“All told, it was about 136 billion tokens… if you were to use the public pricing of those models at those times, it came out to approximately $120,000. … About 20% of about 15 weeks, you end up with about three weeks of my time spread out over three months plus the token costs. And it's only getting cheaper.”
The Peterman Post · Software Engineering & Infra · November 2026
Context
Asked about the real cost of rewriting the GitHub Copilot runtime from TypeScript into Rust with agents, Toub gives the token count and list-price bill from his session logs, plus his own time.
Transcript
…different paths and looking at different things. And one of the biggest changes you can make is completely changing the model. And so the best way to get different opinions and focusing on different things that I found is by having different models. Especially than the one that I used initially.
So, you know, after you finish the rewrite, what was the concrete impact and the cost? So, if you look at it from a business perspective, what was the benefit and the cost of this project?
…of them are across different projects. And so I'm not, developers are no longer working on one thing at a time. So if you look at the percentage, just as a rough estimate. My time. If you look at the percentage of PRs that I was submitting over that same period, about a fifth of them, give or take, was to do with this project and about 80% was for other things. And so if you figure, you know, about 20% of about 15 weeks, you end up with about three weeks of my time spread out over three months plus the token costs. And it's only getting cheaper. The models are becoming cheaper at an astronomical rate. I think when OpenAI released, I'm not going to remember the exact things, but I think like 6.1 Sol is half the price of 6 Sol and 6 was half the price of 5.6 Sol. It's just getting cheaper and 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…
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…
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…
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