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Fusaka (Fulu-Osaka) went live on Ethereum mainnet on December 3, 2025. It’s a major upgrade designed to help Ethereum’s rollup ecosystem grow without becoming slower, more expensive, or harder to participate in.
In this post, we’ll cover the most important changes Fusaka introduces, why they matter for Layer 2s, and what this upgrade means specifically for Zircuit.
Fusaka is an Ethereum upgrade focused on how rollups publish and verify transaction data. At a high level, Fusaka improves three things:
Together, these changes make it possible for rollups to grow significantly while keeping Ethereum decentralized and accessible.
The most important part of Fusaka is PeerDAS.
Before Fusaka, Ethereum validators checked rollup data by downloading all of it. As rollups grew, this became slow, expensive, and hard to scale.
PeerDAS introduces a smarter approach. Instead of downloading everything, validators only check small samples (about 12.5%) of rollup data. If enough pieces are available, the network can be confident the full data exists.
This change has a large impact:
With PeerDAS in place, Fusaka also expands how much rollup data Ethereum can handle.
Blob space increases by roughly 3.5×, giving rollups far more room to post transaction data. With more space available:
At the ecosystem level, this increase in data capacity pushes Ethereum’s rollup throughput from roughly 12,000 transactions per second (after Pectra) toward 100,000+ transactions per second.
Fusaka also increased Ethereum’s block gas limit from 36M to 60M. In simple terms, this means Ethereum can fit more activity into each block.
This improves baseline network capacity and gives complex applications more room to run smoothly. Additional safety limits ensure this extra capacity doesn’t overload the network.
Another important change in Fusaka is how rollup data fees behave during busy periods.
Instead of fees spiking suddenly when demand increases, Fusaka smooths things out by saving excess fees when demand is low and releasing them when demand is high. This leads to:
For Zircuit and its users, Fusaka directly improves both cost and performance:
Zircuit has already rolled out updates to fully support Fusaka, including protocol compatibility changes and optimizations that reduce proving costs. Zircuit has also strengthened its security tooling, which protected over $3M in user funds during Q3 and Q4, and added additional safeguards against denial-of-service attacks.
Fusaka lifts one of the biggest long-standing limits on Ethereum’s rollup ecosystem. By making rollup data easier to handle and reducing the work required from validators, Ethereum can now scale much further without giving up on decentralization.
For us at Zircuit, this translates into lower fees, higher throughput, and more predictable network behavior. With Fusaka support already live, we’re excited to keep shipping on top of these improvements!
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