is no such thing as “upgrading” or converting your tokens during the hard fork. Any message suggesting otherwise is a scam.

Validators and node operators, however, must update both their execution and consensus clients to versions that support Fusaka. Running outdated clients will cause nodes to fall out of sync once the upgrade activates, so timely updates are essential.

Nexo will oversee the upgrade

Nexo will oversee the Fusaka rollout across all supported services to ensure everything continues operating smoothly, with no action needed from users. Our engineering and custody teams are coordinating closely with infrastructure partners and monitoring the network throughout activation to guarantee a seamless and uninterrupted experience.

Conclusion: Ethereum is building for the long run

The Fusaka upgrade marks an important moment in Ethereum’s evolution. By expanding rollup data capacity, improving validator security, refining the networking layer, and delivering UX enhancements, Ethereum positions itself for the demands of the next decade.

Behind the protocol changes is a simple outcome: Ethereum becomes faster, cheaper at the edges, easier to use, and better aligned with its modular future — all while maintaining decentralisation.

Fusaka is not the finish line, but it is a meaningful step on the path toward a scalable, global settlement layer.