Modal introduces Sidecars for Sandboxes
Modal announced Sidecars, a beta feature for its Sandboxes product, on October 1, 2026. Sidecars are isolated containers that run alongside a main Sandbox on the same host, intended to separate trusted services—such as credential injection, proxies, or agent-harness logic—from untrusted code.
Modal says the Sidecar and main Sandbox retain the same isolation boundary as separate Sandboxes, using gVisor or VMs depending on the runtime. They communicate over an internal bridge network. Modal’s internal benchmark reports Sidecar communication at least three times faster than communication between separate Sandboxes in the same region: 0.58 ms versus 2.6 ms p50 per call, and 1.4 ms versus 44 ms at p99. These are company-reported measurements, not independent results.
The announcement cites Ramp, which built a custom egress proxy alongside its Inspect coding-agent Sandboxes to monitor and control outbound traffic. Modal says Sidecars can be created dynamically through its SDK, share CPU and memory with the main Sandbox, and each have independent outbound network policy. The feature is in beta; the source does not establish independent security validation or performance across workloads.