Rivet, a YC W23 Company, Runs Agent Actors on S3 and Claims 72 KB Each
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Rivet, a YC W23 Company, Runs Agent Actors on S3 and Claims 72 KB Each
The Apache 2.0 orchestrator says an actor cold-starts in 4.99 ms at p99. Every figure is Rivet's own, and the Launch HN thread questioned both the premise and the AWS bill.
Rivet, a Y Combinator W23 company, launched an open-source orchestrator for AI agents on Hacker News on November 5, 2026, built around "actors" that keep state in memory and in SQLite and persist durable data to object storage such as S3. The repository is Apache 2.0 licensed and showed 6.9k stars and 6,335 commits on main when we read it. Stars measure interest, not adoption.
The Launch HN post is by Nathan Flurry and a co-founder named Nicholas, and it reached 122 points. It pitches Rivet as an open-source, self-hostable alternative to Cloudflare Durable Objects.
What a Rivet actor is
An actor is a long-lived process, one per agent, user, session or tenant, with in-memory state, a SQLite database, WebSockets and scheduling. Idle actors hibernate and wake on the next request. The control plane is written in Rust, and its only required dependency is object storage, which can be an S3-compatible bucket, Google Cloud Storage, Azure Blob Storage or a local filesystem. SDKs exist for TypeScript and Rust, with Python and Swift marked experimental.
The founders say Rivet began as game-server orchestration and previously ran on FoundationDB. Customers stored far more data than expected, such as session transcripts and filesystems, and paid for SSDs that sat mostly idle. Writes are now acknowledged once two of three availability zones hold them on SSD, then batched to S3 in the background, which keeps S3 off the write path.
The vendor-supplied numbers
The README compares an actor against a sandbox, using figures from E2B's billing documentation and a ComputeSDK benchmark. The comparison is Rivet's own and no independent party is named as having reproduced it.
| Measure | Rivet actor | Sandbox baseline |
|---|---|---|
| Cold start, p99 | 4.99 ms | 1.70 s |
| Memory per instance | 72 KB | 512 MiB |
| Durable SQLite write, p99 | 1.07 ms | not stated |
The launch post gives the cold start as 4.9 ms and the README as 4.99 ms. The README also claims storage about 10.4x cheaper than replicated SSD, and the post says about 10x cheaper than EBS gp3. The founders also say Amp migrated from Durable Objects in a weekend and deploys on-prem, a customer claim we could not check.
- Rivet actor4.99 ms
- Sandbox1700 ms
Source: Rivet README (rivet-dev/rivet), accessed 2026-11-12
What commenters pushed back on
The thread was less settled than the benchmarks. A commenter named esafak wrote that "orchestration speed ain't one of them," arguing that speed is not the pain point and suggesting a durability pitch instead. ATechGuy2 said "many sandboxing startups would disagree" with the cost framing and asked for numbers. Flurry replied with benchmark links and said there is no one-size-fits-all answer.
chicagobuss raised cross-AZ traffic costs on AWS, saying they "might surprise people." A co-founder, Tanjreeve in the thread, acknowledged the tradeoff and mentioned S3 Express zones as an alternative. takeitwhen warned that resuming is unsafe if tool results live only in memory or temp files, since an agent may "invent a confident continuation" after waking. sebastienburel asked how hibernation treats an actor with an outstanding async request.
Usability drew complaints too. minraws called the experience "horrible ux atm," and serjester said the homepage left a reader with a Ph.D. unsure what it does.
What is not settled
The README says Dynamic Apps is a preview feature and recommends a separate sandbox for running untrusted code an agent writes. The Launch HN post gives no price list. It names three deployment routes: a single self-hosted binary with S3, Rivet Cloud dedicated clusters, and bring-your-own-cloud. For another young open-source agent tool and its own claims, see our piece on Atuin Threads, and for another YC company selling to agents, Pomerado.
The README lists no production track record or operating guide. Python and Swift SDK status will show whether non-TypeScript teams can adopt it.
Sources
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