Uniswap Developers

Integrate Flashblocks on Unichain to use preconfirmation data and reduce transaction confirmation latency.

Flashblocks provide transaction preconfirmations on Unichain in about 200 milliseconds, so apps can show faster transaction feedback.

What Are Flashblocks?

Flashblocks enable ultra-fast transaction confirmations on Unichain by providing preconfirmations - instant signals that arrive before the next block is finalized. Instead of waiting up to 1 second for block confirmation, users receive transaction feedback in just 200 milliseconds.

Key benefits

5x faster confirmations: Reduce perceived latency from 1 second to 200 milliseconds
Seamless Integration: Works with many existing Ethereum JSON-RPC methods using the pending tag
No Protocol Changes: Built as an "out-of-protocol" extension that doesn't modify Unichain's core consensus
Incremental Updates: Receive partial block updates as transactions are processed
Backward Compatible: Existing applications continue to work without modifications

How it works

Flashblocks work by streaming partial block updates called "Flashblocks" every 200 milliseconds. Each Flashblock contains:

Transaction Batches: Groups of transactions processed together
State Updates: Account balances, nonces, and storage changes
Execution Results: Transaction receipts and status information

These updates are propagated to RPC providers who maintain a preconfirmation cache, allowing applications to query the latest state immediately.

Perfect for

DeFi Applications: Instant swap confirmations and liquidity updates
Marketplaces: Immediate purchase confirmations
Payment Systems: Instant payment verification
Apps: Deliver more responsive UX without typical blockchain wait times

Integrating Flashblocks (Apps)

Flashblocks integration is designed to be seamless for application developers. Most existing applications can benefit from Flashblocks with minimal code changes.

RPC endpoints

Use these Flashblocks-aware RPC endpoints for development and testing:

Network	URL
Unichain Mainnet	`https://mainnet.unichain.org`
Unichain Sepolia	`https://sepolia.unichain.org`

Production note: These public endpoints are rate-limited. For production applications, see node providers that support Flashblocks.

Supported RPC methods

The following standard Ethereum JSON-RPC methods support Flashblocks data when using the pending tag:

`eth_getBlockByNumber`

Get the latest Flashblock with all preconfirmed transactions:

curl https://sepolia.unichain.org \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getBlockByNumber",
    "params": ["pending", true],
    "id": 1
  }'

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "number": "0x1234",
    "hash": "0x0", // Placeholder during preconfirmation
    "transactions": [...], // All preconfirmed transactions
    "stateRoot": "0x...",
    "gasUsed": "0x...",
    "timestamp": "0x..."
  }
}

`eth_call`

Use the preconfirmation cache state to return the call result:

curl https://sepolia.unichain.org \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_call",
    "params": [{"to": "0x...", "data": "0x..."}, "pending"],  // Transaction call object and block parameter
    "id": 1
  }'

`eth_getTransactionReceipt`

Get receipts for preconfirmed transactions immediately. Notice, no pending tag is needed:

curl https://sepolia.unichain.org \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getTransactionReceipt",
    "params": ["0x..."],
    "id": 1
  }'

`eth_getBalance`

Get the latest balance including preconfirmed transactions:

curl https://sepolia.unichain.org \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getBalance",
    "params": ["0x742d35Cc6634C0532925a3b8D23bb7e67E1b6e0", "pending"],
    "id": 1
  }'

`eth_getTransactionCount`

Get the latest nonce for sending transactions:

curl https://sepolia.unichain.org \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getTransactionCount",
    "params": ["0x742d35Cc6634C0532925a3b8D23bb7e67E1b6e0", "pending"],
    "id": 1
  }'

Library integration

Ethers.js

import { ethers } from 'ethers';

const provider = new ethers.JsonRpcProvider(
  "https://sepolia.unichain.org"
);

const wallet = new ethers.Wallet(process.env.PRIVATE_KEY, provider);

async function sendFastTransaction() {
  const tx = {
    to: "0x742d35Cc6634C0532925a3b8D23bb7e67E1b6e0",
    value: ethers.parseEther("0.001"),
  };

  const submissionTime = Date.now();
  const transaction = await wallet.sendTransaction(tx);

  console.log(`Transaction hash: ${transaction.hash}`);

  // Wait for preconfirmation (0 confirmations)
  await transaction.wait(0);

  const confirmTime = Date.now();
  console.log(`Preconfirmed in ${confirmTime - submissionTime}ms`);
}

Viem

import { createWalletClient, createPublicClient, http, parseEther } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { unichain } from 'viem/chains';

