# OP Mainnet Flashblocks API quickstart

> Get started building on Optimism using Flashblocks

> For the complete documentation index, see [llms.txt](/docs/llms.txt).

## What are Flashblocks?

Flashblocks on Optimism are a transaction preconfirmation feature that provides near-instant transaction feedback by streaming partial block updates every 200 milliseconds. This significantly reduces the effective block time from Optimism's standard 2 seconds to 200 milliseconds, a 10x improvement.

Flashblocks is great for developers who demand instant UX such as decentralized exchanges, onchain gaming, and other high-frequency applications.

## Getting started

Flashblocks is currently supported on both Optimism Sepolia testnet and mainnet and can be accessed using your existing **Alchemy Optimism** RPC.

| Network       | Flashblocks Availability |
|---------------|---------------------------|
| Optimism Sepolia  | ✅                        |
| Optimism Mainnet  | ✅                        |

## Flashblocks-enabled API endpoints

### [eth\_getBlockByNumber](https://www.alchemy.com/docs/node/op-mainnet/op-mainnet-api-endpoints/eth-get-block-by-number)

Use the `pending` tag to retrieve the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["pending",true],"id":1}'
```

#### Example Response

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

### [eth\_getTransactionReceipt](https://www.alchemy.com/docs/node/op-mainnet/op-mainnet-api-endpoints/eth-get-transaction-receipt)

Use the existing receipt RPC to get preconfirmed receipts:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getTransactionReceipt","params":["0x..."],"id":1}'
```

#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "transactionHash": "0x...",
    "blockNumber": "0x1234",
    "status": "0x1"
  }
}
```

### [eth\_getBalance](https://www.alchemy.com/docs/node/op-mainnet/op-mainnet-api-endpoints/eth-get-balance)

Use the `pending` tag to get the address balance in the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x...","pending"],"id":1}'
```

#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x0234"
}
```

### [eth\_getTransactionCount](https://www.alchemy.com/docs/node/op-mainnet/op-mainnet-api-endpoints/eth-get-transaction-count)

Use the `pending` tag to get the address nonce in the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getTransactionCount","params":["0x...","pending"],"id":1}'
```
#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x1b" // 27 transactions
}
```

### [eth\_getTransactionByHash](https://www.alchemy.com/docs/node/op-mainnet/op-mainnet-api-endpoints/eth-get-transaction-by-hash)

Use the existing get transaction by hash RPC to get preconfirmed transactions:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getTransactionByHash","params":["0x..."],"id":1}'
```

#### Example Response

```bash
{
  "type": "0x2",
  "chainId": "...",
  "nonce": "...",
  ...
}
```

### [eth\_call](https://www.alchemy.com/docs/chains/op-mainnet/op-mainnet-api-endpoints/eth-call)

Use the `pending` tag to execute a smart contract call against the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_call","params":[{"to":"0x...","data":"0x..."},"pending"],"id":1}'
```

#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x0000000000000000000000000000000000000000000000000000000000000001"
}
```

### [eth\_simulateV1](https://www.alchemy.com/docs/chains/op-mainnet/op-mainnet-api-endpoints/eth-simulate-v-1)

Use the `pending` tag to simulate transactions against the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_simulateV1","params":[{"blockStateCalls":[{"calls":[{"to":"0x...","data":"0x..."}],"stateOverrides":{}}],"traceTransfers":true,"validation":true},"pending"],"id":1}'
```

#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": [
    {
      "calls": [
        {
          "status": "0x1",
          "gasUsed": "0x5208",
          "returnData": "0x"
        }
      ]
    }
  ]
}
```

### [eth\_estimateGas](https://www.alchemy.com/docs/chains/op-mainnet/op-mainnet-api-endpoints/eth-estimate-gas)

Use the `pending` tag to estimate gas against the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_estimateGas","params":[{"to":"0x...","data":"0x..."},"pending"],"id":1}'
```

#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x5208"
}
```

### [eth\_getLogs](https://www.alchemy.com/docs/chains/op-mainnet/op-mainnet-api-endpoints/eth-get-logs)

Use the `pending` tag for toBlock to retrieve logs from the latest Flashblock:

```bash
curl https://opt-sepolia.g.alchemy.com/v2/<YOUR_API_KEY> -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getLogs","params":[{"fromBlock":"latest","toBlock":"pending","address":"0x...","topics":["0x..."]}],"id":1}'
```

#### Example Response

```bash
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": [
    {
      "address": "0x...",
      "topics": ["0x..."],
      "data": "0x...",
      "blockNumber": "0x1234",
      "transactionHash": "0x...",
      "transactionIndex": "0x0",
      "blockHash": "0x...",
      "logIndex": "0x0",
      "removed": false
    }
  ]
}
```