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Ethereum’s Fusaka upgrade is tentatively slated for Dec. 3 on mainnet, aiming to expand data capacity for rollups while aiming to preserve decentralization and security.
Fusaka Incoming
Ethereum core contributors set the target after aligning on testnet steps and parameters at the All Core Devs – Consensus (ACDC) #165 meeting, with discussion centered on scope and timing. The plan stages feature readiness on devnets, then across three public testnets, before a mainnet fork about a month later, contingent on stable results.
Fusaka concentrates on scalability with a phased “blob” expansion plan called Blob Parameter Only (BPO) forks. The first phase lifts the maximum blobs per block to 15 in December, then to 21 in January, doubling today’s ceiling and widening bandwidth for Layer two (L2) rollups to post data. These parameters roll out without new client code, limiting operational churn.
The release also introduces peer data availability sampling (PeerDAS), allowing nodes to verify block data by sampling small pieces instead of downloading everything. Combined with the larger blob budget, the mechanism is expected to cut costs for rollups and decentralized finance (DeFi) while easing hardware pressure on full nodes.
ACDC #165 detailed live testing across multiple devnets, including stress runs at varying blob caps and toggling builder relays to surface edge cases. The group outlined a code freeze, coordinated client releases, and a testnet cadence that spaces forks and BPOs so engineers can observe behavior between steps.
Alongside performance work, a security competition offers up to $2 million in bounties focused on Fusaka-era code paths. Organizers encouraged frequent triage to avoid duplicate reports as clients publish updates, and flagged dependency hygiene in cryptography and>
Importantly, Fusaka does not change user-facing features; it is a protocol-layer refit meant to raise throughput and lower data fees on L2s. Users may feel the impact as cheaper, faster transactions on rollup apps once capacity gains flow into pricing.
The roadmap also anticipates continued work on execution- and consensus-layer refinements that complement Fusaka, including research on block access lists and proposer-builder separation variants. Those pieces are staged carefully to avoid distracting from the goal of shipping on schedule.
If testing proceeds as planned, the tentative Dec. 3 fork will mark a milestone in Ethereum’s multi-year drive to scale while keeping the network accessible to ordinary node operators — a balance engineers say remains central. Final readiness checks remain the last gate.