Claude Code And Its Creator Boris Cherny

Introduction

"At Anthropic, the way that we thought about it is we don't build for the model of today. We build for the model six months from now." — "All of Claude Code has just been written and rewritten and rewritten and rewritten over and over and over. There is no part of Claude Code that was around 6 months ago." — "Maybe in a month, no more need for plan mode in a month. Oh my god."

HOST: Welcome to another episode of the Lightcone and today we have an extremely special guest, Boris Cherny, the creator engineer of Claude Code. Boris, thanks for joining us.

BORIS: Thanks for having me.

HOST: Thanks for creating a thing that has taken away my sleep for about 3 weeks straight. I am very addicted to Claude Code and it feels like rocket boosters. Has it felt like this for people — like for you know months at this point?

BORIS: I think it was like end of November is where a lot of my friends said like something changed. I remember for me I felt this way when I first created Claude Code and I didn't yet know if I was on to something. I kind of felt like I was on to something and then that's when I wasn't sleeping. Yeah. And that was just like three straight months. This was September 2024. It was like three straight months. I didn't take a single day vacation. Worked through the weekends. Worked every single night. I was just like, "Oh my god, this is — I think this is going to be a thing. I don't know if it's useful yet because it couldn't actually code yet."

I. The Most Surprising Moment in the Rise of Claude Code

HOST: If you look back on those moments to now, like what would be the most surprising thing about this moment right now?

BORIS: It's unbelievable that we're still using a terminal. That was supposed to be the starting point. I didn't think that would be the ending point. And then the second one is that it's even useful because at the beginning it didn't really write code. Even in February when we GA'd it wrote maybe like 10% of my code or something like that. I didn't really use it to write code. It wasn't very good at it. I still wrote most of my code by hand. So the fact that our bets paid off and it got good at the thing that we thought it was going to get good at because it wasn't obvious. At Anthropic, the way that we thought about it is we don't build for the model of today. We build for the model 6 months from now. And that's actually like still my advice to founders that are building on LLMs — just try to think about what is that frontier where the model is not very good at today because it's going to get good at it and you just have to wait.

II. How Boris Came Up with the Idea for Claude Code

HOST: Going back though, do you remember when you first got the idea? Can you just talk us through that? Like was it some spark or what was even the first version of it in your mind?

BORIS: You know, it's funny. It was so accidental that it just kind of evolved into this. As Anthropic I think for Anthropic the bet has been coding for a long time and the bet has been the path to safe AGI is through coding and this has kind of always been the idea and the way you get there is you teach the model how to code then you teach it how to use tools then you teach it how to use computers. And you can kind of see that because the first team that I joined at Anthropic it was called the Anthropic Labs team and it produced three products — it was Claude Code, MCP, and the desktop app. So you can kind of see how these weave together.

The particular product that we built — no one asked me to build a CLI. We kind of knew maybe it was time to build some kind of coding product because it seemed like the model was ready, but no one had yet really built the product that harnessed this capability. So like still there's this insane feeling of product overhang. But at the time it was just even crazier because no one had built this yet. And so I started hacking around and I was like, "Okay, we build a coding product. What do I have to do first? I have to understand how to use the API because I hadn't used the Anthropic API at that point." And so I just built a little terminal app to use the API. That's all that I did. And it was a little chat app because you know like you think about the AI applications of the time and for non-coders today what are most people using is just a chat app. So that's what I built. And it was in a terminal. I can ask questions. I give answers. Then I think tool use came out. I just wanted to try out tool use because I don't really understand what this is. I was like tool use is cool. Is this actually useful? Probably not. Let me just try it.

HOST: You built it in terminal just because it was the easiest way to get something up and running.

BORIS: Yes. Because I didn't have to build a UI.

HOST: Okay. It was just me at that point. The IDEs, Cursor, Windsurf taking off. Were you under any pressure or getting lots of suggestions of, hey, we should build this out as a plugin or as a fully featured IDE itself?

BORIS: There was no pressure because we didn't even know what we wanted to build. Like the team was just in explore mode. We knew vaguely we wanted to do something in coding, but it wasn't obvious what. No one was high confidence enough. That was my job to figure out. And so I gave the model the bash tool. That was the first tool that I gave it just because I think that was literally the example in our docs. I just took the example. It was in Python. I just ported it to TypeScript because that's how I wrote it. I didn't know what the model could do with bash. So I asked it to read a file. It could cat the file. So that was cool. And then I was like, "Okay, what can you actually do?" And I asked, "What music am I listening to?" It wrote some AppleScript to script my Mac and look up the music in my music player.

HOST: Oh my god.

BORIS: And this was Sonnet 3.5. And I didn't think the model could do that. And that was my first — I think ever — feel-the-AGI moment where I was just like, "Oh my god, the model — it just wants to use tools. That's all it wants."

III. The Elegant Simplicity of Terminals

HOST: That's kind of fascinating. I mean it's very contrarian that Claude Code works so well in such an elegant simple form factor. Terminals have been around for a really long time and that seemed to be like a good design constraint that allowed a lot of interesting developer experiences. It doesn't feel like working. It just feels fun as a developer. I don't think about files where everything is and that came by accident almost.

