A sandbox runs while it works

There is no lease to manage any more: a sandbox has no time limit unless you set one, runs for as long as it is busy and pauses itself when idle, until you stop it or credit runs out. Nothing needs extending, and code that extends, sets timeoutSeconds or calls keepAlive keeps working: a time limit you set is still kept. endsAt says when a sandbox will stop or pause by itself, and is null when it never will. The E2B, Daytona, Vercel, Blaxel, Modal and Runloop adapters do the same when your code sets no timeout. See the API.