Key Takeaways
The Ethereum Cancun-Deneb (Dencun) upgrade launched on March 13, 2024, introducing proto-danksharding to the Ethereum network.
Proto-danksharding (EIP-4844) introduced blob-carrying transactions, which store temporary data on-chain for approximately 18 days before pruning, significantly cutting fees for Layer 2 rollups.
After Dencun went live, transaction fees on major Layer 2 networks dropped by as much as 80-99%, making Ethereum-based applications more affordable for everyday users.
The upgrade also included EIP-1153, EIP-4788, and EIP-6780, improving block space usage, communication between Ethereum's consensus and execution layers, and smart contract security.
Dencun is a step toward full danksharding, a longer-term goal on the Ethereum roadmap. The Pectra upgrade followed in May 2025, with the Fusaka upgrade next in line.
Introduction
The Ethereum Cancun-Deneb upgrade, commonly called Dencun, is a set of protocol improvements that went live on the Ethereum mainnet on March 13, 2024. Its main goal was to reduce the cost of Layer 2 rollups by introducing a new way to store transaction data temporarily on-chain, known as proto-danksharding.
Before Dencun, Layer 2 networks had to post transaction data to Ethereum's main chain as calldata, which is stored permanently and is relatively expensive. Dencun replaced this with blobs: large packets of data that nodes only need to keep for about 18 days before pruning them. This change cut the storage cost for Layer 2 networks dramatically.
The upgrade also included several smaller improvements targeting smart contract security, interoperability, and on-chain data efficiency. Together, these changes make Ethereum's execution layer faster, cheaper, and better prepared for future scaling.
Understanding the Ethereum Cancun Upgrade
The Cancun part of the Dencun upgrade focuses on the execution layer (Layer 1 of Ethereum). It bundles four Ethereum Improvement Proposals: EIP-4844, EIP-1153, EIP-4788, and EIP-6780.
EIP-4844 is the centerpiece. It introduces proto-danksharding and blob-carrying transactions, which are discussed in more detail below. EIP-1153 adds transient storage opcodes (TSTORE and TLOAD) that persist only for the duration of a single transaction rather than across blocks. This reduces gas costs for common smart contract patterns such as reentrancy locks, improving efficiency without increasing permanent storage. EIP-4788 exposes the Beacon Chain block root to the execution layer, improving communication between Ethereum's own consensus layer and execution layer. This enables better trust-minimized communication between the two halves of the protocol without relying on external oracles. EIP-6780 restricts the SELFDESTRUCT opcode, reducing the risk of smart contracts being deleted unexpectedly and improving the security of user funds.
The Deneb half of the upgrade addressed the consensus layer (Ethereum's proof-of-stake system) with complementary changes. Together, Cancun and Deneb form a single coordinated release that strengthened both halves of the Ethereum protocol.
Danksharding and Proto-Danksharding
Full danksharding is a long-term sharding design for Ethereum, named after researcher Dankrad Feist. Unlike earlier sharding proposals that split the network into many independent shards each with their own block proposers, danksharding uses a single block proposer across all shards and focuses on data availability rather than execution. This simplifies coordination while enabling high throughput.
Proto-danksharding, introduced by EIP-4844, is an intermediate step. It does not implement the full danksharding design but adds the blob transaction type and the data structures needed for the eventual full rollout. Think of it as laying the foundation before building the house.
Blob-carrying transactions
Blob-carrying transactions are the new transaction type introduced by EIP-4844. A "blob" is a large packet of binary data attached to a transaction. Blobs are cheaper to store than calldata because they use a separate fee market and are only kept by Ethereum nodes for approximately 18 days. After that window, blobs are pruned from the network.
This pruning is safe because Layer 2 rollups typically have a withdrawal period of around seven days, meaning all necessary dispute windows close well before the blobs are deleted. Cryptographic proofs ensure that historical blob data can still be verified even after the raw data is no longer available on every node.
Impact of the Dencun Upgrade
Shortly after Dencun activated in March 2024, the real-world impact on Layer 2 fees was significant. Networks built on rollup technology reported fee reductions of 80-99% compared to pre-Dencun levels. Transactions on these networks that previously cost several cents dropped to fractions of a cent for common operations.