BORIS: Yeah, it was an accident. I remember after the terminal started to take off internally — and honestly after building this thing I think like 2 days after the first prototype I started giving it to my team just for dogfooding because if you come up with an idea and it seems useful the first thing you want to do is give it to people to see how they use it. And then I came in the next day and then Robert who sits across from me who's another engineer he just had Claude Code on his computer and he was using it to code. I was like, "What are you doing? This thing isn't ready. It's just a prototype." But yeah, it was already useful in that form factor.

And I remember when we did our launch review to kind of launch Claude Code externally, this was in December, November, something like that in 2024. Dario asked and he was like, "The usage chart internally like the DAU chart is vertical. Are you forcing engineers to use it? Why are you mandating them?" And I was just like, "No, no, we didn't. I just posted about it and they've just been telling each other about it." Honestly, it was just accidental. We started with the CLI because it was the cheapest thing and it just kind of stayed there for a bit.

IV. The First Use Cases

HOST: So in that 2024 period, how were the engineers using it? Were they sort of shipping code with it yet or were they using it in a different way?

BORIS: The model was not very good at coding yet. I was using it personally for automating git. I think at this point I've probably forgotten most of my git because Claude Code has just been doing it for so long. But yeah, automating bash commands — that was a very early use case and like operating Kubernetes and things like this. People were using it for coding. There were some early signs of this. I think the first use case was actually writing unit tests because it's a little bit lower risk and the model was still pretty bad at it but people were figuring it out and they were figuring out how to use this thing.

And one thing that we saw is people started writing these markdown files for themselves and then having the model read that markdown file. And this is where CLAUDE.md came from. Probably the single for me biggest principle in product is latent demand. And just every bit of this product is built through latent demand after the initial CLI. And so CLAUDE.md is an example of that.

There's this other general principle that I think is maybe interesting where you can build for the model and then you can build scaffolding around the model in order to improve performance a little bit and depending on the domain you can improve performance maybe 10, 20% something like that and then essentially the gain is wiped out with the next model. So either you can build the scaffolding and then get some performance gain and then rebuild it again or you just wait for the next model and then you kind of get it for free. The CLAUDE.md and kind of the scaffolding is an example of that and really I think that's why we stayed in the CLI is because we felt there is no UI we could build that would still be relevant in 6 months because the model was improving so quickly.

V. What's in Boris' CLAUDE.md?

HOST: Earlier we were saying like we should compare CLAUDE.md's but you said something very profound which is yours is actually very short which is almost like the opposite of what people might expect. Why is that? What's in your CLAUDE.md?

BORIS: Okay so I checked this before we came. So my CLAUDE.md has two lines. The first line is whenever you put up a PR, enable automerge. So as soon as someone accepts it, it's merged. That's just so I can code and I don't have to kind of go back and forth with code review or whatever. And then the second one is whenever I put up a PR, post it in our internal team stamps channel. Just so someone can stamp it and I can get unblocked. And the idea is every other instruction is in our CLAUDE.md that's checked into the codebase and it's something our entire team contributes to multiple times a week. And very often I'll see someone's PR and they make some mistake that's totally preventable and I'll just literally tag Claude on the PR. I'll just do like add Claude, you know, add this to the CLAUDE.md and I'll do this many times a week.

HOST: Do you have to compact the CLAUDE.md? Like I definitely reached a point where I got the message at the top saying your CLAUDE.md is like thousands of tokens now. What do you do when you guys hit that?

BORIS: So our CLAUDE.md is actually pretty short. I think it's like a couple thousand tokens maybe something like that. If you hit this my recommendation would be delete your CLAUDE.md and just start fresh.

HOST: Interesting.

BORIS: I think a lot of people try to over-engineer this and really the capability changes with every model. And so the thing that you want is do the minimal possible thing in order to get the model on track. And so if you delete your CLAUDE.md and then the model is getting off track, it does the wrong thing. That's when you kind of add back a little bit at a time. And what you're probably going to find is with every model, you have to add less and less.

For me, I consider myself a pretty average engineer to be honest. I don't use a lot of fancy tools. I don't use Vim. I use VS Code because it's simpler.

HOST: Wait, really? I would have assumed that because you built this in the terminal that you were sort of like a diehard terminal Vim-only person. You know, screw those VS Code people.

BORIS: Well we have people like that on the team. There's Adam Wolf for example, he's on the team, he's like "you will never take Vim from my cold dead hands." So there's definitely a lot of people like that on the team and this is one of the things that I learned early on is every engineer likes to hold their dev tools differently. They like to use different tools. There's just no one tool that works for everyone. But I think also this is one of the things that makes it possible for Claude Code to be so good because I kind of think about it as what is the product that I would use that makes sense to me and so to use Claude Code you don't have to understand Vim you don't have to understand tmux you don't have to know how to SSH you don't have to know all the stuff you just have to open up the tool and it'll guide you it'll do all this stuff.

