EIP-4844: Blob Transactions Cut Rollup Costs

Key Takeaways

• EIP-4844 blob transactions give rollups a cheap data lane separate from regular Ethereum gas.
• Blobs target 3 per block and cap at 6, and are pruned after about 18 days.
• The common mistake is expecting blob data to be stored on Ethereum permanently.
• Cheaper data posting flows through to lower Layer 2 fees for everyday users.

What EIP-4844 Blob Transactions Are

Rollups must publish their transaction data to Ethereum so anyone can verify or rebuild the rollup's state. Before EIP-4844, they posted this data as calldata, which competed for the same gas as everything else and was stored forever, making it costly.

EIP-4844, live since the March 2024 Dencun upgrade, introduced blobs. A blob is a large packet of data attached to a block through a new transaction type. Blobs are not accessible to smart contracts and they are automatically deleted after a fixed period, which makes them far cheaper than calldata for the rollup use case.

The Intuition

Rollups do not need their raw data to live on Ethereum forever. They need it available long enough for anyone to check the rollup or reconstruct its state. After that, the data can be dropped.

EIP-4844 matches the storage to the need. Blobs stay available for about 18 days, plenty of time for verification and fraud-proof windows, then they are pruned. Because blobs use their own fee market, heavy rollup data demand does not directly bid up ordinary Ethereum gas, and rollups get a cheap, dedicated channel. The savings show up as lower Layer 2 transaction fees.

Separating the two fee markets also makes pricing fairer to each use. A wallet sending a simple transfer should not have to outbid a rollup posting a large data batch, and a rollup should not pay the premium of permanent storage for data it only needs briefly. By giving each its own lane and its own price, the network can serve both without one crowding out the other, at least until blob demand itself approaches the cap.

How It Works

EIP-4844 defines a new blob-carrying transaction type. Each block targets 3 blobs and allows a maximum of 6, with each blob holding roughly 0.125 MB of data.

Target blobs per block = 3   (~0.375 MB)
Max blobs per block    = 6   (~0.75 MB)
Blob lifetime          = 4096 epochs (~18 days), then pruned
Pricing: separate blob gas fee market, exponential in blob demand

Blobs have their own base fee, separate from EIP-1559 gas. That blob base fee rises exponentially as blob usage climbs above target and falls when it drops below, similar in spirit to the regular base fee adjustment. The actual blob contents are not stored on-chain in the long run. Instead, Ethereum keeps a small cryptographic commitment, a KZG commitment, that lets parties prove specific data matches the blob without storing all of it permanently. This is the stepping stone to full danksharding, which aims to expand blob capacity much further with data availability sampling.

Worked Example

Consider a rollup that needs to publish a day of transaction data. Before EIP-4844, it bought permanent calldata and competed with every other Ethereum user for gas, so its data bill was large and volatile. That cost was the biggest part of the fee each user paid.

After EIP-4844, the rollup posts the same data in blobs through the separate blob fee market. As long as total blob demand stays near the 3-per-block target, the blob base fee stays low, and the rollup's data bill drops sharply. The rollup passes much of that saving to users, which is why Layer 2 fees fell after the March 2024 upgrade. If many rollups post heavily at once and blob usage pushes toward the 6-per-block cap, the blob base fee climbs and fees rise again until demand eases.

Common Mistakes

1. Expecting blobs to be permanent storage. Blob data is pruned after about 18 days. It is designed for temporary availability, not as a long-term archive on Ethereum.

2. Confusing blob gas with regular gas. Blobs have their own separate fee market. A spike in normal Ethereum gas does not automatically mean blob fees are high, and the reverse is true too.

3. Assuming blob space is unlimited. Each block targets 3 blobs and caps at 6. When many rollups post at once, blob fees can rise just like any congested market.

4. Thinking EIP-4844 is full sharding. Proto-danksharding is a first step. Full danksharding, with much larger capacity and data availability sampling, is a later upgrade.

5. Overlooking the link to Layer 2 fees. Blob costs feed directly into what you pay on a rollup. When blob demand surges, expect Layer 2 fees to follow.

Frequently Asked Questions

What are EIP-4844 blob transactions in simple terms? They are a cheap way for rollups to post their data to Ethereum using temporary data packets called blobs. The blobs are deleted after about 18 days, which keeps the cost low.

How do EIP-4844 blob transactions affect investment decisions? By lowering rollup data costs, they reduce Layer 2 fees and improve the economics of building and using rollups. That can make Layer 2 activity more attractive, though blob demand can still push fees up.

What is a real-world example of EIP-4844 blob transactions? After the March 2024 Dencun upgrade, rollups began posting data in blobs instead of permanent calldata. With blob usage near the target of 3 per block, data costs and Layer 2 fees fell noticeably.

How can investors think about blob fees effectively? Watch blob demand relative to the 3-blob target and 6-blob cap, since fees rise exponentially as usage climbs. A practical rule is that periods of heavy rollup activity can lift Layer 2 fees even with blobs.

How are blob transactions different from EIP-1559 gas? EIP-1559 governs regular transaction gas, with a burned base fee and a tip. Blobs use a separate fee market for rollup data and are stored only temporarily, so the two prices move independently.

Sources

1. Ethereum.org. "Danksharding and Proto-Danksharding (EIP-4844)." https://ethereum.org/en/roadmap/danksharding/
2. Ethereum Improvement Proposals. "EIP-4844: Shard Blob Transactions." https://eips.ethereum.org/EIPS/eip-4844
3. Ethereum.org. "Optimistic Rollups." https://ethereum.org/en/developers/docs/scaling/optimistic-rollups/
4. Ethereum.org. "Layer 2." https://ethereum.org/en/layer-2/

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.