Rivet launches an open-source actor runtime for agents, with vendor benchmarks against sandboxes

Rivet's founders say each agent gets a long-lived actor with in-memory state, durable SQLite storage, and hibernation when idle, instead of its own sandbox. Writes are acknowledged once SSDs in two of three availability zones hold them, then batched to S3 in the background. In their published benchmark, run November 5 on Rivet 3.0.3 in Azure, a new actor cold-starts in 4.30 ms at the median (4.99 ms at p99), and a durable write takes 1.07 ms at p99. The founders say Amp moved its multiplayer agents to Rivet from Cloudflare Durable Objects; that is their account, and we did not verify it.

The headline comparison to sandboxes is weaker than the Rivet numbers. Rivet's own page says the E2B figures (1.27 s median cold start, 512 MiB memory) come from E2B's documentation and a third-party benchmark, not from the same setup, and calls them "separate benchmarks with different concurrency and environments." The 10x storage saving is a calculation from AWS list prices that excludes read and write costs. The page says the repository has scripts to reproduce the Rivet numbers; we did not run them.

Why it matters: The design question is whether an agent needs a full machine while it waits on a model. For agents that mostly call tools and APIs, an actor may be enough. A coding agent that has to run a compiler and tests still needs a process to run them in, and one commenter asked Rivet that exact question in the thread.