So, the simulator only works if it knows what "correct" looks like and what kinds of failures to throw at the code, right? Who decided those two things? Was it the same agent that wrote the code? Were those human-written, or did they fall out of the formal specs?
You had three things that could each say "this is right", the end-to-end tests, the formal model, and how the old Go version behaved. When they disagreed, which one did you trust? Did the test ever turn out to be the thing that was wrong?
When the simulator caught something before release, was it usually the code that was wrong, or the definition of correct?
Feels like there's some really useful insights about best practices for coding with agents. I wonder if the Bun team used a similar approach if they still would have switched.
At the moment the reverse is true though, the simulator and what we've captured as ground truth for the desired design has been refined enough in tests and specs that the code is often the one implicated, and most of the bugs have been in code related to caching correctness and are only exposed through soak testing.
In opposition to Anthropic/Bun, we mostly used a hands-on approach to the rewrite and took the opportunity to capture the original design of Antfly into specs and any missing tests one subsystem at a time so we didn't strive to be as hands-off as "let Claude hill-climb on the tests". Especially since the system as a whole is far more dynamic and depends more on scalability, distributed systems stuff than Bun required!
kingcauchy•3d ago
Thought it is interesting to juxtapose to the Bun rewrite from Anthropic and wanted to talk about why we went the other way! Would love to talk about our process or the technology!
Benchmarks against are linked in the article but here they are again for posterity https://antfly.io/releases/v0.2
esafak•14m ago