newFlashblocks

Subscribe to receive full Flashblock payload stream as each pre-confirmed block is built. Only available on Flashblocks WebSocket endpoints.

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.

This subscription requires a WebSocket-enabled RPC endpoint. The public Base endpoints (mainnet.base.org, sepolia.base.org) are HTTP only. Choose a Flashblocks-capable WebSocket provider from the Base Services Hub.

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.

Parameters

subscriptionType · string · required

Must be "newFlashblocks".

Returns

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.

Example

Subscribe

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