Skip to main content
Using the Wallet SDK? VTXO renewal is handled automatically. See Renewal & Recovery for details.
VTXOs are not permanent. Each one is created inside a batch output that has a defined expiration window. Before that window closes, the VTXO must be renewed or settled. This lifecycle is a deliberate design choice: expiration allows the operator to recycle capital efficiently and keeps the system’s onchain footprint compact.

​
Batch Expiry

Every batch output has a built-in expiration. When a batch expires, the operator gains the ability to sweep the underlying Bitcoin through the batch output’s sweep path. If a user’s VTXO is still active when the batch expires and they have not renewed it, the operator can claim those funds. In practice, the operator allows users to recover their VTXOs in a new batch (see VTXO Recovery), but the user loses the ability to enforce their claim unilaterally onchain. The solution is straightforward: participate in a batch swap before expiry. This creates a fresh VTXO in a new batch with a reset expiry timer, while inheriting full Bitcoin finality.

​
Liveness Requirements

The expiry mechanism creates liveness requirements for both operators and users.

​
Operator Liveness

Arkade uses a client-server architecture where operator uptime directly affects functionality. When the operator goes offline, users cannot initiate new transactions until the operator returns. However, existing funds remain completely safe through presigned exit transactions. Users retain the ability to exit unilaterally at any time, regardless of operator status. The operator faces strong economic incentives to maintain availability: downtime means lost fee revenue and user attrition.

​
User Liveness

Users must take action during the expiry window to maintain unilateral exit rights. They do this by participating in a batch swap, which renews their VTXOs with fresh expiry timestamps. Expired VTXOs get swept by the operator. While users may recover their funds through a new batch swap, they lose the ability to enforce ownership claims onchain. This creates a natural incentive to remain active and settle periodically.
In practice, the SDK and wallet software handle renewal automatically in the background. Users of well-built applications rarely need to think about expiry directly.

​
Delegation

Not every user can be online at the right moment. Arkade’s batch swap system lets users delegate the renewal of their virtual outputs to a third party without giving up custody.

​
How Delegation Works

Delegation is implemented at the VTXO level by embedding an additional spending path into the output script:
  • User + Operator (collaborative path). Standard cooperative spending.
  • User + timelock (exit path). Unilateral fallback.
  • User + Delegate + Operator (delegation path). Requires all three parties to sign.
The user presigns a batch registration request that specifies exactly which virtual outputs to renew and which outputs to create. The delegate can submit this request in a batch swap for the user. The delegate cannot change the terms or access funds beyond what the user signed.

​
Delegation Options

Wallet providers

Integrate automatic renewal into the application experience transparently.

Third-party services

Professional entities offering renewal with reliability guarantees.

Self-hosted

Run your own delegate/watchtower on a laptop, home node, or server.

​
Guarantees

Delegation preserves self-custody throughout:
  • User retains control. All delegation uses presigned batch registration requests. Funds remain self-custodial with unilateral exit always possible.
  • Pre-committed inputs and outputs. Each request defines exact inputs and outputs. Delegates cannot alter them or access funds beyond what was signed.
  • Strict timing constraints. Each request includes a time window that prevents delegates from submitting early to collect fees prematurely.

Previous: Settlement & Finality

Batch swaps, commitment transactions, and registration requests.

Next: Security & Trust Model

Unilateral exits, the Arkade Signer, and risk analysis.