# Ethereum blobs and data availability Blobs are a way to publish data alongside Ethereum transactions, designed for uses such as rollups. Their data is handled separately from EVM execution and has a separate fee market. Availability lets others obtain and check the data; it is not a promise of permanent storage. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md); [Data availability](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/data-availability/index.md); [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md) Canonical: https://degreesofsatoshi.com/encyclopedia/ethereum-blobs-data-availability/ Published: 2026-10-02 Substantively modified: 2026-10-02 Independently verified by an automated reviewer: 2026-10-02T15:10:23.134Z AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied. ## Key facts - **Purpose:** Publish data needed by systems such as rollups ([EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md); [Data availability](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/data-availability/index.md)) - **Execution:** EVM execution can reference blob commitments but cannot read arbitrary blob contents directly ([EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md)) - **Cost:** Blob gas has a fee market distinct from execution gas ([EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md)) ## Other people need the inputs, not just a claimed result A rollup can announce a new state commitment, but a commitment is only a compact reference to data. Independent participants need the relevant data to reconstruct balances and execution, challenge incorrect results where applicable, and prepare operations such as withdrawals. Data availability asks whether that data can be obtained when the network accepts the result. It differs from execution validity, which asks whether the state transition follows the rules. A system needs an explanation for both questions. Evidence: [Data availability](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/data-availability/index.md); [Optimistic rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/optimistic-rollups/index.md); [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md) ## Blob data travels beside execution EIP-4844 introduced a transaction type that refers to blobs through cryptographic commitments. The execution layer processes the transaction while the blob data is handled separately. The EVM has access to a versioned hash reference, not an instruction that reads arbitrary bytes from the blob. This separation lets Ethereum price and handle data publication differently from ordinary execution. A rollup can use that publication channel while its own software interprets the data. A blob is not a smart contract, a new account or a general promise to host a file forever. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md) ## Example: sharing a publication cost across a batch Suppose a hypothetical rollup spends 0.001 ETH publishing data for a batch containing 100 equally sized actions. Dividing that one cost equally gives 0.00001 ETH per action. This illustrates how batching can spread a shared publication expense. It is not a fee quote. Real batches contain different data sizes, compression varies, blob demand changes, and users also pay for execution and other protocol costs. A rollup’s pricing policy decides how those expenses appear in the user’s final fee. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md); [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md) ## Availability and long-term retrieval are different services The protocol has a bounded obligation to serve blob data rather than a promise that every node retains it permanently. Historical reconstruction beyond that availability window requires retained copies or archival services. A hash proves which data was committed; it cannot regenerate missing bytes. Blob capacity, pricing parameters and distribution mechanisms can change with network upgrades. This entry describes the mechanism and deliberately does not present the original EIP’s capacity constants as current limits. For a live operational limit, identify the active fork and client specification. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md); [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md); [Data availability](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/data-availability/index.md) ## Questions ### Can a smart contract read all the bytes in a blob? Not directly through normal EVM execution. EIP-4844 exposes references and a verification mechanism, while blob contents are handled outside the execution data available to contracts. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md) ### Does availability mean the data is stored forever? No. Availability at acceptance and permanent archival retrieval are separate guarantees. Older blob data requires retained copies. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md); [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md) ### Do blobs make every rollup transaction cheap? No. They provide a separate data publication channel. Demand, batch usage, execution costs and the rollup’s fee policy still affect what a user pays. Evidence: [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md); [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md) ## Claims and scope ### ethereum-blobs-data-availability-quick-answer Blobs are a way to publish data alongside Ethereum transactions, designed for uses such as rollups. Their data is handled separately from EVM execution and has a separate fee market. Availability lets others obtain and check the data; it is not a promise of permanent storage. Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ### ethereum-blobs-data-availability-fact-purpose Purpose: Publish data needed by systems such as rollups Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ### ethereum-blobs-data-availability-fact-execution Execution: EVM execution can reference blob commitments but cannot read arbitrary blob contents directly Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ### ethereum-blobs-data-availability-fact-cost Cost: Blob gas has a fee market distinct from execution gas Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ## Sources - [EIP-4844: Shard Blob Transactions](https://raw.githubusercontent.com/ethereum/EIPs/ac912ca6a9685590345dd8e5736cda75976d0131/EIPS/eip-4844.md) — Ethereum Improvement Proposals. Defines blob commitments, separately priced blob gas and time-limited data serving; original capacity constants are not treated as current limits. Locator: Abstract; gas accounting; consensus-layer validation; rationale. Retrieved: 2026-10-02T14:35:51.590523+00:00. - [Data availability](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/data-availability/index.md) — ethereum.org contributors. Supports why a hash is not sufficient to reconstruct data and why availability differs from permanent historical storage. Locator: Data availability problem; rollups; availability versus retrievability. Retrieved: 2026-10-02T14:35:47.112785+00:00. - [Zero-knowledge rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/zk-rollups/index.md) — ethereum.org contributors. Supports validity proofs and public rollup data; no claim that every withdrawal is instant or that every ZK system is private. Locator: Data availability; validity proofs; withdrawals; EVM compatibility. Retrieved: 2026-10-02T14:35:47.579728+00:00. - [Optimistic rollups](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/scaling/optimistic-rollups/index.md) — ethereum.org contributors. Supports challenge periods, dispute verification, sequencer ordering and withdrawal distinctions; concrete timings depend on the implementation. Locator: Fraud proving; censorship resistance; exiting the rollup. Retrieved: 2026-10-02T14:35:47.579696+00:00. ## Revision history - 2026-10-02: First publication after primary-source research and independent automated verification. ## Cite this entry Degrees of Satoshi editorial project. “Ethereum blobs and data availability.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/ethereum-blobs-data-availability/