Summary
On October 8, 2026, Vercel changed Sandbox creation so that the API returns an already-started sandbox, folding the startup time that previously occurred during the first command into the create step for more consistent behavior.
What changed
Vercel Sandbox creation now returns a ready sandbox: the environment is fully started when the create call completes, rather than paying initialization latency on the first command executed in the sandbox.
Why it matters
Sandboxes are the execution substrate for running untrusted or agent-generated code, and hiding startup inside the first command made latency and behavior unpredictable for orchestrators. Returning a ready sandbox makes create-then-run timing deterministic, which matters for agent runtimes and CI-style pipelines that spin up many short-lived sandboxes and need predictable cold-start accounting.
Evidence excerpt
Sandbox creation is more consistent and now counts startup time that used to happen during the first command.