What is the Fusaka upgrade?

The Fusaka upgrade is an Ethereum hard fork that went live on mainnet on December 3, 2025, at 21:49 UTC. Its name joins Osaka, the execution layer upgrade, with Fulu, the consensus layer upgrade named after a star. Its main goal was to give layer 2 networks much more room to post data to Ethereum, which helps keep their fees down.

What is PeerDAS?

PeerDAS (EIP-7594) adds data availability sampling to Ethereum. Rollups post their transaction data to Ethereum in "blobs". Before Fusaka, every node downloaded every blob, so bandwidth limited how many blobs the network could handle.

With PeerDAS, blob data is extended with extra encoded copies so the original can be rebuilt from any half of it. The extended data is split into 128 columns, and each regular node keeps only a handful of them. Nodes then check small random samples against cryptographic commitments in each block. Many successful checks give strong confidence that all the data is available without anyone storing all of it. ethereum.org calls this the biggest scaling change since blobs were introduced.

What else changed in the Ethereum Fusaka upgrade?

Fusaka also added blob-parameter-only forks, small pre-planned changes that raise blob capacity without a full named upgrade. The first, BPO1, raised the blob target from 6 to 10 on December 9, 2025, and BPO2 raised it to 14 on January 7, 2026.

Other changes include:

• a default block gas limit of 60 million, up from 45 million
• a cap of about 16.7 million gas on any single transaction
• built-in support for the secp256r1 signature curve, used by passkeys and phone secure chips, which helps account abstraction wallets
• a limit of 10 MiB on execution block size, and support for nodes dropping pre-Merge history to save disk space

Fusaka did not change anyone's ETH. ethereum.org says balances stayed the same and holders did not need to act. It warns that anyone telling you to "upgrade" your ETH is trying to scam you. Fusaka aimed to lower layer 2 fees by adding blob space. It did not directly cut fees on Ethereum's main layer. Node operators and stakers did need to update their client software.

What comes after Fusaka?

The next named upgrade is Glamsterdam, which combines the Amsterdam execution changes with the Gloas consensus changes. ethereum.org describes two main features. Enshrined proposer-builder separation moves block building handoffs into the protocol itself. Block-level access lists let validators process transactions in parallel. As of its September 2026 update, ethereum.org listed Glamsterdam as testing on devnets, with a Sepolia test network fork on October 6, 2026 and a mainnet target of Q4 2026. No mainnet date had been confirmed. How these upgrades fit into the wider network is covered in what is Ethereum.