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

const walletClient = createWalletClient({
  account,
  chain: unichain,
  transport: http('https://sepolia.unichain.org'),
});

const publicClient = createPublicClient({
  chain: unichain,
  transport: http('https://sepolia.unichain.org'),
});

async function sendFastTransaction() {
  const submissionTime = Date.now();

  const hash = await walletClient.sendTransaction({
    to: '0x742d35Cc6634C0532925a3b8D23bb7e67E1b6e0',
    value: parseEther('0.001'),
  });

  // Wait for preconfirmation
  const receipt = await publicClient.waitForTransactionReceipt({ hash });

  const confirmTime = Date.now();
  console.log(`Preconfirmed in ${confirmTime - submissionTime}ms`);
}

Integrating Flashblocks (Wallet Providers)

Wallet providers can integrate Flashblocks to provide instant transaction feedback to users.

User experience benefits

Instant Confirmations: Show users their transaction succeeded immediately
Real-time Balance Updates: Update balances as soon as transactions are preconfirmed
Reduced Anxiety: Users don't wait wondering if their transaction went through
Better UX: Feels like Web2 application responsiveness

Implementation guidelines

Transaction status updates

class WalletProvider {
  async sendTransaction(tx) {
    const hash = await this.submitTransaction(tx);

    // Show immediate pending status
    this.updateTransactionStatus(hash, 'pending');

    // Wait for preconfirmation
    try {
      const receipt = await this.waitForPreconfirmation(hash);
      this.updateTransactionStatus(hash, 'preconfirmed');

      // Optional: Wait for full confirmation
      await this.waitForFullConfirmation(hash);
      this.updateTransactionStatus(hash, 'confirmed');
    } catch (error) {
      this.updateTransactionStatus(hash, 'failed');
    }
  }

  async waitForPreconfirmation(hash) {
    return new Promise((resolve, reject) => {
      const checkReceipt = async () => {
        try {
          const receipt = await this.provider.getTransactionReceipt(hash);
          if (receipt) {
            resolve(receipt);
          } else {
            setTimeout(checkReceipt, 100); // Check every 100ms
          }
        } catch (error) {
          reject(error);
        }
      };
      checkReceipt();
    });
  }
}

Balance updates

class WalletProvider {
  async getBalance(address) {
    // Get preconfirmed balance
    const balance = await this.provider.getBalance(address, 'pending');
    return balance;
  }

  async subscribeToBalanceUpdates(address, callback) {
    // Poll for balance changes (or use WebSocket)
    setInterval(async () => {
      const newBalance = await this.getBalance(address);
      callback(newBalance);
    }, 200); // Check every 200ms
  }
}

Using Flashblocks with a Node Provider

For production use cases, consider using a node provider that supports Flashblocks on Unichain.

Alchemy: https://www.alchemy.com/docs/reference/unichain-flashblocks-api-quickstart
Quicknode: https://www.quicknode.com/docs/Unichain/flashblocks/overview

Integrating Flashblocks (Node Operators)

Flashblocks are published via a WebSocket API. Any op-reth node can subscribe to the WebSocket stream and serve pending data. Supported RPC Methods.

Run the docker image ghcr.io/base/node-reth:latest with the binary name ./base-node-reth like a typical op-reth node with the additional flag --websocket-url=wss://mainnet-flashblocks.unichain.org/ws (or the Unichain Sepolia URL if you are running a Unichain Sepolia node).

WebSocket API

You can subscribe to Flashblocks data on the following URLs. The content is Brotli-compressed.

Network	URL
Unichain Mainnet	`wss://mainnet-flashblocks.unichain.org/ws`
Unichain Sepolia	`wss://sepolia-flashblocks.unichain.org/ws`

Example initial response

The initial response contains the base block. Diff responses only contain the transactions that occurred in that flashblock to reduce how much data is sent in each response.

