Welcome to Across

MegaETH is now live on Across. Bridge to and from MegaETH (Chain ID 4326) using the Swap API.

What is Across?

Across is a crosschain interoperability protocol that provides the fastest, cheapest, and most secure way to move assets across blockchains. With ~2 second fills on mainnet and support for 23+ chains, Across powers crosschain swaps, bridges, and embedded actions through a single unified API.

Unlike single-mechanism bridges, Across intelligently routes through three distinct settlement pathways to optimize for speed, cost, and transfer size.

The Swap API automatically selects the optimal pathway — you don't need to choose.

API key required for production. Request your API key and integrator ID or reach out on Telegram.

Quick Start

Get a crosschain swap executing in three steps:

Get a Quote

Call the Swap API with your transfer parameters to get executable calldata.

get-quote.ts

const params = new URLSearchParams({
  tradeType: "minOutput",
  originChainId: "42161",        // Arbitrum
  destinationChainId: "8453",    // Base
  inputToken: "0xaf88d065e77c8cC2239327C5EDb3A432268e5831",  // USDC on Arbitrum
  outputToken: "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", // USDC on Base
  amount: "1000000000",          // 1000 USDC (6 decimals)
  depositor: "0xYourWalletAddress",
  integratorId: "0xdead",        // Your integrator ID
});

const response = await fetch(
  `https://app.across.to/api/swap/approval?${params}`,
  {
    headers: {
      Authorization: "Bearer YOUR_API_KEY",
    },
  }
);
const quote = await response.json();

Approve Token Spending

If the quote includes approval transactions, execute them first.

approve.ts

import { createWalletClient, http } from "viem";
import { arbitrum } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";

const account = privateKeyToAccount("0xYOUR_PRIVATE_KEY");
const walletClient = createWalletClient({
  account,
  chain: arbitrum,
  transport: http(),
});

if (quote.approvalTxns?.length) {
  for (const approvalTx of quote.approvalTxns) {
    const hash = await walletClient.sendTransaction({
      to: approvalTx.to,
      data: approvalTx.data,
    });
    console.log("Approval tx:", hash);
  }
}

Execute the Swap

Send the main swap transaction using the calldata from the quote.

execute.ts

const hash = await walletClient.sendTransaction({
  to: quote.swapTx.to,
  data: quote.swapTx.data,
  value: quote.swapTx.value ? BigInt(quote.swapTx.value) : 0n,
  gas: quote.swapTx.gas ? BigInt(quote.swapTx.gas) : undefined,
});

console.log("Swap tx:", hash);
// Funds arrive on Base in ~2 seconds

What's Next

Across for Stablecoins

Learn how CCTP and OFT settlement enable native stablecoin transfers at scale.

Swap API

Deep dive into the Swap API — parameters, response structure, and integration patterns.

Working with Hypercore

Bridge assets to Hyperliquid's sub-second settlement layer.