Ethereum Activates Fusaka Upgrade, Unlocking Real Sharding for the First Time

Ethereum has shipped its most ambitious scaling milestone in years, the Fusaka upgrade, the network’s second major update of 2025, is now live on mainnet.

It activated at epoch 411392 on December 3, 2025, at roughly 21:49 UTC, marking a breakthrough moment that researchers have pursued for nearly a decade.

Fusaka introduces PeerDAS, a data availability sampling system that dramatically boosts throughput while lowering costs for rollups. For the first time, Ethereum validators can verify only tiny segments of data instead of full blob payloads. It’s a shift that many core contributors have called the network’s first real step into full sharding.

PeerDAS Arrives: Ethereum’s Long-Awaited Sharding Vision Begins

PeerDAS sits at the center of the Fusaka upgrade. The system lets validators check small samples of data rather than downloading entire blobs. This change increases blob capacity for rollups by roughly 8×, according to the upgrade specification.

The impact is simple: Ethereum can now safely handle far more L2 activity, with lower fees and stronger guarantees. Instead of relying on full-node data downloads or validator voting, PeerDAS uses client-side probabilistic verification. Validators only need to see a fraction of the data to agree on its availability. And this approach remains robust even in the face of 51% attacks.

In a post celebrating the launch, Ethereum co-founder Vitalik Buterin emphasized how meaningful this moment is. “Sharding has been a dream for Ethereum since 2015,” he wrote. Data availability sampling has been discussed since 2017. Now, after years of research and engineering, the system is real, live on the largest smart-contract network in the world.

Why PeerDAS Matters

Ethereum’s core bottleneck has always been data throughput. Rollups depend on blob space to post transaction data, and blob supply determines both scalability and user fees. PeerDAS solves this bottleneck by making blob verification cheaper and more parallelized across the network.

The effect is immediate:

•  Rollups can push far more data per block.
•  Users see lower fees as rollup costs drop.
•  The network becomes more resilient under load.

PeerDAS marks the largest improvement to rollup bandwidth since EIP-4844 launched in 2024.

But experts note that this is also a foundational shift. Ethereum is no longer designed around monolithic validation. It now reliably reaches consensus without requiring any single node to view all the data. This is the core design principle behind modular blockchains, and Ethereum has now taken its biggest step yet toward that future.

Three Ways Fusaka’s Sharding Is Still Incomplete

Despite the massive leap forward, researchers stress that Fusaka delivers the first stage of Ethereum’s sharding roadmap, not the final form.

Vitalik Buterin outlined three gaps that still remain:

1. L1 Still Lacks Full Throughput Benefits

PeerDAS enables L2s to process O(c²) transactions, where c is per-node compute. But Ethereum’s Layer 1 cannot enjoy the same scaling until ZK-EVMs mature. These proving systems are required for the base chain to scale internally rather than relying only on rollups.

2. The Proposer-Builder Bottleneck

Today, block builders must still process all data to build full blocks. This creates a centralization pressure point. A future version of sharding requires distributed block building, where multiple parties collaborate to assemble blocks without any single participant holding all the data.

3. No Sharded Mempool Yet

Ethereum still uses a global mempool. A truly sharded system requires a sharded mempool, allowing different parts of the network to handle transactions independently. This is a key missing piece for full horizontal scalability.

Even with these limitations, Fusaka stands as the most important architectural update to Ethereum since The Merge.

What Fusaka Includes: A Full Breakdown of New EIPs

The upgrade bundles multiple improvements beyond PeerDAS. Each pushes Ethereum toward more performance, better user experience, and smoother execution.

• EIP-7594: PeerDAS

Enables data availability sampling and significantly expands blob throughput, roughly 8× more capacity for rollups.

• EIP-7935: Higher Block Gas Limit

Raises the default block gas limit to 60 million, giving L1 more breathing room for computation-intensive transactions.

• EIP-7951: secp256r1 (R1 Curve) Precompile

Adds native support for the R1 signature curve. This enables faster, cheaper, and more seamless wallet experiences, especially for mobile and Web2-compatible cryptography.

• EIP-7917: Proposer Lookahead

Introduces lookahead windows for block proposers, unlocking pre-confirmations and reducing latency for users.

• EIP-7892: BPO Framework

Creates a structured system for progressively increasing blob targets, allowing the network to scale carefully without risking stability.

• Additional upgrades

Includes ModExp enhancements, the CLZ opcode, networking improvements, and other refinements across the execution and consensus layers.

The combination of these upgrades showcases Ethereum’s continued focus on efficiency, usability, and long-term decentralization.

Network Stability and What Comes Next

Following activation, the Ethereum network shows high validator participation and stable performance. No major incidents have been reported. Client teams continue to monitor PeerDAS behavior, as scaling changes of this magnitude require careful observation in real environments.

The next step arrives soon: BPO1 on December 9, which increases the blob target/max to 10/15. This will expand throughput even further and test the stability boundaries introduced in Fusaka.

Researchers expect the next two years to focus on:

•  Refining PeerDAS
•  Gradually raising blob capacity
•  Scaling L2 ecosystems
•  Advancing ZK-EVM performance
•  Paving the way for L1 scalability through full sharding

Fusaka sets the stage. The roadmap ahead brings Ethereum deeper into its modular era.

A Milestone Years in the Making

Fusaka is more than an upgrade. It is a landmark achievement shaped by thousands of researchers, client developers, security teams, and community contributors. After years of exploration, simulation, and design, Ethereum finally has a functional implementation of data availability sampling on mainnet.

It redefines what the network can do today, and what will be possible tomorrow.

The era of real sharding has begun.

Disclosure: This is not trading or investment advice. Always do your research before buying any cryptocurrency or investing in any services.

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