VI. How Do You Decide the Terminal's Verbosity?

HOST: How do you decide how verbose you want the terminal to be? Like sometimes you have to go Control-O and check it out and is it like internal bikeshed battles around longer, shorter? I mean every user probably has an opinion. How do you make those sorts of decisions?

HOST: What's your opinion? Is it too verbose right now?

HOST: Oh, I love the verbosity because basically sometimes it just goes off the deep end and I'm watching and then I can just read very quickly and it's like, "Oh, no, no, it's not that." And then I escape and then just stop it and then it just stops an entire bug farm as it's happening. I mean, that's usually when I didn't do plan mode properly.

BORIS: This is something that we probably change pretty often. I remember early on, this is maybe six months ago, I tried to get rid of bash output just internally just to summarize it because I was like these giant long bash commands, I don't actually care. And then I gave it to Anthropic employees for a day and everyone just revolted. "I want to see my bash" because it actually is quite useful for, you know, like for something like git output, maybe it's not useful, but if you're running Kubernetes jobs or something like this, you actually do want to see it.

We recently hid the file reads and file searches. So you'll notice instead of saying, you know, read foo.md it says, you know, read one file, searched one pattern. And this is something I think we could not have shipped six months ago because the model just was not ready. It would have, you know, it still read the wrong thing pretty often. As a user, you still had to be there and kind of catch it and debug it. But nowadays, I just noticed it's on the right track almost every time. And because it's using tools so much, it's actually a lot better just to summarize it.

But then we shipped it. We dogfooded it for like a month and then people on GitHub didn't like it. So there was a big issue where people were like "no, I want to see the details" and that was really great feedback. And so we added a new verbose mode and so that's just in slash config you can enable verbose mode and if you want to see all the file outputs you can continue to do that. And then I posted on the issue and people still didn't like it which is again awesome because my favorite thing in the world is just hearing people's feedback and hearing how they actually want to use it. And so we just iterated more and more and more to get that really good and to make it the thing that people want.

HOST: I'm amazed how much I enjoy fixing bugs now. And then all you have to do is have really good logging and then even just say like hey check out this particular object it messed up in this way and it searches the log. It figures everything out. It can go into your — you can make a production tunnel and it'll look at your production DB for you. It's like this is insane. Bug fixing is just going to Sentry, copy markdown. Pretty soon it's just going to be straight MCP. It's like an auto-bug-fixing and test-making sort of — what's the new term they call it, like a making a startup factory.

HOST: Oh yeah. Right. There's all these concepts now of rather than having to review the code — I'm old school, so I like the verbosity. I like to say, "Oh, well, you're doing this, but I want you to do that." Right? But there's a totally different school of thought now that says anytime a real human being has to look at code, that's bad.

BORIS: Yeah. Yeah. Which is fascinating. I think Dan Shipper talks about this a lot as kind of whenever you see the model make a mistake try to put it in the CLAUDE.md, try to put it in skills or something like that so it's reusable. But I think there's this meta point that I actually struggle with a lot. And people talk about agents can do this, agents can do that, but actually what agents can do, it changes with every single model. And so sometimes there's a new person that joins the team and they actually use Claude Code more than I would have used it. And I'm just constantly surprised by this.

Like for example, we had a memory leak and we were trying to debug it. And by the way, Jared Sumner has just been on this crusade killing all the memory leaks and it's just been amazing. But before Jared was on the team, I had to do this and there was this memory leak. I was trying to debug it. And so I took a heap dump. I opened it in DevTools. I was looking through the profile. Then I was looking through the code and I was just trying to figure this out. And then another engineer on the team, Chris, he just asked Claude Code. He was like, "Hey, I think there's a memory leak. Can you run this?" And then try to figure it out. And Claude Code took the heap dump. It wrote a little tool for itself to analyze the heap dump. And then it found the leak faster than I did. And this is just something I have to constantly relearn because my brain is still stuck somewhere six months ago at times.

VII. Beginner's Mindset Is Key as the Models Improve

HOST: So what would be some advice for technical founders to really become maximalists at the latest model release? It sounds like people fresh off of school or that don't have any assumptions might be better suited than maybe sometimes engineers who have been working at it for a long time. And how do the experts get better?

BORIS: I think for yourself it's kind of beginner mindset and I don't know maybe just like humility. I feel like engineers as a discipline we've learned to have very strong opinions and senior engineers are kind of rewarded for this. In my old job at a big company when I hired architects and this type of engineer you look for people that have a lot of experience and really strong opinions. But it actually turns out a lot of this stuff just isn't relevant anymore and a lot of these opinions should change because the model is getting better. So I think actually the biggest skill is people that can think scientifically and can just think from first principles.

HOST: How do you screen for that when you try to hire someone now for your team?

