Optimism Documentation

Flashblocks-enabled chains stream pre-confirmations every few hundred milliseconds, so your app can show transaction results well before the next full block is sealed. This guide shows how to read that pre-confirmed state over standard Ethereum JSON-RPC and from the viem and ethers libraries. For how Flashblocks work under the hood, see the Flashblocks explainer. Integration is designed to be simple and low-friction. Most apps benefit with minimal code changes.

In production, point your app to a Flashblocks‑aware RPC endpoint from your provider of choice. If your provider doesn’t support flashblocks yet, let us know on Discord and we’ll work with them to get it added.
Alternatively, you can run your own flashblocks-aware node using Base’s reth image.

Supported RPC methods

Developers can access Flashblocks using the same familiar Ethereum JSON-RPC calls. The difference is using the “pending” tag in some of them to explicitly query the pre-confirmed state instead of the last finalized block.

eth_getBlockByNumber: Use the pending tag to retrieve the latest flashblock snapshot.

Show Sample response

    {
      "jsonrpc": "2.0",
      "id": 1,
      "result": {
        "number": "0x1234",
        "hash": "0x...",
        "transactions": [...]
      }
    }

eth_call: Use the pending tag to execute calls against the most recent pre-confirmed state.

Show Sample request

{
  "jsonrpc": "2.0",
  "method": "eth_call",
  "params": [{"to": "0x...", "data": "0x..."}, "pending"],
  "id": 1
}

eth_estimateGas: With pending, estimates gas usage against the latest Flashblock

Show Sample request

{
  "jsonrpc": "2.0",
  "method": "eth_estimateGas",
  "params": [{"from":"0x...","to":"0x...","value":"0x..."}, "pending"],
  "id": 1
}

eth_getBalance / eth_getTransactionCount: Use the pending tag to fetch balances or transaction counts respectively as they evolve within the block window.
Show Sample response for `eth_getBalance`
{ "jsonrpc": "2.0", "id": 1, "result": "0x0234" }
Show Sample response for `eth_getTransactionCount`
{ "jsonrpc": "2.0", "id": 1, "result": "0x1b" // 27 transactions }
Other methods, like eth_getTransactionReceipt, eth_getTransactionByHash or eth_simulateV1, return data from pre-confirmed transactions without requiring the pending tag. Consult the Flashblocks specification for more details on each of these methods.

Libraries

You will need a Flashblocks‑aware RPC endpoint to use the following libraries:

Viem

import { createPublicClient, createWalletClient, http, parseEther } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { opSepolia } from 'viem/chains';
import { publicActionsL2, walletActionsL2 } from 'viem/op-stack';

const account = privateKeyToAccount(`0x${process.env.PRIVATE_KEY}`);

const walletClient = createWalletClient({
  account,
  chain: opSepolia,
  transport: http("https://sepolia.optimism.io"),
}).extend(walletActionsL2());

const publicClient = createPublicClient({
  chain: opSepolia,
  transport: http("https://sepolia.optimism.io"),
}).extend(publicActionsL2());

const submissionTime = new Date();
const hash = await walletClient.sendTransaction({
  to: '0x...',
  value: parseEther('0.0001'),
});

// Wait for pre-confirmation
const receipt = await publicClient.waitForTransactionReceipt({ hash });
const confirmTime = new Date();
console.log('pre-confirmed in ms:', confirmTime.getTime() - submissionTime.getTime());

Ethers

import { ethers } from 'ethers';

// Here, provider is a Flashblocks-enabled RPC provider
const provider = new ethers.JsonRpcProvider("https://sepolia.optimism.io");
const wallet = new ethers.Wallet(process.env.PRIVATE_KEY as string, provider);

const tx = { to: '0x...', value: ethers.parseEther('0.0001') };
const submission = new Date();

const sent = await wallet.sendTransaction(tx);

await sent.wait(0);
const confirmed = new Date();

// should represent the transaction (pre)confirmation faster than standard RPC
console.log('Pre-confirmed in ms:', confirmed.getTime() - submission.getTime());

// validates the transaction hash returned by the pre-confirmed transaction above
const receipt = await provider.getTransactionReceipt(sent.hash);
const validated = new Date();
console.log('Receipt validated in ms:', validated.getTime() - submission.getTime());
console.log('Transaction receipt:', receipt);

Next steps

Understand how Flashblocks affect gas usage and large transactions.
Learn how Flashblocks work in the Flashblocks explainer.
Review the technical specs for architecture details.
Join our community to share best practices and get support!

​Supported RPC methods

​Libraries

​Viem

​Ethers

​Next steps

Supported RPC methods

Libraries

Viem

Ethers

Next steps