What Is the Fusaka Upgrade: Ethereum's Next Hard Fork

Ethereum Fusaka Upgrade Overview

What Is the Fusaka Upgrade?

The Fusaka upgrade is a comprehensive network update (or "hard fork"— a change that isn't backward compatible) scheduled to activate on Ethereum's mainnet on December 3, 2025. This would mark Ethereum’s latest upgrade since the Pectra Upgrade which took place in May 2025.

Fusaka’s Name

Following Ethereum's naming convention, "Fusaka" combines two upgrade names: "Fulu" (for the consensus layer, named after a star) and "Osaka" (for the execution layer, named after the Japanese city that will host Devcon 2025, an Ethereum convention event). 

Where Fusaka Fits in Ethereum's Roadmap

To understand Fusaka's importance, it helps to see where it sits in Ethereum's evolution:

• The Merge (2022): Transitioned Ethereum from energy-intensive proof-of-work to efficient proof-of-stake

• Shanghai/Shapella (2023): Enabled validators to withdraw their staked ETH

• Dencun (March 2024): Introduced "blobs" (temporary data storage packets) that reduced Layer 2 fees by 90-95%.

• Pectra (May 2025): Increased blob capacity and improved validator flexibility.

• Fusaka (December 2025): Dramatically scales data availability through PeerDAS and prepares Ethereum for 100,000+ TPS.

Each upgrade builds on the previous one. Dencun introduced the concept of blobs — think of them as temporary storage containers where Layer 2 networks can post transaction data cheaply. Fusaka takes this concept much further by introducing a smarter way for the network to verify this data exists without every validator needing to download everything.

Core Technical Improvements Explained Simply

Fusaka includes approximately 12-13 Ethereum Improvement Proposals (EIPs — formal proposals for changes to Ethereum). While that sounds technical, the key improvements fall into a few understandable categories.

PeerDAS: Fusaka’s Main Feature

PeerDAS (Peer Data Availability Sampling, defined in EIP-7594) is Fusaka's headline feature and represents a fundamental shift in how Ethereum handles data.

The Problem It Solves: Currently, when Layer 2 networks like Arbitrum or Optimism post their transaction data to Ethereum (in those blob containers we mentioned), every validator needs to download the complete data to verify it's available. This creates a bottleneck — if blobs get too big or too numerous, validators need expensive hardware with high bandwidth to keep up.

The Solution: Create a system where network validators are not required to download entire blobs of data, but instead just need small samples of these blobs for verification. 

Imagine a library where instead of reading an entire book to confirm it's complete and undamaged, you could randomly check a few pages. If enough people check different random pages and they all look good, you can be confident the whole book is intact. That's essentially what PeerDAS does.

With PeerDAS, validators only need to download approximately 12.5% of the blob data — they sample random portions and share that information with peers. Through mathematical techniques called "erasure coding" (which adds redundancy to data, like a sophisticated backup system), the network can reconstruct the full data from just 50% of the pieces. This means:

• Validators need 85% less bandwidth compared to downloading everything.

• Storage requirements drop significantly for individual nodes.

• The network can safely support many more blobs without overwhelming validators.

• Home stakers can continue participating without needing enterprise-grade internet connections.

Think of it this way: instead of everyone at a concert recording the entire show, a few people record different parts, and if you need the full concert later, you can piece it together from everyone's recordings.

Block Gas Limit Increase: Enabling More Complex Transactions

Gas is Ethereum's measure of computational work — every transaction and smart contract operation consumes a certain amount of gas. The gas limit determines how much computation can fit in a single block.

EIP-7935 increases Ethereum's default block gas limit from approximately 36 million to 60 million gas units. This 67% increase means:

• More transactions can be processed on Ethereum's main network (Layer 1).

• Complex smart contracts have more room to execute without running into limits.

• Network throughput improves even before considering Layer 2 benefits.

However, bigger blocks mean validators must process more data. To make sure the network is not overwhelmed, Fusaka also introduces several safety measures such as a block size cap (EIP-7934) and a transaction gas cap (EIP-7825). 

EVM Improvements and New Features

The Ethereum Virtual Machine (EVM) is the computer that executes all smart contracts throughout Ethereum and its Layer 2s. Fusaka includes several enhancements:

EVM Object Format (EOF): Think of this as a cleaner, more efficient programming structure for smart contracts. It separates code from data more clearly, making contracts easier to validate and optimize. For developers, this means faster execution and fewer errors.

