Boris Cherny

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396 appearances 1 recordings 1 series first heard Jul 2026 last heard 28 Jul

Boris Cherny’s voice in public audio — every appearance, attributed to the second.

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Y Combinator Startup Podcast · Boris Cherny: Building Claude Code · 28 Jul 2026 podcast

And a lot of the stuff in the system prompt was correcting for these behaviors that the model should have known, but it didn't.

Now Opus 5 just does it.

So yeah, we deleted 80% of the system prompt.

You can actually try deleting the rest of it too.

So when you run Cloud Code, you can just do like dash dash system prompt and set whatever system prompt you want if you want to experiment with it.

And another thing that you can try is simple mode.

So this is actually this kind of undocumented feature.

If you do quad code simple equals one, like this environment variable, and then you run quad, it'll delete all the system prompts, including from the tools.

And we actually use this as a sort of ablation to figure out, is the prompt useful?

And what's interesting is that the model is actually a little bit more intelligent without these prompts.

That's something that we've been finding.

But when you use quad code as a product, you do actually want some of these prompts because it helps you use the product and it helps the product behave and the model behave in the way that you would want when you're using it as a person.

That's right, that's right.

So to be fair, we don't delete the entire code base, but we do delete a lot.

So every time there's a new model, we try, in research we call this ablation.

And so what this means is you delete the entire system prompt, and then you bring it back line by line to figure out what is the impact of each individual line.

It's sort of like an eval, and you can kind of evaluate it, and ablation essentially it's an eval, but you delete things to figure out the impact.

And yeah, we do the same thing for tools.

We unship tools all the time.

We delete code in the harness all the time.

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