BORIS: I sometimes ask about what's an example of when you're wrong. It's a really good one. Some of these classic behavioral questions — not even coding questions — I think are quite useful because you can see if people can recognize their mistake in hindsight, if they can claim credit for the mistake and if they learned something from it. And I think a lot of these very senior people especially — there are some founder types like this but I think founders in particular are actually quite good at it. But other people sometimes will never really take the blame for a mistake. But I don't know, for me personally I'm wrong probably half the time. Like half my ideas are bad and you just have to try stuff and you try a thing, you give it to users, you talk to users, you learn, and then eventually you might end up at a good idea. Sometimes you don't. And this is the skill that I think in the past was very important for founders, but now I think it's very important for every engineer.

HOST: Do you think you would ever hire someone based on the Claude Code transcript of them working with the agent? Because we're actively doing that right now. We just added as a test — you can upload a transcript of you coding a feature with Claude Code or Codex or whatever it is. Personally, I think it's going to work. I mean, you can figure out how someone thinks, like whether they're looking at the logs or not, can they correct the agent if it goes off the rails? Do they use plan mode? When they use plan mode, do they make sure that there are tests? All of these different things — do they think about systems? Do they even understand systems? There's just so much that's embedded in that. I just want a spider web graph, you know, like in those video games like NBA 2K. It's like, oh, this person's really good at shooting or defense. You could imagine a spiderweb graph of someone's Claude Code skill level.

HOST: What would the skills be? What would those be?

HOST: I mean, I think it's like systems, testing, user behavior. There's got to be a design part, product sense, maybe also just automating stuff.

BORIS: My favorite thing in CLAUDE.md for me is I have a thing that says for every plan decide whether it's overengineered, underengineered, or perfectly engineered and why. I think this is something that we're trying to figure out too.

VIII. Hyper Specialists vs Hyper Generalists

BORIS: When I look at engineers on the team that I think are the most effective, there's essentially two — it's very bimodal. There's one side where it's extreme specialists. And so I named Jared before, he's a really good example of this and kind of the Bun team is a really good example. Just hyper specialist. They understand dev tools better than anyone else. They understand JavaScript runtime systems better than anyone else. And then there's the flip side of kind of hyper generalists and that's the rest of the team. And a lot of people they span product and infra or product and design or product and user research, product and business. I really like to see people that just do weird stuff. I think that's one of these things that was kind of a warning sign in the past because it's like can these people actually build something useful?

HOST: That's the litmus test.

BORIS: Yeah, that's what it must be. But nowadays — for example an engineer on the team Daisy, she was on a different team and then she transferred onto our team and the reason that I wanted her to transfer is she put up a PR for Claude Code a couple weeks after she joined or something and the PR was to add a new feature to Claude Code and then instead of just adding the feature what she did is first she put up a PR to give Claude Code a tool so that it can test an arbitrary tool and verify that that works. And then she put up that PR and then she had Claude write its own tool instead of herself implementing it. And I think it's this kind of out of the box thinking that is just so interesting because not a lot of people get it yet.

We use the Claude Agents SDK to automate pretty much every part of development. It automates code review, security review. It labels all of our issues. It shepherds things to production. It does pretty much everything for us. But I think externally I'm seeing a lot of people start to figure this out, but it's actually taken a while to figure out how do you use LLMs in this way? How do you use this new kind of automation? So it's kind of a new skill.

HOST: I guess one of the funnier things that I've been having office hours with various founders about is you have sort of the visionary founder who has the idea, they've built this crystal palace of the product that they want to build. They've totally loaded in their brain who the user is and what they feel and what they're motivated by and then they're sitting in Claude Code and they can do like 50x work and then but they have engineers who work for them who don't have the crystal memory palace of the platonic ideal of the product that the founder has and they can only do like 5x work. Are you hearing stories like that?

BORIS: There's usually a person who's the core designer of a thing and they're just trying to blast it out of their brain.

HOST: What's the nature of teams like that? It seems like that's almost a stable configuration. You're going to have the visionary who now is unleashed, but maybe going back to the top of it, I'm experiencing this right now. I was like, "Oh, well, I'm only a solo person and I need to eat and sleep and I have a whole job. How am I going to do this?"

IX. The Vision for Claude Teams

HOST: We just launched Claude Teams. What's the vision for Claude Teams?

BORIS: Just collaboration. There's this whole new field of agent topologies that people are exploring. What are the ways that you can configure agents? There's this one sub-idea which is uncorrelated context windows. And the idea is just multiple agents, they have fresh context windows that aren't essentially polluted with each other's context or their own previous context. And if you throw more context at a problem, that's like a form of test-time compute. And so you just get more capability that way. And then if you have the right topology on top of it, so the agents can communicate in the right way, they're laid out in the right way, then they can just build bigger stuff.

And so Teams is kind of one idea. There's a few more that are coming pretty soon. And the idea is just maybe it can build a little bit more. I think the first kind of big example where it worked is our plugins feature was entirely built by a swarm over a weekend. It just ran for a few days. There wasn't really human intervention. And plugins is pretty much in the form that it was when it came out.

HOST: How did you set that up? Did you spec out the outcome that you were hoping for and then let it figure out the details and let it run?