This improvement made Ethereum-based applications noticeably more accessible, particularly for users with smaller budgets who had previously found gas fees prohibitive. Activity on Layer 2 networks increased following the upgrade, reflecting greater affordability.
At the same time, the upgrade validated Ethereum's rollup-centric scaling roadmap. By making rollups significantly cheaper to operate, Dencun reinforced the approach of offloading execution to Layer 2 networks while using Ethereum mainnet for security and data availability.
Potential Risks of the Ethereum Cancun Upgrade
Dencun also carried implementation risks. Any protocol upgrade of this complexity requires extensive testing, and there were concerns about how existing smart contracts would respond to the new opcodes and transaction types. The Ethereum development community ran multiple testnets before the mainnet launch to identify and address compatibility issues.
The restriction of SELFDESTRUCT through EIP-6780 was another area requiring careful handling, as some existing contracts relied on this opcode. EIP-6780 did not fully remove SELFDESTRUCT but limited when it can be used, reducing risk while preserving backward compatibility.
What's Next After Dencun?
The Pectra upgrade (Prague-Electra) followed Dencun as the next major Ethereum hard fork, launching on May 7, 2025. Pectra focused on improvements to the validator experience, account abstraction, and blob capacity increases, building directly on the infrastructure Dencun put in place.
Looking further ahead, the Fusaka upgrade (Prague-Osaka) is the next major Ethereum hard fork in development as of mid-2026. Fusaka is expected to include PeerDAS (Peer Data Availability Sampling), a significant step toward full danksharding that goes beyond what Dencun delivered. PeerDAS distributes the task of storing and serving blob data across a larger set of network participants, reducing the burden on individual nodes and enabling a substantial increase in blob throughput.
Full danksharding remains on the Ethereum roadmap as part of the "Surge" phase, which targets eventual throughput of 100,000 or more transactions per second across the network. Dencun's proto-danksharding was a critical early step in that journey, establishing the infrastructure and data structures that subsequent upgrades continue to build upon.
FAQ
What is the Ethereum Cancun upgrade?
The Ethereum Cancun upgrade, combined with the Deneb consensus layer update, forms the Dencun hard fork. It launched on March 13, 2024. Its main change was the introduction of proto-danksharding via EIP-4844, which added blob transactions to cut fees for Layer 2 networks.
What is proto-danksharding?
Proto-danksharding is an intermediate implementation of the full danksharding design. It adds blob-carrying transactions to Ethereum, allowing Layer 2 rollups to post their transaction data as temporary blobs rather than permanent calldata. This reduces Layer 2 operating costs significantly.
How did Dencun affect Ethereum gas fees?
Dencun primarily reduced fees on Layer 2 networks rather than Ethereum mainnet directly. After the upgrade activated, major Layer 2 rollups reported fee reductions of 80-99%. Users transacting on these networks saw costs drop from several cents per transaction to fractions of a cent.
What are blob transactions?
Blob transactions are a new transaction type introduced by EIP-4844. Each blob carries a large packet of binary data that is stored on-chain by Ethereum nodes for approximately 18 days before being pruned. This temporary storage model is far cheaper than permanent calldata storage, making it cost-effective for rollups to post their data to Ethereum.
What came after the Cancun-Deneb upgrade?
The Pectra upgrade (Prague-Electra) launched on May 7, 2025, introducing improvements to validators, account abstraction, and increased blob capacity. The Fusaka upgrade is the next major hard fork in development as of mid-2026, expected to include PeerDAS as a further step toward full danksharding.
Closing Thoughts
The Ethereum Cancun-Deneb upgrade marked a meaningful step forward in Ethereum's scalability roadmap. By introducing proto-danksharding and blob transactions, it made Layer 2 networks substantially cheaper to use, bringing Ethereum closer to its goal of supporting high transaction volumes at low cost. Dencun demonstrated that the rollup-centric scaling approach can deliver tangible improvements, and the lessons from its deployment continue to inform subsequent upgrades like Pectra and the longer-term path toward full danksharding.
Further Reading
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