What Is Ethereum Fusaka? 2025 Upgrade Explained

Ethereum's next major network upgrade, Fusaka, is scheduled for mainnet activation on December 3, 2025. While previous upgrades focused on transitioning to proof-of-stake or enabling basic Layer 2 scaling, Fusaka takes a different approach: it fundamentally changes how Ethereum handles data availability, preparing the network for enterprise-scale adoption while dramatically reducing costs for rollups.

The upgrade introduces 12 Ethereum Improvement Proposals (EIPs) across four focus areas: scaling, security and stability, functionality, and network optimization. But the headline feature is EIP-7594, Peer Data Availability Sampling (PeerDAS), which Tim Sun, Senior Researcher at HashKey Group, describes as having "the greatest impact on the Layer 2 ecosystem in this upgrade."

HashKey was one of the earliest investors in Ethereum and recently launched the Ethereum Application Guide with Ethereum co-founder Vitalik Buterin, giving Sun a front-row view of how infrastructure upgrades affect real-world adoption.

The technical changes in Fusaka might sound incremental, raising the block gas limit from 45 million to 150 million and introducing new data management techniques. But the implications are substantial: cheaper Layer 2 transactions, lighter node requirements, and a foundation for privacy-preserving enterprise applications that can finally compete on cost with traditional infrastructure.

When the Dencun upgrade introduced "blobs" (a data format specifically for Layer 2 rollups to post transaction information) in March 2024, it reduced Layer 2 data costs by roughly 90%. That was transformative. Transactions on Arbitrum and Optimism dropped from dollars to cents. But there was a constraint: validators still needed to fully download and verify all blob data, imposing high storage requirements on nodes.

PeerDAS changes that fundamentally. "Validators only need to sample a small portion of blob data to probabilistically verify its overall availability without storing the entire dataset," Sun explains. Instead of downloading complete blobs, validators randomly sample small pieces from different peers across the network. If the samples check out, the full data is provably available.

This isn't just an optimization. It's a different security model. Each validator now custodies only 1/8th of the blob data (distributed uniformly and randomly across the network), but any 50% of the data can reconstruct the whole. The probability of incorrect or missing data drops to cryptographically negligible levels (roughly one in 10^20 to one in 10^24). Meanwhile, theoretical blob capacity scales up to 8x current levels without proportionally increasing hardware requirements.

"For the Layer 2 ecosystem, this means a significant increase in data bandwidth and a higher scalability ceiling," Sun notes. "At the same time, the operational burden on nodes is greatly reduced, further strengthening decentralization."

The immediate effect: Ethereum can support far more rollup activity without validators needing enterprise-grade hardware. The long-term effect: Layer 2 protocols can scale to handle millions of transactions per second while still inheriting Ethereum's security guarantees.

But Fusaka isn't just about raw throughput. Two companion EIPs (7892 and 7918) improve the blob fee market and enable "blob-parameter-only" (BPO) forks, a mechanism to continuously increase blob count between major upgrades. Pre-Fusaka, the blob target was six per block. After activation, that number can increase sustainably based on network demand without waiting for coordinated hard forks.

This matters because Layer 2 growth is unpredictable. If adoption surges faster than expected, Ethereum can respond by incrementally raising blob capacity rather than forcing rollups to compete for limited space or wait months for the next major upgrade.

EIP-7918 addresses another subtle but important issue: ensuring blob fees remain meaningful price signals. Previously, if execution gas costs dominated, the blob fee auction could spiral down to 1 wei and stop reflecting actual congestion. The new mechanism pins a proportional reserve price under every blob, preventing the fee market from breaking during edge cases and ensuring Layer 2s pay at least a meaningful portion of the computational resources they consume.

Beyond scaling, Fusaka introduces a suite of security and stability improvements. EIP-7823 sets upper bounds for the MODEXP precompile (a built-in function for modular exponentiation used in cryptographic operations), preventing extreme inputs that could destabilize clients. EIP-7825 caps individual transactions at 16.7 million gas (roughly the size of pre-Fusaka average blocks), proactive protection against DoS attacks as the block gas limit rises. EIP-7934 limits RLP-encoded execution block size to 10 MiB, aligning with consensus layer constraints and preventing propagation issues.

These changes might seem technical, but they address real vulnerabilities discovered as Ethereum scales. "EIP-7823 and EIP-7934 define input sizes and execution block sizes," Sun explains. "These adjustments help mitigate risks such as client overload or network instability under extreme transaction scenarios. This not only strengthens Ethereum's long-term reliability but also reduces Layer 2 operating costs."

The upgrade also includes quality-of-life improvements for developers: a new CLZ (count leading zeros) opcode that makes certain arithmetic operations more efficient, deterministic proposer lookahead enabling preconfirmations (commitments from upcoming block proposers that transactions will be included), and a precompile for secp256r1 curve support that enables passkey-style signing using device-native security (Apple Secure Enclave, Android Keystore, hardware security modules).

That last feature matters for user experience. Wallets can now tap into the security infrastructure that billions of devices already use, eliminating seed phrases and enabling multi-factor authentication flows that feel like modern consumer apps rather than crypto-native complexity.

Privacy has been one of crypto's persistent challenges. Enterprises want blockchain's transparency and auditability, but they need confidentiality for sensitive business data. Zero-knowledge proofs offer a solution, but historically the computational costs have been prohibitive for most use cases.

Fusaka changes that. "The key change is that ZK-proof based privacy solutions now have the potential to reach commercially viable cost levels," Sun argues. "Since Fusaka allows validators to sample data instead of fully downloading it, privacy computation layers can be deployed more lightly. Enterprises no longer need to run expensive full nodes to achieve Ethereum-level security and data availability at lower costs."

This isn't theoretical. Sun points to real-world implications: "In the long term, this enables large-scale, real-world business applications to inherit Ethereum's security while gaining strong privacy protection. This represents a major breakthrough for enterprise adoption of Web3."

The combination of dramatically lower Layer 2 costs, lighter node requirements, and viable privacy infrastructure creates conditions for applications that couldn't exist on Ethereum previously. Supply chain tracking with confidential pricing. Healthcare data sharing with patient privacy. Financial settlement with regulatory compliance. These use cases require both scale and privacy, and Fusaka provides infrastructure for both.

The upgrade follows a careful rollout process: Holesky testnet (October 1), Sepolia testnet (October 14), Hoodi testnet (October 28), with mainnet targeted for December 3. Each testnet phase stress-tests performance and identifies edge cases before production deployment. The Ethereum Foundation is also running a four-week bug bounty with rewards up to $2 million, encouraging thorough security review before activation.

For users, Fusaka should mean faster transaction confirmations during network congestion and more predictable gas fees as Layer 2s benefit from increased capacity. For developers building on Layer 2, it means reliable, cheap data availability that scales with demand. For enterprises considering blockchain infrastructure, it means Ethereum can finally support privacy-preserving applications at commercially viable costs.

Fusaka isn't the end of Ethereum's scaling roadmap. It's a foundation. Together, all the changes position Ethereum to support applications that require both massive scale and strong guarantees, moving closer to the vision of a decentralized global settlement layer that works for everyone.

Learn much more in the link below:
https://ethereum.org/roadmap/fusaka/