On-chain payments
On-chain payments allow users to send bitcoin from their Ark wallet directly to any on-chain address. Offboarding uses this same process—the distinction is that offboards specifically refer to withdrawing whole VTXOs (or an entire Ark balance) back to the user's own on-chain wallet.
How on-chain payments work
When making an on-chain payment, the user cooperates with the Ark server to forfeit one or more VTXOs to deliver an on-chain output to the recipient's address. This process is atomic—neither the user nor the Ark server are exposed to counterparty risk.
The on-chain payment process
- Request payment: The user indicates to the Ark server that they want to make an on-chain payment, specifying the recipient's address and the amount.
- Construct transaction: The server constructs an on-chain transaction with the requested output and a connector output. If the payment amount doesn't exactly match the user's VTXO(s), any change is returned as a new VTXO.
- Check and sign: The user confirms that the requested output is present, then signs forfeit transactions linked to the connector.
- Broadcast transaction: The server signs and broadcasts the on-chain transaction.
- Wait for confirmation: The recipient's bitcoin eventually confirms on the blockchain.
Atomic guarantee
The connector in step 2 ensures atomicity. Because the user's forfeit is linked to the connector output, the forfeit is only valid once the payment transaction is broadcast. Either the payment completes and the forfeit is valid, or neither happens, eliminating any possibility of either party losing bitcoin during the operation.
Confirmation timing
On-chain payments are broadcast immediately upon completion. However, unlike Ark payments and Lightning payments (which are near-instant), the recipient must wait for the transaction to confirm on the blockchain. Confirmation speed depends on the on-chain fee selected by the user or wallet app.
On-chain payments are no longer processed in rounds
Previously, on-chain payments were handled during rounds. Following the hArk update in January 2026, on-chain payments are now processed immediately when initiated.
On-chain payment fees
On-chain payments on Bark involve several cost components:
- Liquidity costs: The Ark server must immediately deploy bitcoin to fund the on-chain output and wait for the forfeited VTXO(s) to expire before it can sweep the bitcoin. Costs depend on the amount paid, VTXO age, and the server's cost of capital.
- On-chain fee: The cost of confirming the transaction on-chain.
- Ark server fees: The Ark server may charge additional fees to cover general operational costs.