Back to: L2 Developer Path
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Objective: understand the data layer that made cheap L2s possible — and its limits.
Before EIP-4844, rollups posted data as expensive L1 calldata. Now they attach blobs: ~128 KB chunks on a separate fee market, pruned after ~18 days. L2 fees fell roughly 10x overnight.
Concept: why temporary data is enough
Fraud and validity verification only need data *while challenges are possible*. After finality, history lives with indexers and explorers — the protocol guarantees availability during the window that matters, not eternal storage. Separate pricing means blob demand doesn’t fight your wallet’s gas price (until blobs themselves congest).
Hands-on lab (free)
- Open any recent Ethereum block on an explorer and find its blob count + blob base fee.
- Compare an Arbitrum swap fee today vs pre-4844 charts (archived analyses).
- Watch blob fees during a busy hour: note how an independent fee market behaves.
Safety checklist
- Blob expiry means *you* archive anything you need permanently (tax records, proofs).
- Blob congestion still prices out small rollups first — diversification across L2s isn’t just tribal.
- Don’t confuse cheap fees with decentralization; the sequencer question is separate.
Related glossary
Next lesson: sequencer risks — the centralization hiding in plain sight.