{
  "base": {
    "base_fee_per_gas": "0xa581a9",
    "block_number": "0x1ff5744",
    "extra_data": "0x000000003200000003",
    "fee_recipient": "0x4200000000000000000000000000000000000011",
    "gas_limit": "0x8f0d180",
    "parent_beacon_block_root": "0x6d475c589e1e129ffbdf2518422a4f751221be47b03ee02cc7c0017de7c42cc5",
    "parent_hash": "0x0a6bdd716f4ae846fb0dce22ab2dde4043277c1c69dcb3ce203ae6153ad0d17a",
    "prev_randao": "0xb39a7a9cd133af89a600b98844af7d26b59008b77dadfc7301dcaa470225030c",
    "timestamp": "0x68890b6b"
  },
  "diff": {
    "block_hash": "0xfde1f5d00058b6804aab2298ab8a6137bd736141cc778ed10ee2c2dd92c2e25d",
    "gas_used": "0xb44c",
    "logs_bloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
    "receipts_root": "0x095d9004dd9ac3f1c8a3a09d58a67b8cc6a733a1096a635fa18653564872363f",
    "state_root": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "transactions": [
      "0x7ef90104a04496c450bf25202f5e7ff98ced76e395abe923ec29d8240ea916d47e84db1d6594deaddeaddeaddeaddeaddeaddeaddeaddead00019442000000000000000000000000000000000000158080830f424080b8b0098999be000008dd00101c1200000000000000090000000068890aab00000000015f5ae700000000000000000000000000000000000000000000000000000000760d9ba500000000000000000000000000000000000000000000000000000000000000012d75f34dc6082e101bca0c1084df5e22ef49bde26df171d9e36bfa0fada9f1690000000000000000000000005050f69a9786f081509234f1a7f4684b5e5b76c9000000000000000000000000"
    ],
    "withdrawals": [],
    "withdrawals_root": "0x8bab76e96357f11502327a43179ae1430bf5510aecf9306714359514a1ad5447"
  },
  "index": 0,
  "metadata": {
    "block_number": 33511236,
    "new_account_balances": {
      "0x0000f90827f1c53a10cb7a02335b175320002935": "0x0",
      "0x000f3df6d732807ef1319fb7b8bb8522d0beac02": "0x0",
      "0x4200000000000000000000000000000000000015": "0x0",
      "0xdeaddeaddeaddeaddeaddeaddeaddeaddead0001": "0x69076b18a41d8"
    },
    "receipts": {
      "0x24e20e8a269a497255d19694493edb4fabf239d0d951db06056fc02f62fb3200": {
        "Deposit": {
          "cumulativeGasUsed": "0xb44c",
          "depositNonce": "0x1ff5746",
          "depositReceiptVersion": "0x1",
          "logs": [],
          "status": "0x1"
        }
      }
    }
  },
  "payload_id": "0x032d2c3f8a9826a0"
}

