“First, it wouldn't have happened. And I'm actually serious. For this particular thing, it wouldn't have happened because by the time we were done, we would have ported the wrong thing. This space is moving so fast that we would have basically never finished.”
The Peterman Post · Software Engineering & Infra · November 2026
Context
Asked what this rewrite would have looked like before AI, Toub says a team would have needed a year or two for hundreds of thousands of lines, and new code kept arriving the whole time.
Transcript
…cheaper and cheaper. And the models are also getting better and better and better, which means that the amount of time that I need to put in to steer the models to do the right thing is also decreasing. And so the costs of these ports, the cost of these migrations is only getting cheaper over time.
Wow. So three weeks of, I guess, of developers' time plus $120,000, you're able to rewrite the entire code base. If you were to scope this out pre-AI, let's say you wanted to undertake this, what would that look like?
First, it wouldn't have happened. And I'm actually serious, like for this particular thing, it wouldn't have happened because by the time we were done, we would have ported the wrong thing. This space is moving so fast that we would have basically never finished, I think. In fact, you can kind of see that in the charts in the blog post in that for a good portion of the porting effort, the amount of Rust is increasing and the amount of TypeScript is largely remaining the same, but increasing a little bit. And that's because as the port was happening, there was just a huge amount of new functionality coming into the repo, right? And at the beginning of the porting effort, because the majority of the code base was TypeScript, the majority of the new incoming code was also TypeScript. By the end of the project, where the majority of the code base was Rust, the majority of the new incoming code was Rust. But if you look at like the first half of the graph, where we're generally 50% or less Rust, the amount of TypeScript was doing this, even as…
It sounds like, at least for this type of work where it's super what we want is very obvious and encoded somewhere in the existing functionality. So like this type of work is at least one order of magnitude cheaper, maybe even more. I mean, if you had a team of engineers and they're, you know…
Yes. And the bill ended up being larger than I expected. Mostly because the line count ended up being larger than I expected. I hadn't fully factored in the growth rate of how much incoming code there would be. So this was, you know, there were a few things. I think I did a lot of things right. I…
So after having gone through this process, if there was a software engineer out there on some team considering doing some sort of rewrite, what criteria should they look for to decide if it's worth undertaking it or not?
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