BORIS: Yeah. An engineer on the team just gave Claude a spec and told Claude to use an Asana board and then Claude just put up a bunch of tickets on Asana and then spawned a bunch of agents and the agents started picking up tasks. The main Claude just gave instructions and they all just figured it out — independent agents that didn't have the context of the bigger spec.

X. Subagents

BORIS: If you think about the way that our agents actually work nowadays — and I haven't pulled the data on this but I would bet the majority of agents are actually prompted by Claude today in the form of sub-agents because a sub-agent is just a recursive Claude Code. That's all it is in the code. And it's just prompted by — we call her mama Claude — and that's all it is. And I think probably if you look at most agents they're launched in this way.

HOST: My Claude Insights just told me to do this more for debugging. So I spend a lot of time on debugging and it would just be better to have multiple sub-agents spin up and debug something in parallel. And so then I just added that to my CLAUDE.md to be like, hey, next time you try and fix a bug, have one agent that looks in the log, one that looks in the code path. That just seems sort of inevitable.

HOST: For weird scary bugs, I try to fix bugs in plan mode and then it seems to use the agents to sort of search everything. Whereas when you're just trying to do it inline, it's like, okay, I'm going to do this one task instead of search wide.

BORIS: This is something I do all the time too. I just say — if the test seems kind of hard, this kind of research task, I'll calibrate the number of sub-agents I ask it to use based on the difficulty of the task. So if it's really hard, I'll say use three or maybe five or even 10 sub-agents, research in parallel and then see what they come up with.

HOST: I'm curious. So then why don't you put that in your CLAUDE.md file?

BORIS: It's kind of case by case. CLAUDE.md — what is it? It's just a shortcut. If you find yourself repeating the same thing over and over, you put it in the CLAUDE.md. But otherwise, you don't have to put everything there. You can just prompt Claude.

XI. A World Without Plan Mode?

HOST: Are you also in the back of your mind thinking that maybe in six months, you won't need to prompt that explicitly? Like the model will just be good enough to figure out on its own.

BORIS: Maybe in a month.

HOST: No more need for plan mode in a month. Oh my god.

BORIS: I think plan mode probably has a limited lifespan.

HOST: Interesting. That's some alpha for everyone here. What would the world look like without plan mode? Do you just describe it at the prompt level and it would just do it? One-shot it?

BORIS: Yeah, we've started experimenting with this because Claude Code can now enter plan mode by itself. I don't know if you guys have seen that. So, we're trying to get this experience really good. So, it would enter plan mode at the same point where a human would have wanted to enter it. So, I think it's something like this, but actually plan mode — there's no big secret to it. All it does is it adds one sentence to the prompt that's like "please don't code." That's all it is. You can actually just say that.

HOST: Yeah. So it sounds like a lot of the feature development for Claude Code is very much what we talk about at YC — talk to your users and then you come and implement it. It wasn't the other way that you had this master plan and then implemented all the features.

BORIS: Yeah. Yeah. I mean that's all it was. Plan mode was — we saw users that were like "hey Claude come up with an idea, plan this out but don't write any code yet." And there were various versions of this. Sometimes it was just talking through an idea. Sometimes it was these very sophisticated specs that they were asking Claude to write, but the common dimension was do a thing without coding yet. And so literally this was like Sunday night at 10 p.m. I was just looking at GitHub issues and kind of seeing what people were talking about and looking at our internal Slack feedback channel and I just wrote this thing in like 30 minutes and then shipped it that night. It went out Monday morning. That was plan mode.

HOST: So do you mean that there will be no need for plan mode in the sense of "I'm worried that the model's going to do the wrong thing or head off in the wrong direction" but there will still be a need for that — you need to think through the idea and figure out exactly what it is that you want and you have to do that somewhere.

BORIS: I kind of think about it in terms of increasing model capabilities. So maybe 6 months ago a plan was insufficient. So you get Claude to make a plan. Let's say even with plan mode you still have to kind of sit there and babysit because it can go off track. Nowadays what I do is probably 80% of my sessions I start in plan mode — I say plan mode has a limited lifespan but I'm a heavy plan mode user. Probably 80% of my sessions I start in plan mode and Claude will start making a plan. I'll move on to my second terminal tab and then I'll have it make another plan and then when I run out of tabs I open the desktop app and then I go to the code tab and then I just start a bunch of tabs there and they all start in plan mode probably 80% of the time. Once the plan is good, and sometimes it takes a little back and forth, I just get Claude to execute. And nowadays, what I find with Opus 4.5, I think it started with 4.6 it got really good. Once the plan is good, it just stays on track and it'll just do the thing exactly right almost every time.

And so before you had to babysit after the plan and before the plan, now it's just before the plan. So, maybe the next thing is you just won't have to babysit. You can just give a prompt and Claude will figure it out.

HOST: The next step is Claude just speaks to your users directly.

BORIS: Yeah, it just bypasses you entirely. It's funny. This is actually the current stuff for us. Our Claudes actually talk to each other. They talk to our users on Slack, at least internally pretty often. My Claude will tweet once in a while.

