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Flashblocks

type: conceptconfidence: highupdated: 2026-06-19sources: 2

Flashblocks are 200ms incremental state updates the Base sequencer streams between full blocks, sharply reducing perceived latency — users see their transaction reflected in ~200ms rather than waiting a full ~1s block.

Key facts

Always on. Every Base block is built by the Flashblocks builder; Flashblocks are not optional and are always live.
Preconfirmation, not finality. A Flashblock is an early, partial view of the block being built. It gives fast UX feedback; full settlement still follows the normal block → L1 batch → proof path (chain-architecture, proof-system).
Two ways to consume — a dedicated WebSocket stream of incremental Flashblock updates, and standard RPC methods that surface the latest "pending" Flashblock state (the newflashblocks / pending-logs surfaces in docs-catalog).

Building against it

Apps wanting the snappiest UX subscribe to the Flashblocks WebSocket and optimistically reflect the preconfirmed state, then reconcile against the confirmed block. Latency-sensitive reads can target the pending Flashblock. This 200ms cadence is one of the concrete differences from Ethereum.