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Blaxel sandboxes operate in active and standby states. These states determine which resources are billed and how quickly a sandbox can resume.

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Active mode

A sandbox stays active while it has an active connection. In active mode, you are charged for allocated memory and storage. Blaxel allocates CPU based on your selected memory allocation. CPU is not charged separately. Active connection behavior includes:
  • HTTP, WebSocket, or TCP connections with data flow keep a sandbox active
  • Idle connections, such as WebSockets with no data flow, have a 15-minute timeout
  • After 15 minutes with no data transmission, the sandbox transitions to standby
See standby control for ways to manage connections and activity.

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Standby mode

Without active connections, a sandbox transitions to standby in approximately 15 seconds. During the transition:
  • Blaxel snapshots the complete state, including the filesystem and running processes
  • You are not charged for CPU or memory while the sandbox is in standby
  • You are charged only for snapshot and volume storage
  • Reconnecting restores the sandbox in under 25 ms with its processes preserved

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Common issues preventing standby

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Missing sandbox API

A missing or outdated sandbox API is the most common reason a sandbox fails to enter standby. The sandbox API is required for correct shutdown behavior. To correct the configuration:
  1. Use the latest sandbox API in your Dockerfile.
  2. Copy the binary into your image:
  3. Start the sandbox API first in your entrypoint and wait for it to become ready on port 8080 before starting other processes.
  4. Delete and recreate the sandbox after updating the image.

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Preview URL connections

Deployed preview URLs do not maintain persistent connections and do not prevent standby. You do not need to recreate previews to allow a sandbox to enter standby. Each incoming request through a preview URL wakes the sandbox.

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Process keep-alive

Process keep-alive controls automatic hibernation. Starting a process with keepAlive: true in TypeScript or keep_alive: True in Python keeps the sandbox active until the process completes or times out. The default timeout is 600 seconds. Set the timeout to 0 for a process that should run until it completes naturally.

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Monitor sandbox state

The API reports DEPLOYED for both active and standby sandboxes. Use these methods to distinguish them:
  • Check CPU or memory charts in the Blaxel Console. A value of 0% indicates that the sandbox was in standby
  • Use Billing Explorer to inspect compute runtime charges, measured in GB-seconds
  • Treat continuous compute runtime charges as a sign that the sandbox may be stuck in active mode

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Troubleshoot continuous billing

If a sandbox that should be idle incurs continuous compute charges:
  1. Verify that the sandbox API is installed and running.
  2. Close every connection when it is idle.
  3. Check for background processes that keep connections open.
  4. Delete and recreate the sandbox after correcting the sandbox API.
A correctly configured sandbox incurs compute charges only while it actively processes requests.

Sandbox standby control

Manage active connections and automatic standby behavior.

Process keep-alive

Keep a sandbox active while selected processes run.
Last modified on October 5, 2026