HOST: No way.

BORIS: But I actually delete it. It's just a little cheesy. I don't love the tone.

HOST: What does it want to tweet about?

BORIS: Sometimes it'll just respond to someone because I always have Cowork in the background and it's the Cowork that really loves to do that because it likes using a browser.

HOST: That's funny.

BORIS: A really common pattern is I ask Claude to build something. It'll look in the codebase. It'll see some engineer touched something in the git blame and then it'll message that engineer on Slack. Just asking a clarifying question and then once it gets an answer back, it'll keep going.

XII. Tips for Founders to Build for the Future

HOST: What are some tips for founders now on how to build for the future? Sounds like everything is really changing. What are some principles that will stay on and what will change?

BORIS: So I think some of these are pretty basic, but I think they're even more important now than they were before. So one example is latent demand. I mentioned it a thousand times. For me it's just the single biggest idea in product. It's a thing that no one understands. It's a thing I certainly did not understand my first few startups. And the idea is people will only do a thing that they already do. You can't get people to do a new thing. If people are trying to do a thing and you make it easier, that's a good idea. But if people are doing a thing and you try to make them do a different thing, they're not going to do that. And so you just have to make the thing that they're trying to do easier. And I think Claude is going to get increasingly good at figuring out these product ideas for you just because it can look at feedback, it can look at debug logs, it can kind of figure this out.

HOST: That's what you mean by plan mode was latent demand — that people were already like, I don't know, had their Claude chat window open in a browser and were talking to it to figure out the spec and what it should do. And now plan mode just became that — you just do it in Claude Code.

BORIS: Yeah. Yeah, that's it. Sometimes what I'll do is I'll just walk around the office on our floor and I'll just kind of stand behind people — I'll say hi so it's not creepy — and then I'll just see how they're using Claude Code. And this is also just something I saw a lot but it also came up in GitHub issues, like people were talking about it.

XIII. How Much Life Does the Terminal Still Have?

HOST: It seems like you're surprised how far the terminal has gone and how far it's been pushed. How far do you think it has left to go just given this world of swarm, multiple agents? Do you think there's going to be a need for a different UI on top of it?

BORIS: It's funny. If you asked me this a year ago I would have said the terminal has like a three-month lifespan and then we're going to move on to the next thing. And you can see us experimenting with this right because Claude Code started in a terminal but now it's on web, Claude Code is in the desktop app — we've had that for three months or six months or something just in the code tab. It's in the iOS and Android apps just in the code tab. It's in Slack. It's in GitHub. There's VS Code extensions. There's JetBrains extensions. So we're always experimenting with different form factors for this thing to figure out what's the next thing. I've been wrong so far about the lifespan of the CLI. So, I'm probably not the person to forecast that.

XIV. Advice for Dev Tool Founders

HOST: What about your advice to dev tool founders? Someone's building a dev tool company today. Should they be building for engineers and humans or should they be thinking more about what Claude is going to think and want and build for the agent?

BORIS: The way I would frame it is think about the thing that the model wants to do and figure out how do you make that easier. And that's something that we saw — when I first started hacking on Claude Code, I realized this thing just wants to use tools. It just wants to interact with the world. And how do you enable that? Well, the way you don't do it is you put it in a box and you're like, here's the API, here's how you interact with me, and here's how you interact with the world. The way you do it is you see what tools it wants to use. You see what it's trying to do, and you enable that the same way that you do for your users. And so if you're building a dev tool startup, I would think about what is the problem you want to solve for the user? And then when you apply the model to solving this problem, what is the thing the model wants to do? And then what is the technical and product solution that serves the latent demand of both?

XV. Claude Code and TypeScript Parallels

HOST: Back in the day, more than 10 years ago, you were a very heavy user and you wrote a book about TypeScript, right? Before TypeScript was cool. This is when everyone was deep in JavaScript. This is back in the early 2010s, right?

BORIS: Yeah, something like that. Before TypeScript was a thing because back then it was a very weird language. It's not supposed to do a lot of things with being typed in JavaScript and now it's the right thing and it feels like Claude Code in the terminal has a lot of parallels with TypeScript at the beginning.

HOST: TypeScript makes a lot of really weird language decisions. So if you look at the type system pretty much anything can be a literal type for example and this is super weird because even Haskell doesn't even do this. It's just too extreme. Or it has conditional types which I don't think any language thought of at all. It was very strongly typed.

BORIS: Yeah, it was very strongly typed and the idea was — when Joe Pamer and Anders and the early team was building this thing, the way they built it is okay, we have these teams with these big untyped JavaScript code bases. We have to get types in there, but we're not going to get engineers to change the way that they code. You're not going to get JavaScript people to have 15 layers of class inheritance like you would a Java programmer, right? They're going to write code the way they're going to write it. They're going to use reflection and they're going to use mutation and they're going to use all these features that traditionally are very very difficult to type.

HOST: They're very unsafe to type to any strong functional programmer.

