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Relay supports deposits to and withdrawals from Bitcoin across any supported chain. This guide covers the Bitcoin-specific parameters, PSBT signing, balance calculation, and API/SDK usage required for integration.

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Required Information

Bitcoin transactions differ from EVM chains in several ways. The sections below highlight the Bitcoin-specific parameters and requirements for your integration.
Bitcoin addresses are case-sensitive.

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SDK Properties

ActionParameterInputDescription
Deposit to BitcointoChainId8253038Chain ID assigned to Bitcoin in Relay.
recipientUser’s Bitcoin AddressValid Bitcoin address.
toCurrencybc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8Native BTC identifier.
Withdraw from BitcoinchainId8253038Chain ID assigned to Bitcoin in Relay.
currencybc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8Native BTC identifier.

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Bitcoin Currency

TokenCurrency AddressSymbolDecimals
BTCbc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8BTC8

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PSBT Signing

Bitcoin transactions use Partially Signed Bitcoin Transactions (PSBT) for signing. When withdrawing from Bitcoin, the quote response returns a PSBT instead of standard EVM calldata. The Bitcoin wallet adapter handles PSBT parsing, finalization, and broadcasting. Provide a signPsbt callback that signs the PSBT and returns the signed result in base64 format.

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UTXOs and Bitcoin Balance

Unlike EVM chains that track account balances directly, Bitcoin uses a UTXO (Unspent Transaction Output) model. Each address balance equals the sum of unspent outputs it has received minus outputs it has spent. To calculate a Bitcoin address balance, query the mempool.space API and compute the difference between funded and spent transaction outputs: 
async function getBitcoinBalance(address: string) {
	const response = await fetch(
		`https://mempool.space/api/address/${address}`
	);
	const data = await response.json();

	const fundedTxo = data.chain_stats.funded_txo_sum;
	const spentTxo = data.chain_stats.spent_txo_sum;
	const pendingSpent = data.mempool_stats.spent_txo_sum;

	// Balance in satoshis
	const balance =
		BigInt(fundedTxo) - BigInt(spentTxo) - BigInt(pendingSpent);

	return {
		balance, // Confirmed balance in satoshis
		pendingBalance: BigInt(pendingSpent), // Pending outgoing
	};
}
Balance values are returned in satoshis (1 BTC = 100,000,000 satoshis).

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API

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Params

ActionParameterInputDescription
Deposit to BitcoinrecipientUser’s Bitcoin AddressValid Bitcoin address.
destinationChainId8253038Chain ID assigned to Bitcoin in Relay.
destinationCurrencybc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8Native BTC identifier.
Withdraw from BitcoinuserUser’s Bitcoin AddressValid Bitcoin address.
originChainId8253038Chain ID assigned to Bitcoin in Relay.
originCurrencybc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8Native BTC identifier.

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Execution

Bitcoin uses the standard Relay API flow. Review the execution steps documentation, then use the Get Quote endpoint.

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Example: Withdraw from Bitcoin to Base

curl -X POST "https://api.relay.link/quote/v2" \
  -H "Content-Type: application/json" \
  -d '{
    "user": "bc1q4vxn43l44h30nkluqfxd9eckf45vr2awz38lwa",
    "originChainId": 8253038,
    "originCurrency": "bc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8",
    "destinationChainId": 8453,
    "destinationCurrency": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913",
    "recipient": "0x03508bb71268bba25ecacc8f620e01866650532c",
    "tradeType": "EXACT_INPUT",
    "amount": "100000"
  }'

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Example: Deposit to Bitcoin from Base

curl -X POST "https://api.relay.link/quote/v2" \
  -H "Content-Type: application/json" \
  -d '{
    "user": "0x03508bb71268bba25ecacc8f620e01866650532c",
    "originChainId": 8453,
    "originCurrency": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913",
    "destinationChainId": 8253038,
    "destinationCurrency": "bc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8",
    "recipient": "bc1q4vxn43l44h30nkluqfxd9eckf45vr2awz38lwa",
    "tradeType": "EXACT_INPUT",
    "amount": "10000000"
  }'
Amounts are specified in the smallest unit of the currency. For BTC, this is satoshis (100000 satoshis = 0.001 BTC). For USDC, this is 6 decimal places (10000000 = 10 USDC).

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SDK

To use the SDK with Bitcoin, install and configure the Bitcoin wallet adapter. The adapter handles PSBT signing and transaction broadcasting. 
npm install @relayprotocol/relay-bitcoin-wallet-adapter
For implementation details and code samples, see the Adapters documentation.

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Deposit Addresses (Optional)

Relay also supports the deposit address flow, which allows bridging without wallet connection or PSBT signing. When using deposit addresses, there are additional considerations:

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Block Confirmations

When using deposit addresses, Relay waits for 1 block confirmation before processing. Bitcoin’s block time averages ~10 minutes but varies significantly. blocks can arrive within minutes of each other or take 30-50 minutes.
When polling for deposit address transactions, allow for at least 2-3 blocks worth of time before considering a transaction stalled. You can monitor block times at mempool.space.

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Quote Requirements for Deposit Addresses

When using useDepositAddress: true with Bitcoin as origin:
  • The user address must be a valid Bitcoin address
  • The user address balance must exceed the quoted amount (otherwise returns INSUFFICIENT_FUNDS)
  • For indicative quotes, use a known high-balance address (“whale address”). The actual deposit can originate from any address.
curl -X POST "https://api.relay.link/quote/v2" \
  -H "Content-Type: application/json" \
  -d '{
    "user": "bc1q4vxn43l44h30nkluqfxd9eckf45vr2awz38lwa",
    "originChainId": 8253038,
    "originCurrency": "bc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmql8k8",
    "destinationChainId": 8453,
    "destinationCurrency": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913",
    "recipient": "0x03508bb71268bba25ecacc8f620e01866650532c",
    "tradeType": "EXACT_INPUT",
    "amount": "100000",
    "useDepositAddress": true,
    "refundTo": "bc1q4vxn43l44h30nkluqfxd9eckf45vr2awz38lwa"
  }'