Foresight Ventures: Dencun upgrade is coming, which L2s have adopted?

8 min readMar 15, 2024

Author：Maggie@Foresight Ventures

TL;DR：

The Dencun upgrade is set to launch on March 13, 2024, with EIP-4844 about to go live. Danksharding stands as a core component of Ethereum’s roadmap, and this upgrade marks the first step towards its realization.
After Ethereum L2 adopts EIP-4844, transaction fees will significantly decrease, and the TPS on L2s will increase exponentially. Users will notice faster transaction speeds, lower costs, smoother experiences, and more responsive interactions. These L2s will able to support more complex and larger-scale DApp applications.
Adapting Optimistic rollups to EIP-4844 is simpler while adapting ZK rollups is more complex. Ethereum lacks precompiled contract support for the BLS12–381 elliptic curve, which poses challenges for some ZKP (Zero-Knowledge Proof) verifications, hindering the progress of ZK rollups in adopting EIP-4844.
The issue with elliptic curves can be addressed in two ways: 1. Waiting for Ethereum to precompile the BLS12–381 elliptic curve; 2. Employing an alternative proof method, utilizing BN254 precompiled contracts supported by Ethereum, to achieve the same objective.
Arbitrum, Optimistic, Starknet, zkSync, Scroll, Polygon zkEVM and the new L2 Morph are all integrating EIP4844. Among them, Arbitrum, Optimistic, and Starknet have announced plans to implement adaptations for EIP4844 following the Dencun upgrade. Meanwhile, Morph has pioneered the release of an innovative zkEVM adaptation solution, marking the first zkSNARK zkEVM adaptation for EIP4844.

1. The background of Dencun upgrade

In 2020, Ethereum released the new roadmap “A rollup-centric ethereum roadmap”， Vitalik’s subsequent publication of ‘Endgame’ the following year, outlined Ethereum’s overarching direction: optimizing Ethereum infrastructure to support Rollups.

Danksharding is designed to enhance Ethereum’s scalability by implementing sharding techniques and makes Ethereum a better DA layer. This will significantly reduce transaction fees on Layer 2, boost Rollup’s transactions per second (TPS), and facilitate substantial scaling of the Ethereum network.

Until this year, the Ethereum Dencun upgrade was finally launched on March 13, 2024, with EIP4844 set to go live. This hard fork can be seen as the first step towards implementing Danksharding for Ethereum, marking a pivotal milestone in Ethereum’s core roadmap.

2. How does the Dencun upgrade benefit L2?

EIP4844 introduces a new transaction type called blob-carrying transactions. Each blob-carrying transaction can ‘carry’ a list of Blobs. A Blob is a data packet, approximately 125 KB in size. Blobs are stored in Ethereum nodes for a short duration, only 4096 epochs, slightly over 18 days.

2.1 L2 transaction fees are expected to significantly decrease.

Since blobs are not permanently stored, they offer a larger and more cost-effective space than block space. Blobs can store 10x more data than calldata under the same gas consumption. Rollups adapted to EIP4844 can facilitate L2 to store transaction batches in blobs, leading to a significant reduction in transaction costs.

2.2 A multiplicative increase in L2 TPS.

Currently, each block targets 3 blobs, with a maximum allowance of 6 blobs. The block size is only 90KB, while each blob is approximately 125 KB. Introducing blobs essentially multiplies the available space within the block for storing rollup data, resulting in a multiplicative increase in rollup’s TPS. Moreover, the proposal put forward by Toni and Vitalic in “On Increasing the Block Gas Limit” suggests achieving smaller and less variable block sizes in the future by increasing the prices of both block gas limits and non-zero calldata bytes. This would allow for more blobs to be added, consequently increasing storage space.

After Ethereum L2 adapts EIP-4844, end users can expect faster transaction speeds, lower costs, smoother experiences, and more responsive interactions. Additionally, there will be more complex and larger-scale DApp applications on these L2 solutions.

2. How do L2 rollups adapt to EIP4844?

How do L2 solutions adapt to EIP4844? Let’s break it down for Optimistic rollups and ZK rollups separately.

Adapting optimistic rollups to EIP4844

Optimistic rollups use fraud proofs as a safeguard mechanism to maintain the integrity and security of the system. These proofs act as a check against potential malicious behavior or incorrect state transitions within the rollup chain. Nodes initially assume that state transitions are correct unless someone submits a fraud-proof within a specified timeframe, proving that previously submitted state transitions are incorrect. This results in the reversal of the state transition.

Adapting optimistic rollups to EIP4844 is relatively simpler compared to ZK rollups. The adaptation can be achieved by simply submitting all L2 transaction batches through blob-carrying transactions to L1. Then, adjusting fraud-proof mechanisms to adapt EIP4844.

1.L2 transaction batch submission: Using blob-carrying transactions to submit L2 transaction batches. The payload of Blob-carrying transactions is rlp([tx_payload_body, blobs, commitments, proofs]) , where:

tx_payload_body — is the TransactionPayloadBody of standard EIP-2718 blob transaction
blobs — list of Blob items
commitments — list of KZGCommitment of the corresponding blobs
proofs — list of KZGProof of the corresponding blobs and commitments

2.Fraud proof adjustment.