BORIS: That's right. And so the thing that they did instead of getting people to change the way that they code, they built a type system around this. And it was just brilliant because there's all these ideas that no one was thinking about even in academia. No one thought of a bunch of these ideas. It purely came out of the practice of observing people and seeing how JavaScript programmers want to write code.

And so for Claude Code there are some ideas that are kind of similar in that you can use it like a Unix utility. You can pipe into it. You can pipe out of it. In some ways it is kind of rigorous in this way but in almost every other way it's just the tool that we wanted. I build a tool for myself and then the team builds the tool for themselves and then for Anthropic employees and then for users and it just ends up being really useful. It's not this principled and academic thing which I think the proof is actually in the results.

HOST: Now fast forward more than 15 years later not many codebases are in Haskell which is more academic and there's tons of them now on TypeScript because it's way more practical, right? Which is interesting.

BORIS: Yeah, it is interesting. It's like TypeScript solves a problem.

XVI. Designing for the Terminal Was Hard

HOST: I guess one thing that's cool — I don't know how many people know, but the terminal is actually one of the most beautiful terminal apps out there and is actually written with React terminal.

BORIS: When I first started building it, I did front-end engineering for a while. And I was also sort of a hybrid — I do design and user research and write code and all this stuff. And we love hiring engineers that are like this. We just love generalists. So for me it's like okay, I'm building a thing for the terminal. I'm actually kind of a shitty Vim user. So how do I build a thing for people like me that are going to be working in a terminal. And I think just the delight is so important. And I feel like at YC this is something you talk about a lot, right? It's build a thing that people love. If the product is useful but you don't fall in love with it, that's not great. So it kind of has to do both.

Designing for the terminal honestly has been hard, right? It's like 80 by 100 characters or whatever. You have 256 colors, you have one font size, you don't have mouse interactions, there's all this stuff you can't do, and there's all these very hard trade-offs. So, a little-known thing, for example, is you can actually enable mouse interactions in a terminal. So, you can enable clicking and stuff.

HOST: Oh, how do you do that in Claude Code? I've been trying to figure out how to do this.

BORIS: We don't have it in Claude Code because we actually prototyped it a few times and it felt really bad because the trade-off is you have to virtualize scrolling and there's all these weird trade-offs because the way terminals work is there's no DOM, right? It's like there's ANSI escape codes and these kind of weird organically evolved specs since the 1960s or whatever.

HOST: Yeah. It feels like BBSes. It's like a BBS door game.

BORIS: Oh my god. That's like a great compliment. It should feel like you're discovering Lord of the Red Dragon. It's fantastic.

But we've had to discover all these UX principles for building the terminal because no one really writes about this stuff. And if you look at the big terminal apps of the 80s or 90s or 2000s or whatever, they use ncurses and they have all these windows and things like this. And it just looks kind of janky by modern standards. It just looks too heavy and complicated. And so we had to reinvent a lot. And for example, something like the terminal spinner, the spinner words, it's gone through probably I want to say like 50 maybe 100 iterations at this point. And probably 80% of those didn't ship. So we tried it, it didn't feel good, move on to the next one. Try it, didn't feel good, move on to the next one.

And this was sort of one of the amazing things about Claude Code — you can write these prototypes and you can do like 20 prototypes back to back, see which one you like, and then ship that and the whole thing takes maybe a couple hours. Whereas in the past, what you would have had to do is use Origami or Framer or something like this. You built maybe three prototypes, it took two weeks. It just took much longer. And so we have this luxury of we have to discover this new thing. We have to build a thing. We don't know what the right endpoint is, but we can iterate there so quickly and that's what makes it really easy and that's what lets us build a product that's joyous and that people like to use.

XVII. Other Advice for Builders

HOST: Boris, you had other advice for builders and we kept interrupting you because we have so many questions. I would say —

BORIS: So okay, maybe two pieces of advice that are kind of weird because it's about building for the model. So one is don't build for the model of today, build for the model of 6 months from now. This is sort of weird, right? Because you can't find PMF if the product doesn't work. But actually this is the thing that you should do because otherwise what will happen is you spend a bunch of work, you find PMF for the product right now and then you're just going to get leapfrogged by someone else because they're building for the next model and a new model comes out every few months. Use the model, feel out the boundary of what it can do and then build for the model that you think will be the model maybe 6 months from now.

I think the second thing is — actually in the Claude Code area where we sit we have a framed copy of the bitter lesson on the wall. And this is Rich Sutton — everyone should read it if you haven't — and the idea is the more general model will always beat the more specific model and there's a lot of corollaries to this but essentially what it boils down to is never bet against the model. And so this is just a thing that we always think about where we could build a feature into Claude Code. We could make it better as a product and we call this scaffolding. That's all the code that's not the model itself. But we could also just wait a couple months and the model can probably just do the thing instead.

And there's always this trade-off. It's like engineering work now and you can extend the capability a little bit, maybe 10, 20% or whatever in whatever domain on the spider chart of what you're trying to extend. Or you can just wait and the next model will do it. So just always think in terms of this trade-off — where do you actually want to invest and assume that whatever the scaffolding is, it's just temporary.