New Opcodes (EIP-7742): Opcodes are basic instructions the EVM can execute (like ADD, SUBTRACT, or STORE). Fusaka adds a CLZ (count leading zeros) opcode that makes certain cryptographic operations more efficient. While this sounds niche, it helps with tasks like verifying digital signatures and processing cryptographic proofs.

secp256r1 Support (EIP-7212): This adds support for a different type of digital signature that's commonly used in mobile devices and hardware security modules. Practically, this means you could eventually use your iPhone's Face ID or fingerprint sensor to interact with Ethereum apps instead of managing a seed phrase — making crypto more accessible and secure for everyday users.

Why Fusaka Matters: The Big Picture

Enabling True Layer 2 Scaling

The most significant impact of Fusaka is what it enables for Layer 2 rollups — separate blockchains like Arbitrum, Optimism, Base, and zkSync that bundle thousands of transactions together and post summaries to Ethereum for security.

Current State: After the Dencun upgrade in March 2024, Layer 2 fees dropped from $0.50-$3.00 to around $0.01-$0.10 per transaction — a massive improvement. However, these L2s are already filling up the available blob space during peak usage.

After Fusaka, Layer 2 networks will have:

• 3.5x more space to post transaction data.

• 40-60% lower costs as blob fees decrease due to increased supply.

• Capacity to handle 100,000+ transactions per second across the entire L2 ecosystem (compared to roughly 12,000 TPS estimates pre-Fusaka).

To put this in perspective, Visa processes about 65,000 TPS on average. Ethereum's Layer 2 ecosystem post-Fusaka could theoretically exceed this, while maintaining the security and decentralization of Ethereum's base layer.

The Blob Fee Reserve Mechanism

Fusaka also has several implications on transaction fees during periods of network congestion. EIP-7918 introduces a blob fee reserve system that changes how blob pricing works. 

Instead of blob fees fluctuating wildly based on immediate demand (like gas prices do), excess blob fees get stored in a "reserve." When demand spikes and blob fees rise rapidly, the reserve automatically releases fees back into circulation to smooth out price volatility. When demand is low, fees accumulate in the reserve.

What This Means:

• More predictable costs for Layer 2 networks.

• Better user experience as L2 fees become more stable.

Reduced Validator Requirements

For people running Ethereum validators (the computers that secure the Ethereum network by validating transactions), Fusaka brings welcome relief:

Bandwidth Reduction: PeerDAS cuts the amount of data validators need to download by approximately 85%. If a validator previously needed to download 750 MB of blob data per day, they'd now only need around 112 MB.

Storage Optimization: While validators still need to store blob data temporarily (blobs are kept for about 18 days), the ability to sample data means they don't need to store everything permanently.

Decentralization Benefits: Lower requirements mean more people can run validators from home without needing enterprise-grade internet connections. This strengthens decentralization — one of Ethereum's core values.

Impact of the Fusaka Upgrade

Regular ETH Holders

Even if you just hold ETH and occasionally make transactions, Fusaka impacts you:

Cheaper L2 Transactions: If you use Layer 2 networks for trading, NFTs, or DeFi, your transaction costs will decrease by an estimated 40-60%. That $0.05 transaction might drop to $0.02-$0.03.

Improved Network Performance: With higher throughput and more efficient data handling, the entire Ethereum ecosystem becomes smoother and more reliable.

DeFi Users

If you participate in decentralized finance — lending, borrowing, trading on DEXs, or providing liquidity:

Faster, Cheaper Interactions: Complex DeFi operations on Layer 2 networks will become more affordable. Yield farming strategies that were uneconomical at $0.10 per transaction might make sense at $0.02.

More Sophisticated Decentralized Applications: The increased gas limit and EOF improvements enable more complex smart contracts, potentially leading to innovative DeFi products that weren't previously possible.

Developers

For those building on Ethereum:

Improved EVM: The EOF enhancements make smart contracts easier to write, test, and optimize. Code separation improves security and reduces bugs.

New Tools: The CLZ opcode and secp256r1 support open up new possibilities, particularly for cryptographic applications and mobile-friendly wallet experiences.

