Actors with photographic memory and no pod bloat

What it does

Rivet is an open-source actor framework built in Rust that spawns long-running, lightweight processes for stateful workloads. Each actor keeps state in-memory—persisted automatically to co-located SQLite or an external database—and handles its own queues, workflows, scheduling, and WebSocket broadcasts. You can run it as a local TypeScript library during development, self-host the engine via a single Rust binary or Docker container backed by Postgres or FoundationDB, or offload scaling to Rivet Cloud’s managed global edge network.

The interesting bit

The engine is a Rust monolith split into specialized crates—Pegboard for actor orchestration, Gasoline for durable execution, Guard for traffic routing, and Epoxy, a multi-region KV store built on EPaxos. The README’s benchmark methodology is unusually detailed, breaking down AWS EKS node costs and containerd shim overhead to justify claims of ~20 ms cold starts and ~0.6 KB per-actor memory overhead.

Key highlights

• Claims ~20 ms cold starts and ~0.6 KB memory per actor instance, with methodology comparing Node.js/FoundationDB against Kubernetes pods and EC2 instances.
• Built-in observability includes a real-time SQLite viewer, workflow step inspector, event monitor, and REPL.
• Supports multiple runtimes (Node.js, Bun, Deno) and frameworks (React, Next.js, Hono, Express, tRPC) via the TypeScript-first RivetKit.
• Self-hosting options include a single Rust binary or Docker container with Postgres, filesystem, or FoundationDB backends.
• Experimental Rust and Python client libraries ship in the same monorepo.

Caveats

• Rust and Python clients are explicitly marked experimental; the developer experience is TypeScript-first.
• The “$0 idle cost” and “infinite” horizontal scale figures assume Rivet Cloud’s serverless platform, not the self-hosted engine.

Verdict

Worth a look if you need per-user or per-session stateful services—like AI agents or collaborative editors—with Durable Objects-style semantics and open-source portability. Skip it if you require mature non-TypeScript SDKs today or if your stack is strictly stateless.