newFlashblocks

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

string

required

Must be "newFlashblocks".

Returns

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

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

{"jsonrpc": "2.0", "id": 1, "result": "0x3b8cd9e5f4a7b2c1d0e3f4a5b6c7d8e9"}

import WebSocket from 'ws';

// Use a Flashblocks-enabled provider WSS endpoint (see the Base Services Hub)
const ws = new WebSocket('wss://your-flashblocks-provider.example/ws');

ws.on('open', () => {
  ws.send(JSON.stringify({
    jsonrpc: '2.0',
    method: 'eth_subscribe',
    params: ['newFlashblocks'],
    id: 1
  }));
});

ws.on('message', (data) => {
  const msg = JSON.parse(data.toString());
  if (msg.method === 'eth_subscription') {
    // Fires every ~200ms with the latest Flashblock state
    console.log('Flashblock update:', msg.params.result);
  }
});

Overview

CLIs

Base Chain API

Base Verify API

Migrated Documentation

Parameters

Returns

Example

​Parameters

​Returns

​Example

Parameters

Returns

Example