Scalability Infrastructure: With blob capacity expanding, developers can build applications that would have been throttled by data availability constraints under the old system.

Layer 2 Networks

For teams running rollups like Arbitrum, Optimism, Base, or zkSync:

Increased Capacity: The ability to post more data to Ethereum means these networks can process more transactions without hitting bottlenecks.

Lower Operating Costs: As blob fees stabilize and capacity increases, the cost of settling to Layer 1 decreases, savings that can be passed to users.

Competitive Advantage: L2s that efficiently utilize the new blob space can offer the fastest and cheapest transactions, attracting more users and developers.

Validators and Node Operators

For those securing the network:

Lower Barriers to Entry: Reduced bandwidth requirements mean the cost to set up a network validator decreases, potentially increasing the number of validators and node operators throughout the network.

Simplified Operations: The improvements to network protocols and deterministic block proposer selection (knowing in advance when you'll propose blocks) make validator operations more predictable.

Fusaka’s Potential Market Impact

Institutional Interest

Institutional adoption of Ethereum has been growing, and Fusaka could accelerate this trend:

Infrastructure Maturity: Major upgrades that execute successfully without network disruptions demonstrate Ethereum's technical maturity — a key consideration for institutions managing billions in assets.

Competitive Positioning: By significantly improving scalability while maintaining security and decentralization, Fusaka helps Ethereum defend against competitors like Solana that have traditionally emphasized speed over decentralization.

Strategic Importance

Beyond short-term price movements, Fusaka represents a strategic milestone:

The Scalability Race: Competing blockchains like Solana, Avalanche, and newer L1s constantly improve their technology. Fusaka demonstrates Ethereum's ability to scale significantly while preserving decentralization.

Layer 2 Ecosystem Growth: With over 50% of DeFi value locked on Ethereum-related chains, scaling Layer 2s effectively expands Ethereum's addressable market without fragmenting liquidity.

Developer Retention: By consistently upgrading the EVM and providing better tools, Ethereum maintains its position as the preferred platform for serious developers, which drives long-term value.

What’s Next For Ethereum After Fusaka

The Road Ahead: Glamsterdam

After Fusaka, Ethereum's next major upgrade is tentatively called "Glamsterdam" (combining the star "Gloas" and "Amsterdam," the city that hosted Devconnect 2022). Glamsterdam is expected to arrive in 2026.

While specifics remain under discussion, the Ethereum roadmap continues with:

The Surge (ongoing): Further scalability improvements beyond Fusaka, potentially including full Danksharding (the complete vision of which PeerDAS is just the first step).

The Verge: Introducing Verkle Trees (partially included in Fusaka) to make nodes even lighter and enable "stateless clients" that can verify the chain without storing complete state.

The Purge: Simplifying the protocol by removing historical data and technical debt, making Ethereum easier to run and maintain.

The Splurge: Various improvements including account abstraction enhancements, MEV (miner extractable value) solutions, and cryptographic upgrades.

The Long-Term Vision

Ethereum's ultimate goal remains unchanged: become a global settlement layer that's:

• Scalable: Handle millions of transactions per second through Layer 2s

• Secure: Maintain robust security through thousands of independent validators

• Decentralized: Enable anyone to run a node or validator without prohibitive costs

Fusaka represents a major step toward this vision by proving that scalability and decentralization aren't mutually exclusive—you can have both through clever engineering like PeerDAS.

Conclusion

The Fusaka upgrade marks a pivotal moment in Ethereum's continued development. By introducing PeerDAS, increasing the gas limit, and implementing numerous smaller improvements, Fusaka transforms Ethereum from a blockchain that can support some Layer 2 activity into one that can sustain a massive ecosystem of scaling solutions processing hundreds of thousands of transactions per second.

For everyday users, this means cheaper transactions and more responsive applications. For developers, it means better tools and the infrastructure to build more ambitious products. For validators, it means lower barriers to participation and a more sustainable network to secure. And for Ethereum as a whole, it means defending its position as the leading smart contract platform while staying true to its decentralization principles.

This article is for educational and informational purposes only and should not be construed as financial advice. The cryptocurrency market is highly volatile and speculative. Ethereum upgrades involve complex technical changes that may not perform exactly as anticipated.