Ethereum’s core developers have mapped out a launch window for the long-anticipated Fusaka upgrade, with mainnet activation penciled in for Dec. 3.
The draft schedule, shared during the Sept. 17 All Core Developers’ Call (ACDC), still requires final confirmation, but it signals growing momentum toward one of Ethereum’s most significant technical overhauls.
The rollout will begin on test networks in stages. Holesky is set to upgrade on Oct. 1, followed by Sepolia on Oct. 14 and Hoodi on Oct. 28. Provided these rehearsals run smoothly, the changes will be ready to migrate onto Ethereum’s main network in December.
Phased Blob forks
Christine Kim, former research vice president at Galaxy Digital, emphasized that the network developers will continue refining dates, epochs, and timing over the coming weeks.
She added:
“They also agreed that based on some preliminary analysis on Fusaka Devnet-5, blob capacity should more than double over the two weeks following Fusaka activation.”
Blobs, introduced through EIP-4844, are temporary on-chain data containers that allow Layer 2 rollups to post transaction data to Ethereum at a lower cost. Unlike permanent call data, blobs expire after roughly two weeks, helping to reduce storage demands while maintaining data integrity.
This mechanism is designed to lower costs for rollups and improve Ethereum’s scalability.
To minimize risks, Ethereum developers agreed to gradually roll out via Blob Parameter Only (BPO) forks. So, instead of raising blob capacity in a single step, thresholds will be increased in phases.
As a result, the first BPO fork, expected Dec. 17, will raise blob targets from 6/9 to 10/15. A second fork on Jan. 7, 2026, will push those limits to 14/21.
Meanwhile, Fusaka’s impending rollout was announced just days after the Ethereum Foundation launched a $2 million security contest. The initiative, hosted on the Sherlock testnet from Sept. 15 to Oct. 13, incentivizes researchers to identify vulnerabilities in the upgrade.
To encourage early participation, findings submitted in the first week earn double points, while submissions in the second week qualify for a 1.5x multiplier.
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