Ethereum activated the Fusaka network upgrade on December 3, 2025, at mainnet epoch 411392, corresponding to slot 13,164,544 and 21:49:11 UTC. The coordinated hard fork joined Osaka changes on Ethereum’s execution layer with Fulu changes on its consensus layer. Contemporaneous reporting said the fork finalized roughly 15 minutes after activation, indicating that upgraded clients had converged on the new rules.
Fusaka mattered because it changed how Ethereum could expand the data capacity used by layer-two rollups without requiring every node to download every piece of that data. It was Ethereum’s second major code change of 2025, after Pectra, and its central feature—Peer Data Availability Sampling, or PeerDAS—was infrastructure for the network’s rollup-centered scaling strategy rather than a promise of an immediate price or fee outcome.
PeerDAS changed the data burden
Rollups execute transactions away from Ethereum’s base layer and publish compressed data back to Ethereum in temporary objects called blobs. Before PeerDAS, nodes verifying availability handled complete blobs. EIP-7594 instead divides erasure-coded blob data into cells and distributes custody across column subnets. Nodes sample portions from peers; the specification says a node can reconstruct the data matrix after obtaining at least half of its columns.
The design sought to break the direct link between higher network-wide blob capacity and the bandwidth burden on each individual node. Under the event-day parameters described in EIP-7594, a node’s local availability check required one-eighth of the total data. That did not mean Ethereum increased blob limits eightfold on December 3. Fusaka activated the sampling machinery while the target and maximum remained six and nine blobs per block.
That distinction was institutionally important. Rollup operators gained a path to more Ethereum data capacity, while validators and infrastructure providers received a staged deployment instead of an immediate jump to the largest planned settings. Lower layer-two fees were a design objective, not an event-day measurement or guaranteed result; actual fees would continue to depend on demand, blob pricing and rollup behavior.
A staged capacity plan
Fusaka introduced Blob Parameter Only forks, a configuration mechanism defined by EIP-7892. It allowed later forks to change the blob target, maximum and fee-update fraction without bundling unrelated protocol code changes into another named upgrade.
As scheduled on December 3, the first parameter-only fork was due on December 9, 2025, raising the target and maximum from six and nine to 10 and 15. A second was scheduled for January 7, 2026, raising them to 14 and 21. Those were future steps on the event date, not completed Fusaka outcomes.
The upgrade also bundled safeguards and usability work. It capped gas consumed by a single transaction, repriced and bounded resource-intensive modular-exponentiation operations, added deterministic proposer lookahead, imposed an execution-block size limit, and added native support for the secp256r1 signature curve used by common secure hardware and passkey systems. Its configuration also set a 60 million default gas limit, supporting additional base-layer capacity while leaving block production subject to network rules and validator behavior.
What was known on December 3
The defensible event-day conclusion was that Ethereum had completed a coordinated rules change and installed the foundation for staged data-capacity growth. PeerDAS reduced the amount of blob data an individual node needed for an availability check, but the larger blob limits had not yet activated. No reviewed event-day evidence establishes a resulting percentage reduction in user fees, a transaction-throughput gain, or a causal effect on ether’s market price.
Later confirmation
On December 9, 2025, an Ethereum Foundation institutional note described Fusaka as live and stable and said the network maintained continuous uptime through the upgrade. That later statement supports successful activation, but it was not available at the close of the December 3 event record and does not convert the upgrade’s projected economic benefits into measured event-day results.
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