Ethereum core developers have set December 3, 2025 as the tentative mainnet activation date for the network’s next major hard fork, codenamed Fusaka, which is designed to improve scalability and efficiency.
The upgrade was confirmed during ACDC developer call #165 and will roll out across three public testnets, Holesky (Oct. 1), Sepolia (Oct. 14), and Hoodi (Oct. 28), before the December launch. Developers are expected to reconfirm final activation times and epoch numbers closer to the rollout.
Important decisions were made on today's Ethereum developer call, ACDC #165. Developers confirmed the public testnet schedule and BPO hard fork schedule for Fusaka.
— Christine D. Kim (@christine_dkim) September 18, 2025
Let's get into it. pic.twitter.com/mNrYMYyDj2
Phased blob capacity expansion
While Fusaka itself activates in early December, its most significant change, increased blob data capacity, will arrive in two follow-up phases:
- December 17: Blob capacity expands to 10 target / 15 maximum.
- January 7, 2026: Capacity rises further to 14 target / 21 maximum.
Ethereum researcher Christine D. Kim noted that these changes would more than double blob capacity, building on growth since the Dencun upgrade in March 2024. At present, average blob counts per block are around 5.1, up from 0.9 in March 2023, according to Dune Analytics.
Blob Parameter Only (BPO) forks govern these increases. They require no client‑side software changes, as they only adjust network parameters for blob usage.
Technical features of Fusaka
- PeerDAS (Peer Data Availability Sampling): Allows validators to verify large datasets, or “blobs,” by sampling small portions rather than downloading entire files. This reduces costs and resource demands for nodes, improving decentralization and helping Layer‑2 rollups scale.
- Gas improvements: Developers have discussed increasing Ethereum’s gas limit from 30 million to as high as 150 million, with proposals emerging under EIP‑7935 and others. Current consensus may land lower, but throughput capacity increases remain a priority.
- EVM performance: Incremental optimizations will improve smart contract execution speed.
- Verkle Trees: Expected to reduce proof sizes, making on‑chain data storage more efficient.
- Bounded fees for blob transactions: EIP‑7918 will introduce more predictable pricing for data‑heavy applications.
Ethereum’s EVM Object Format (EOF) and other more ambitious changes have been deferred to future updates like Glamsterdam in 2026 to reduce complexity.
Security and testing
To support the rollout, the Ethereum Foundation has launched a four‑week audit contest with up to $2 million in rewards for developers who find vulnerabilities in Fusaka’s codebase.
Node operators have deadlines in late September through early November to ensure compatibility before mainnet launch. Each of the testnets will replicate the full blob expansion sequence before December.
Market and protocol context
The Fusaka launch follows the Pectra upgrade in May 2025, which raised validator staking limits, introduced account abstraction, and improved Layer‑2 efficiency.
The timing coincides with pressures in Ethereum’s validator ecosystem: more than 2.6 million ETH (≈ $12 billion) recently entered the exit queue, leading to wait times of over 40 days. The long delays have spurred debate. Vitalik Buterin defended the exit mechanism as essential for security, while Galaxy Digital’s Michael Marcantonio argued the queue has become “troubling.”
Regulatory and adoption backdrop
Ethereum’s scaling roadmap faces scrutiny amid growing institutional adoption and regulatory attention. Firms such as VanEck have forecast that Layer‑2 ecosystems could reach $1 trillion market cap within six years. Meanwhile, policymakers are increasingly debating how to regulate transaction data availability and cross‑chain interoperability.
What Fusaka means for Ethereum
If successful, Fusaka will:
- Reduce node resource requirements, supporting further decentralization.
- Enable higher throughput for rollups through increased blob capacity.
- Lay groundwork for future upgrades like Glamsterdam, which may cut block times and implement the long‑planned EVM Object Format.
But challenges remain. Network fragmentation, validator queue backlogs, and regulatory scrutiny will continue to influence Ethereum’s trajectory. Fusaka represents an infrastructural leap forward, but not a complete solution to the network’s scaling pressures.
Anastasiia G
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