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Subscribe via eth_subscribe to receive full block state updates as each Flashblock is built. Each message contains the accumulated pre-confirmed state for the block in progress.
Only available on Flashblocks WebSocket endpoints: wss://mainnet-preconf.base.org and wss://sepolia-preconf.base.org.
Requires base/base minimum client version v0.3.1.
Each subscription emits one Flashblock Object per WebSocket message. Events arrive approximately every 200ms. If your handler performs heavy processing per event, throttle or debounce it to avoid blocking.

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Parameters

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subscriptionType
string
required
Must be "newFlashblocks".

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Returns

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result
string
Hex-encoded subscription ID. Each event notification delivers a Flashblock Object — not a standard block object. The payload contains payload_id, index, diff, and (on index 0) base. See the Infrastructure Stream schema for the full structure.

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Example

{"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["newFlashblocks"]}