The prover and challenger engage in multi-round interactions to identify the point of dispute.
The point of dispute is then submitted to L1 for adjudication. Adapting to EIP4844 may also require proving that the data related to this dispute is stored in a specific blob.
Since blob data is typically deleted after approximately 18 days, the challenge period must end before this deletion, a requirement that current optimistic rollups meet. Generally, the challenge period does not exceed 7 days.

Adapting ZK rollups to EIP4844

ZK rollups use Zero-Knowledge Proofs (ZKPs) to ensure the correctness of L2 state transitions. Adapting ZK rollups to EIP4844 is relatively more complex compared to optimistic rollups.

1.L2 transaction batches submission: this step is similar to optimistic rollup, using blob-carrying transactions.

2.ZK proof submission: in addition to providing proofs for state transitions, adapting to EIP4844 also requires an additional proofing process. Specifically, it’s necessary to prove that the blob commitment corresponds to the transaction batch, ensuring the correctness of the input for state transition proofs.

To illustrate: the ZK circuit for state transitions can generate proofs for the computation process a + a = b. When you provide (a=1, b=2) and (a=2, b=4), the proofs generated are valid for both cases. it’s essential to provide proof that the input provided was (a=1, b=2) and not (a=2, b=4).

This wasn’t necessary before adapting to EIP4844 since data was directly stored in calldata. With EIP4844, Blob data can’t be directly read from smart contract, so we need a new circuit to prove the data.

Implementing this proof mechanism is easier with STARK-based ZK Rollups (such as Starknet) compared to those using SNARKs due to the challenge posed by elliptic curve mismatch. EIP4844’s blob commitment utilizes the BLS12–381 curve, whereas ETH’s precompiled contracts only support BN254, making it difficult to directly verify blob commitments in smart contracts.

3.Some zk rollups using SNARKs need to address the challenge in contract verification of ZKPs due to elliptic curve mismatch.

Waiting for Ethereum to support BLS12–381 precompiled contracts will be time-consuming.
Adopting an alternative proofing method. Designing new circuits using the BN254 elliptic curve supported by precompiled contracts. Currently, we see Morph employing this method, making it the first zkEVM solution to adapt to EIP4844. See “Morph’s solution to EIP-4844 zkEVM integration”.

4. Which L2 rollups have adapted to EIP4844?

Adapting optimistic rollups to EIP4844 is relatively straightforward.

Arbitrum is scheduled to launch the Arb OS20 upgrade on March 14th to implement EIP changes for the Dencun upgrade (Article link). Arbitrum is a Stage 1 Rollup, requiring adaptation of transaction submission and fraud proofs to EIP4844, offering relatively high security.
Optimism completed the adaptation with the launch of the Ecotone upgrade on March 14th (Article link). As a Stage 0 Rollup, the Optimistic rollup currently lacks fraud proofs, making adaptation easier but with lower security. After the adaptation, all superchain networks within the Op ecosystem will benefit from EIP-4844.

In ZK rollups, the difficulty of adaptation varies between those using STARKs and those using SNARKs.

a) Adapting STARK-based rollups to EIP4844 is simpler, with Starknet being a representative example.

Starknet has announced plans to implement adaptation to EIP4844 after the Dencun upgrade (Article link).
zkSync has transitioned from SNARKs to STARKs with the Boojum upgrade in preparation for EIP4844 adaptation. Boojum is a STARK-based proof system. (Article link)

b) Adapting SNARK-based rollups is relatively complex.

Polygon zkEVM is expected to launch the Feijoa upgrade in May, adapting to EIP-4844 (Article link).
Scroll published an article last year outlining its approach to adapting to EIP4844 (Article link).
Notably, Morph, an Optimistic ZK Rollup, was the first to propose a solution for adapting zkSNARK zkEVM to EIP4844, making it the first zkSNARK zkEVM rollup to complete EIP4844 adaptation (Article link). Optimistic ZK Rollup combines the efficiency of Optimistic rollup with the reliability of ZK proofs. It optimistically trusts the results submitted by the Sequencer but allows challengers to question the results. Only when a challenge is initiated will the prover generate ZK proofs to demonstrate the correctness of the execution results.

In summary, these L2 solutions will gradually adapt to EIP4844, thereby becoming faster, more cost-effective, and better equipped to support large-scale Dapps.

About Foresight Ventures

Foresight Ventures is dedicated to backing the disruptive innovation of blockchain for the next few decades. We manage multiple funds: a VC fund, an actively-managed secondary fund, a multi-strategy FOF, and a private market secondary fund, with AUM exceeding $400 million. Foresight Ventures adheres to the belief of “Unique, Independent, Aggressive, Long-Term mindset” and provides extensive support for portfolio companies within a growing ecosystem. Our team is composed of veterans from top financial and technology companies like Sequoia Capital, CICC, Google, Bitmain and many others.

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