Do paused sandboxes count toward the concurrency limit?

No. Only running sandboxes count toward your concurrency limit. Paused sandboxes are excluded, so you can keep many paused sandboxes around without affecting how many sandboxes you can run at the same time.

There is also no time limit on how long a sandbox can remain paused. Paused sandboxes are kept indefinitely — there is no automatic deletion or time-to-live — and you can resume them at any time.

E2B never kills paused sandboxes on its own. A paused sandbox is only removed when you explicitly call kill on it (either via sandbox.kill() or Sandbox.kill(sandboxId)).

For more details on pausing and resuming, see the Sandbox persistence page.