Sandbox Sidecars are now in public alpha

Sidecars are now in public alpha. A sidecar is an additional container that runs alongside your Sandbox on the same worker, sharing its lifecycle.

Sidecars enable new architectures such as running a custom proxy for network control, splitting complex multi-container workloads, or separating an agent harness from its tool calls. They're also the recommended way to do secrets injection today. Because sidecars share a worker with the main Sandbox, they offer low-latency networking, the ability to route all HTTPS traffic through the sidecar, and cheaper startup than a separate Sandbox.

See the sidecars guide for details.