Crypto Gloss

Blob Transactions

Blob transactions are an Ethereum transaction type introduced by EIP-4844 as part of the Dencun hard fork (March 2024), designed specifically to reduce the cost of posting data from L2 rollups to Ethereum L1. Before EIP-4844, rollups (Optimism, Arbitrum, Base, etc.) posted compressed transaction batches as calldata to Ethereum smart contracts — expensive because calldata is processed by every full node, stored permanently in blockchain history, and priced accordingly. EIP-4844 introduces a separate blob data type: binary data up to 128KB in size, attached to a transaction but stored separately from the main Ethereum state, available for ~18 days (4,096 epochs), then pruned. Blobs have their own fee market (blob gas, independent of regular gas), and because they’re temporary and not processed by the EVM, they’re dramatically cheaper than calldata — reducing L2 data posting costs by 10–100x in practice.

How It Works

The following sections cover this in detail.

Blob Structure

A blob is:

  • A binary data object of exactly 4,096 field elements × 32 bytes = 128KB
  • Each blob is accompanied by a KZG commitment (blob_kzg_commitment) — a cryptographic commitment binding the block proposer to the blob’s contents
  • And a KZG proof verifying that the commitment is correct

The actual blob data is propagated on the consensus layer p2p network (not the execution layer), stored by beacon nodes for the pruning window (~18 days / 4,096 epochs), and then deleted. Full nodes only need to verify KZG commitments — not the full blob data — for long-term chain validity.

Why This Is Cheap

Calldata (the old approach):

  • Every byte is part of Ethereum’s permanent transaction record
  • Every full node processes and stores it forever
  • Priced at ~16 gas/byte (4 gas for zero bytes) — expensive for large data

Blob data:

  • Not part of the EVM state — never processed by the EVM
  • Pruned after ~18 days — not stored permanently by full nodes
  • Independent fee market: blob gas (separate from regular gas base fee), with its own EIP-1559 adjustment
  • Target: 3 blobs per block (Dencun) → 6 blobs per block (Pectra)

When L2 activity is low (blob demand < target), blob base fee is nearly zero. When high, it adjusts upward. L2 fees track blob gas prices directly.

KZG Commitments

Each blob is committed using KZG polynomial commitments — the same cryptography planned for Verkle trees. A KZG commitment C to a blob B proves that B‘s data is what it says it is without requiring full data broadcast to everyone:

  • Light nodes can verify a blob’s commitment without downloading the full 128KB
  • This enables Data Availability Sampling (DAS) — the key to full danksharding in the future

The KZG trusted setup: EIP-4844 required a one-time “Powers of Tau” KZG ceremony. 140,000+ participants contributed — making the chance of the ceremony’s “toxic waste” being reconstructed computationally negligible.

Impact on L2 Fees

The effect of EIP-4844 on L2 fees was immediate and dramatic:

L2 Pre-Dencun avg tx fee Post-Dencun avg tx fee
Optimism ~$0.50–$2.00 ~$0.01–$0.05
Arbitrum ~$0.10–$0.50 ~$0.01–$0.03
Base ~$0.15–$1.00 ~$0.005–$0.02
zkSync ~$0.20–$1.50 ~$0.005–$0.02

Fees dropped 90%+ for most L2s — aligning with Ethereum’s “rollup-centric roadmap” vision of L2s for cheap user transactions settled securely on L1.

Blob Throughput Expansion

EIP-4844 set a target of 3 blobs/block (max 6). The Pectra hard fork (EIP-7691) raised this to target 6 blobs/block (max 9), doubling throughput capacity for L2 data posting.

Full danksharding (the long-term goal) would scale blob throughput to 64–128 blobs per block, enabling Data Availability Sampling where light nodes verify data availability without downloading full blobs — enabling massive L2 scalability without increasing full node hardware requirements.

History

  • 2022 — EIP-4844 proposed by Vitalik Buterin, Dankrad Feist, Diederik Loerakker, Preston Van Loon, and others as “Proto-Danksharding” — a step toward full danksharding.
  • 2022–2023 — KZG trusted setup ceremony runs: 140,000+ participants contribute on kzg-ceremony.ethereum.org.
  • 2023 — Goerli/Sepolia/Holesky testnet activations of EIP-4844 with blob transactions.
  • 2024, March 13 — Dencun hard fork activates on mainnet, including EIP-4844. L2 fees drop 90%+ within hours.
  • 2024–2025 — Blob demand grows as L2 activity increases; blob base fee rises during high-traffic periods.
  • 2025 — Pectra hard fork (EIP-7691) doubles blob target to 6/block, increasing L2 bandwidth further.
  • Roadmap: full danksharding — Future upgrade targeting 64+ blobs/block with DAS, enabling L2s to scale to global transaction throughput.

Common Misconceptions

“Blob data is stored on Ethereum forever.”

Blobs are explicitly temporary — pruned after ~18 days. This is intentional and by design. Rollups that need permanent data availability for fraud proofs or ZK proofs post data commitments (hashes) on-chain permanently; the full blob data is separately archived by rollup operators and third-party archivers (like the EthStorage network).

“Blobs are free.”

Blobs have their own fee market with a base fee (blob gas), which follows EIP-1559 dynamics. During high demand periods (L2 congestion), blob fees rise. Most of the time blob fees are very low; during peak usage, costs for L2 operators increase.

“EIP-4844 is the same as EIP-4844 (danksharding).”

EIP-4844 is proto-danksharding — an intermediate step that introduces the blob type and KZG commitments but doesn’t implement full danksharding (which requires DAS for light client verification). Danksharding is a future upgrade.

Criticisms

  1. Blob data is temporary — Rollup operators must independently archive blob data beyond the 18-day window; there’s no protocol-level guarantee of long-term data availability. This introduces a weak link for very long fraud proof windows (optimistic rollups originally had 7-day challenge periods; some moved to 1-day in response).
  2. Blob target may need frequent increases — L2 growth outpacing blob target capacity creates recurring congestion; EIP-7691 in Pectra doubles the target, but full danksharding is still far off.
  3. Centralization of blobs on full nodes — During the ~18-day window, only beacon nodes that store blobs provide the data. If beacon node operators heavily prune immediately, data may become unavailable before the official window closes — light client data availability assumptions become weaker.

Social Media Sentiment

The Dencun hard fork (which activated EIP-4844) was one of the most celebrated Ethereum events of 2024 on Twitter/X — L2 teams (Base official account, Arbitrum, Optimism) all posted fee comparison screenshots celebrating the drops. r/ethereum and r/ethfinance had extensive post-Dencun threads with real-time fee tracking. The KZG ceremony was unique in generating public participation across crypto Twitter — many accounts posted their ceremony contribution hashes. Critics of Ethereum’s scalability acknowledged EIP-4844 as a real improvement, though some positioned it as “should have happened 3 years ago.”

Last updated: 2026-04

Related Terms

Sources

  1. Buterin, V. et al. (2022). EIP-4844: Shard Blob Transactions. Ethereum Improvement Proposals, GitHub.
  1. Feist, D. (2022). Proto-Danksharding FAQ. notes.ethereum.org.
  1. Ethereum Foundation (2024). Dencun Mainnet Upgrade: EIP-4844 Activation. blog.ethereum.org.
  1. Thibault, L.T. et al. (2022). “Blockchain Scaling Using Rollups: A Comprehensive Survey.” IEEE Access, 10, 93039–93059.