Ethereum's Biggest Upgrade Ever Ships

The Fusaka upgrade, which went live on December 3, 2025, is Ethereum's second major hard fork of the year, following the Pectra upgrade in May 2025. This signals a new, faster development pace, shifting from one major upgrade per year to a "twice-a-year" rhythm. The name itself combines "Fulu" for the consensus layer and "Osaka" for the execution layer, named after the city hosting Devcon 2025. PeerDAS is a practical implementation of a theoretical concept called Data Availability Sampling (DAS). Instead of every network node downloading all data, they can confirm its availability by checking small, random samples. This mechanism builds on the "blob" data structure introduced in the March 2024 Dencun upgrade, unlocking its full scaling potential by allowing more blobs per block. The move to a unified binary tree structure under EIP-7864 is a fundamental overhaul of Ethereum's state. Proposed by Vitalik Buterin among others, it replaces the original, more complex hexary Patricia tree. This new structure is designed to be more friendly to zero-knowledge proofs (SNARKs), which are a bottleneck for scalability. This state tree change has tangible benefits beyond proofs, potentially saving over 10,000 gas for certain transactions. By merging account data, code, and storage into a single tree, frequently accessed data can be grouped together, reducing the work needed to process transactions. This proposal gained traction over the previously planned Verkle trees partly due to concerns about the latter's vulnerability to quantum computing. The upgrade also adjusts the network's capacity limits, raising the block gas limit to a target of 60 million. To prevent a single large transaction from consuming an entire block, a new transaction gas limit cap was also introduced as a security measure against denial-of-service attacks. These technical changes solidify Ethereum's "rollup-centric roadmap," where the main blockchain primarily acts as a secure settlement layer. Layer 2 networks like Arbitrum, Base, and Optimism process the bulk of transactions and post summaries to Ethereum, with Fusaka's data capacity boost expected to lower L2 fees by 40-60%. Despite the milestone, Ethereum co-founder Vitalik Buterin noted that key challenges remain, including the base layer's sequential transaction processing and centralization risks from block builders. He frames Fusaka as a foundational step for the next two years of refinement. Looking ahead, the next upgrade is named Glamsterdam, planned for 2026. It will continue the work on scaling and network efficiency. Beyond that, a conceptual "strawmap" outlines a series of smaller, more focused upgrades through 2029, targeting goals like statelessness and further account abstraction improvements.