Fusaka upgrade: Ethereum has set Dec. 3, 2025 as the tentative mainnet activation for the Fusaka upgrade, phasing higher blob capacity to support rollups and lower fees while developers validate client stability and fix remaining bugs.
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Dec. 3, 2025 mainnet activation date set for Fusaka
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Blob capacity will increase in two phased steps (10/15 then 14/21 blobs per block) to reduce rollup fees.
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Testing exposed client and ckzg library issues; Devnet-6 and shadow forks planned before mainnet.
Fusaka upgrade: Ethereum schedules Dec 3, 2025 mainnet activation to boost blob capacity for rollups and lower fees — read the developer timeline and testing notes.
What is the Fusaka upgrade and when will it activate?
Fusaka upgrade is a phased Ethereum protocol upgrade designed to increase blob capacity for rollups and reduce transaction fees. Developers agreed on a target mainnet activation date of Dec. 3, 2025, pending successful Devnet-6 tests and final client releases.
How will Fusaka increase blob capacity for rollups?
Developers plan a two-step capacity increase to lower risk: initially raising blob limits to 10/15 blobs per block, then to 14/21 blobs per block. Blobs are temporary data packets used by rollups to post transaction data cheaply to Ethereum. Phasing reduces overload risk while monitoring network stability.
Why did developers move the Fusaka timeline forward?
Developers advanced the timeline to give rollups more blob space sooner, addressing rising scaling pressure and fee concerns. Testing on Fusaka Devnet-5 revealed software bugs and setup errors, but when stable, teams agreed to step increases in blob capacity to manage risk.
What testing revealed about client performance and bugs?
Fusaka Devnet-5 showed that the Prysm validator client struggled under high loads, producing orphaned blocks. Teams also identified and fixed a bug in the ckzg library used to verify blobs. A lighter ckzg implementation is being prepared to ease client upgrades.
Developer notes from researcher Christine Kim and comments from Ethereum researcher Justin Traglia informed the timeline adjustments. The Ethereum Foundation was noted as not immediately commenting on the call summaries.
When will further tests and releases occur?
Developer calls confirm an upcoming Devnet-6 to double-check blob capacity targets before public testnets and mainnet. Client teams will ship bundled releases for October testnet upgrades and run shadow forks ahead of deployment. Delays remain possible if new bugs appear.
How does Fusaka relate to prior upgrades?
Fusaka follows the Pectra upgrade (rolled out in May), which increased data capacity and raised staking limits. Pectra helped make Ethereum easier to use, while Fusaka focuses on sustaining rollup growth with faster blob capacity increases.
Frequently Asked Questions
Will Fusaka immediately reduce fees for rollups?
Fusaka phases in blob capacity increases designed to lower rollup calldata costs, but fee effects depend on rollup adoption and overall network demand. Phased increases aim to balance capacity with network stability.
Do node operators need to update software before Dec. 3, 2025?
Yes. Node operators should plan to install bundled client releases and participate in testnets and shadow forks to ensure compatibility before the Dec. 3, 2025 target activation.
Key Takeaways
- Fusaka activation date: Targeted for Dec. 3, 2025, pending tests and fixes.
- Phased blob increases: Planned steps (10/15 then 14/21 blobs per block) to support rollups and lower fees.
- Testing and client stability: Devnet-5 revealed Prysm and ckzg issues; Devnet-6, shadow forks, and bundled releases are scheduled to mitigate risks.
Conclusion
The Fusaka upgrade accelerates Ethereum’s roadmap for rollup capacity by phasing larger blob limits and enforcing rigorous testing before mainnet activation on Dec. 3, 2025. Node operators and rollup teams should engage in Devnet-6 and shadow forks to ensure a smooth transition and lower fees for users.
