# Opus 5 lets Claude Code remove instructions it no longer needs

Markdown copy of https://realalpha.app/s/opus-5-lets-claude-code-remove-instructions-it-no-longer/ on Real Alpha, the best minutes from long interviews with the people building AI. Cite and link the page, not this copy.

- Speaker: [Boris Cherny](https://realalpha.app/builders/boris-cherny/) · Boris Cherny is creator of Claude Code at Anthropic. · Created Claude Code at Anthropic and leads its team; previously spent about five years at Meta.
- Host: [Diana Hu](https://realalpha.app/people/diana-hu/) · Managing partner, Y Combinator · CTO of Escher Reality; after Niantic bought it, ran AR for Pokémon GO.
- Show: Lightcone
- Episode: [Boris Cherny: We Cut 80% of Claude Code’s Prompt](https://realalpha.app/v/qyPCVqFUyDo/), Jul 27, 2026
- Moment: 3:07 to 6:38 of the episode (4 min), playing on https://realalpha.app/s/opus-5-lets-claude-code-remove-instructions-it-no-longer/; the episode from there: https://realalpha.app/v/qyPCVqFUyDo/?t=187

## Quote

> “the model is actually a little bit **more intelligent without these prompts**.”
> — [Boris Cherny](https://realalpha.app/builders/boris-cherny/) at [4:50](https://realalpha.app/v/qyPCVqFUyDo/?t=290) · Lightcone

## Takeaways

1. Re-test prompts and tools with each new model.
2. Use ablations to measure what each instruction contributes.
3. Some prompts guide product behavior even if the model can work without them.

## About this segment

Boris Cherny says each model release triggers prompt and tool ablations; Opus 5 needed 80% less system prompt. Removing prompts can improve raw model performance, though product instructions still shape behavior.

From “Boris Cherny: We Cut 80% of Claude Code’s Prompt”, Jul 27, 2026. [Watch the full episode](https://realalpha.app/v/qyPCVqFUyDo/)

## Transcript

Transcribed by machine (Whisper) from the episode’s audio, so a word may be off here and there.

[3:19](https://realalpha.app/v/qyPCVqFUyDo/?t=199) injection, the other side of the coin is now the system prompt. Let's talk a bit about the new release. You actually deleted over 80% of the system prompt from CLAW code. Tell us more. about that? I think something that a lot of people might not realize is cloud code as a product and as a harness is just always changing. We're always adding stuff. We're always deleting stuff. Every time that a new model comes out, we delete a bunch of the system prompt, change a bunch of the system prompt. We change the set of tools all the time. We change the prompts for the tools all the time. And the reason is every model is very different. So something that you did for one model maybe three months ago, it just might not translate at all to the next model. And so one thing about Opus 5 is it's just really intelligent. And a lot of the stuff in the

[4:16](https://realalpha.app/v/qyPCVqFUyDo/?t=256) 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 cloud code simple equals one, like this environment variable, and then you run cloud, 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

[5:07](https://realalpha.app/v/qyPCVqFUyDo/?t=307) 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. I think the thing that's really fascinating in this era of building, basically you have built the best hardness in the world for Cloud, and that's Cloud Code.

[5:30](https://realalpha.app/v/qyPCVqFUyDo/?t=330) From what I'm hearing, for every model released, you basically delete all of the code base, delete all of the prompt, and start from scratch every time. That in the old world would have been not something started would have done for the product. It's like press delete every six months for everything. That's right. 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 the 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

[6:18](https://realalpha.app/v/qyPCVqFUyDo/?t=378) the harness all the time if you look at actually the code that's in the cloud code harness today almost all of it is about safety and permissions and static analysis and there's a bunch of ui code