Example diff response

{
  "diff": {
    "block_hash": "0xd7cad1e127fc967c9454d56aa7d97e862ccb7eff83405d79e2be371cb1b6e9d8",
    "gas_used": "0x9d04ea",
    "logs_bloom": "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",
    "receipts_root": "0xa6b611e8baa1097b5689d9cd106b8288aadde4b24fd4e818346c57199e5b05ac",
    "state_root": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "transactions": [
      "0x02f8b282210581fe849502f90084965ac7f682b11c9485e90a5430af45776548adb82ee4cd9e33b0807780b844095ea7b3000000000000000000000000c9740f40d201a349959263acdbd4fbff6dd0e53700000000000000000000000000000000000000000000021e19e0c9bab2400000c001a0dc2a0b293fd334cb393a3471ccd98e92d00e1602202bea1a2b066549c362cf90a0449017bb7f9170936e62451d8db932b7b22a1531c9867cf4530bae965f0ca0ce",
      "0x02f904d5822105820b63840998aa40840ae6c24c830322f69426759dbb201afba361bec78e097aa3942b0b4ab880b90464b4206dd2000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000003e00000000000000000c2db89b2bd434ceac6c74fbc0b2ad3a280e66db01ecf4a5700000000000000000000000000000000000000000000000000000000000001600000000000000000000000000000000000000000000000000000000000000280000000000000000000000000000000000000000000000000000000000000030000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000005f9d660fb31380000000000000000000000000000000000000000000000000000000068890b8300000000000000000000000000000000000000000000000000000000000004b00000000000000000000000000000000000000000000000000000000000001398000000000000000000000000000000000000000000000000000000000000298800000000000000000000000000000000000000000000000000000000003567e034a5c9394fb2fd3298ece07c16ec2ed009f6029a360f90f4e93933b55e2184d40000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000a000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000203b9cf0f6c26f3f86d4bed347520ceabc29872df03a96580be6b1ca67d27d115f000000000000000000000000000000000000000000000000000000000000005268747470733a2f2f647765622e6c696e6b2f697066732f6261666b726569636d776b33786c78626f7a627035683633787979776f636337646c7474333736686e346d6e6d686b376f6a71646362726b717a6900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000004000000000000000000000000000000000000000000000000000000000000000230181a5737464696edc00100000ccd01d00000000ccc0ccb2ccadcca5ccd574cc89ccd100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000041161ac94b4ec55455abd60a0ce4dc64c6ac84e5d34083a803bd6437b3957f9b2f55d975ae81496d5271cb4e69085eddf638ed6def5b0f64c1476692d15204d9c51c00000000000000000000000000000000000000000000000000000000000000c001a0ec961c159e336dc12854bd277c78ea2456baa4059032b431095ed45176202684a04dee750b6435b09d2c8acc52ea3920c309bbe92a210637ccee0fc802937fac7a",
      // more raw transactions
    ],
    "withdrawals": [],
    "withdrawals_root": "0x8bab76e96357f11502327a43179ae1430bf5510aecf9306714359514a1ad5447"
  },
  "index": 1,
  "metadata": {
    "block_number": 33511236,
    "new_account_balances": {
      "0x000000000022d473030f116ddee9f6b43ac78ba3": "0x0",
      "0x0000000071727de22e5e9d8baf0edac6f37da032": "0x2fa696d47dd7f3320",
      // More new balances
    },
    "receipts": {
      "0x02637c55345acb7539a506ba3ed7b1b9bf34dff25495a7554f5f3b7c3fa82c3a": {
        "Eip1559": {
          "cumulativeGasUsed": "0x6e0c96",
          "logs": [],
          "status": "0x1"
        }
      },
      "0x059a9da66abd293fadea0fedad5cfa5e02d8ad44d1a36b16df30fe3dd451fdc2": {
        "Eip1559": {
          "cumulativeGasUsed": "0x822a2b",
          "logs": [
            {
              "address": "0x2a6c106ae13b558bb9e2ec64bd2f1f7beff3a5e0",
              "data": "0xaf73855d4174841d51644d202ecd810eb45916837c087656a308aedf04ac7d5c000000000000000000000000ff5d4f2013563d06a6fd4930fd48ee0ff9c5e622",
              "topics": [
                "0x44d83729a43f9c6046446df014d073dd242e0ad672071e9b292f31b669c25b09"
              ]
            },
            {
              "address": "0x9a593475d9c42d63c117bab7337843b3c0017b3d",
              "data": "0x0000000000000000000000000000000000000000000000000000000000000060000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000c00000000000000000000000000000000000000000000000000000000000000024ee8ca3b5af73855d4174841d51644d202ecd810eb45916837c087656a308aedf04ac7d5c000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
              "topics": [
                "0x8f8f4d49bbb03ffac818a5d588ec1786a4d2d17269871cbf5b1745f58b64c15d",
                "0x0000000000000000000000002a6c106ae13b558bb9e2ec64bd2f1f7beff3a5e0"
              ]
            },
            {
              "address": "0x2a6c106ae13b558bb9e2ec64bd2f1f7beff3a5e0",
              "data": "0xaf73855d4174841d51644d202ecd810eb45916837c087656a308aedf04ac7d5c000000000000000000000000ff5d4f2013563d06a6fd4930fd48ee0ff9c5e622",
              "topics": [
                "0x44d83729a43f9c6046446df014d073dd242e0ad672071e9b292f31b669c25b09"
              ]
            },
            {
              "address": "0x2a6c106ae13b558bb9e2ec64bd2f1f7beff3a5e0",
              "data": "0xaf73855d4174841d51644d202ecd810eb45916837c087656a308aedf04ac7d5c78b4356abb078cdc094ed57916001faac8620301a832170438f98917d256b2c80000000000000000000000000000000000000000000000000000000000000001",
              "topics": [
                "0x6bc93adab97dd835bee818087939b726558bc8d9177650a0018dd05eb00e56c8"
              ]
            },
            {
              "address": "0x08efb6d315c7e74c39620c9aaea289730f43a429",
              "data": "0x78b4356abb078cdc094ed57916001faac8620301a832170438f98917d256b2c80000000000000000000000002a6c106ae13b558bb9e2ec64bd2f1f7beff3a5e0000000000000000000000000df8f2aeea963803140df7b4ddd11216e584577b4000000000000000000000000620d7e459cffcdc56a874536dc19147de801a4a1",
              "topics": [
                "0xc6cfec28363edf86fe132edcedb30ccc6dbb89a7ec5f428aaeeb8ae5d901537d"
              ]
            }
          ],
          "status": "0x1"
        }
      },
      // More receipts
  },
  "payload_id": "0x032d2c3f8a9826a0"
}

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Integrating Flashblocks

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