Vercel Sandbox can fork itself — branch an agent off a saved snapshot instead of rebuilding it

A changelog entry on 28 July 2026 added Sandbox.fork(), which starts a new sandbox from the source sandbox’s current snapshot and inherits its config and environment variables; anything passed to fork() overrides the inherited values. A running source contributes its latest saved state, not live in-memory state, and a source with no snapshot falls back to a fresh sandbox built from its runtime and config. Vercel says a fork takes about as long as creating a sandbox under the same limits, and names branching agents off a shared base, giving tenants template copies, and running parallel setup variations as the intended uses.

What it means A fan-out of agents over one prepared environment stops meaning N cold builds — the setup cost is paid once and forked.