What Are Blobs?
Blobs are large, temporary data packages Ethereum added in the March 2024 Dencun upgrade (EIP-4844, proto-danksharding). Layer 2 rollups post their transaction data in blobs instead of stuffing it into regular calldata. Blob space has its own fee market, usually much cheaper, which is why L2 fees collapsed after the upgrade.
How It Actually Works
- A blob is attached to a block, available long enough for honest parties to retrieve it (weeks, not forever), then pruned from the consensus layer. Archives still keep history; full nodes do not have to.
- That is the data-availability bargain: Ethereum attests "this data was published" without executing every L2 transaction and without storing it for a decade on every laptop node.
- Regular ETH transfers and DeFi calls still pay the old EIP-1559 gas market. Blobs did not make mainnet swaps free.
Risks and Common Mistakes
- Assuming every cheap chain is using blobs. Some "L2s" still hide data off-chain. Check L2Beat.
- Treating a blob-fee spike as an ETH-gas spike, or the reverse. Two markets, two dashboards.
When It Matters
Paying fees on Arbitrum, Base, Optimism, and friends, and reading any "Ethereum scaling" headline after 2024. The user-facing win is cheaper L2s, not a new coin.
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