“We don't have a single Rust developer in the room. … The two things that mattered most were the plan to do the thing and then the verification of the thing, because the actual implementation was Claude writing code. And so what we ended up doing was we literally built an entire fork of the entire API in Rust and then started running shadow traffic through it and verifying the outputs.”
Latent Space · AI Builders · October 2026
Context
Jiang was describing how Anthropic rewrote its Messages API from a CPU-hungry Python monolith into Rust to cope with a shortage of CPU capacity. Humans designed the distributed system; Claude wrote the code, and the Python and Rust versions were checked against each other on live traffic.
Transcript
I would add training. Training is probably usable. For sure, yeah. So there's
a different bucket, right? I'm sure they don't commingle that much.
…multi-region. We've done all these things we need to do. But we were like, we're running this Python monolith and it's like, it's like very CPU inefficient. And so what are we going to do to make the system more efficient? Yeah. So we chose Rust, which was a crazy decision at the time because there's a team of people, like on paper, it's obvious, but our team was like, we don't have a single, we don't have a single Rust developer in the room. Okay, it's just Viper. Exactly. Literally. And not only that, but yes, Claude is going to write the code. The humans like design the system, right? So like the humans are very involved in making sure at the end of the day, it's just like it's a distributed systems architecture, right? Like, and Claude can help you both with actually writing the code, but also helping those engineers like, you…
is all you need.
Yeah, literally. Low balancing feature files. I don't know. I never in my career would have had a team say like, yeah, yeah, cool. We're just going to people
or no Rust people.
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