Rivet vs Undertow

Rivet has consolidated around agentOS, a virtual operating system that gives agents a terminal, filesystem and networking on WebAssembly and V8 isolates inside a backend you already run, instead of a container or VM per agent session. The surrounding pieces are now in place: a package registry, an install path measured in microseconds, durable timezone-aware cron for actors, and an execution API that runs JavaScript and Python directly rather than shelling out to bash. Underneath it, the team is building its own storage layer — a zero-disk SQLite engine that keeps writes local-fast while cold pages tier out to object storage.

The argument Rivet keeps making is an economic one: a sandbox holds a whole container open while the agent sits idle waiting on inference, which is the cost structure isolates already solved. That case is no longer only Rivet's to make — Vercel's Eve and Flue both shipped agentOS support within two days of each other, which moves agentOS from a product surface toward a layer other vendors depend on. The recent work has shifted accordingly, from proving the runtime to filling in what a runtime needs to be depended on: execution APIs, scheduling, and now durable storage.

With the execution API and storage engine landing back to back, the next gap in the stack is state and data access for agents built on agentOS — expect the SQLite tiering work to surface as a product surface actors can call, not just an engineering post. A third platform adoption announcement in the same changelog format is the other pattern the entries support.