HOST: How often do you rewrite the code base of Claude Code? Is it every six months? Is there scaffolding that you've deleted because you don't need it anymore because the model just improved?

BORIS: Oh so much. Yeah. All of Claude Code has just been written and rewritten and rewritten and rewritten over and over and over. We unship tools every couple weeks. We add new tools every couple weeks. There is no part of Claude Code that was around six months ago. It's just constantly rewritten.

HOST: Would you say most of the code base for current Claude Code — is only say 80% of it only less than a couple months old?

BORIS: Yeah, definitely. It might even be less. Maybe a couple months. That feels about right.

HOST: So the life cycle of code now. That's another alpha — expecting the shelf life to be just a couple months.

BORIS: Yeah. For the best founders.

XVIII. Productivity per Engineer

HOST: Do you see Steve Yegge's post about how awesome working at Anthropic is? And I think there's a line in there that says that an Anthropic engineer currently averages 1,000x more productivity than a Google engineer at Google's peak which is really an insane number honestly. Like 1,000x — three years ago we were still talking about 10x engineers. Now we're talking about 1,000x on top of a Google engineer in their prime. This is unbelievable honestly.

BORIS: Yeah, I mean internally if you look at technical employees, they all use Claude Code every day. And even non-technical employees — I think like half the sales team uses Claude Code. They've started switching to Cowork because it's a little easier to use. It has a VM, so it's a little bit safer. But yeah, we actually just pulled a stat and I think the team doubled in size last year, but productivity per engineer grew something like 70%. It's measured by just the simplest stupidest measure — pull requests. But we also cross-check that against commits and the lifetime of commits and things like this. And since Claude Code came out, productivity per engineer at Anthropic has grown 150%.

And this is crazy because in my old life I was responsible for code quality at Meta. I was responsible for the quality of all of our code bases across every product — Facebook, Instagram, WhatsApp, whatever. And one of the things that the team worked on was improving productivity. And back then seeing a gain of something like 2% in productivity — that was a year of work by hundreds of people. And so this 100%+ — this is just unheard of. Completely unheard of.

XIX. Why Boris Chose to Join Anthropic

HOST: What drove you to come over to Anthropic? I mean basically as a builder you could go anywhere. What was the moment that made you say this is the set of people or this is the approach?

BORIS: I was living in rural Japan and I was opening up Hacker News every morning and I was reading the news and it was all — it just started to be AI stuff at some point and I started to use some of these early products and I remember the first couple times that I used it I was just — it just took my breath away. That's very cheesy to say, but that was actually the feeling. It was just amazing. As a builder, I've just never kind of felt this feeling using these very early products. That was in the Claude 2 days or something like that.

And so I just started talking to friends at labs just to kind of see what was going on. And I met Ben Mann who's one of the founders at Anthropic and he just immediately won me over. And as soon as I met the rest of the team at Anthropic it just won me over and I think probably in two ways. So one is it operates as a research lab. The product was teeny teeny tiny. It's really all about building a safe model. That's all that matters. And so this idea of just being very close to the model and being very close to development and being not the most important thing because the product isn't anymore. It's just the model is the thing that's the most important. That really resonated with me after building product for many years.

And then the second thing was just how mission-driven it is. I'm a huge sci-fi reader. My bookshelf is just filled with sci-fi. And so I just know how bad this can go. And when I kind of think about what's going to happen this year, it's going to be totally insane. And in the worst case it can go very very bad. And so I just wanted to be at a place that really understood that and kind of really internalized that. And at Anthropic, if you overhear conversations in the lunchroom or in the hallway, people are talking about AI safety. This is really the thing that everyone cares about more than anything. And so I just wanted to be in a place like that. I know for me personally the mission is just so important.

XX. How Coding Will Change

HOST: What is going to happen this year?

BORIS: Okay. So if you think back like six months ago and kind of what are the predictions that people are making? So Dario predicted that 90% of the code at Anthropic would be written by Claude. This is true. For me personally it's been 100% since Opus 4.5. I uninstalled my IDE. I don't edit a single line of code by hand. It's just 100% Claude Code and Opus. And I land like 20 PRs a day every day. If you look at Anthropic overall it ranges between 70 to 90% depending on the team. For a lot of teams it's also 100%. For a lot of people it's 100%.

And I remember making this prediction back in May when we GA'd Claude Code that you wouldn't need an IDE to code anymore. And it was totally crazy to say. I feel like people in the audience gasped because it was such a silly prediction at the time. But really all it is is you just trace the exponential and this is just so deep in the DNA at Anthropic because three of our founders were co-authors of the scaling laws paper. They kind of saw this very early and so this is just tracing the exponential — this is what's going to happen and yes that happened.

So continuing to trace the exponential I think what will happen is coding will be generally solved for everyone. And I think today coding is practically solved for me and I think it'll be the case for everyone. Regardless of domain, I think we're going to start to see the title software engineer go away. And I think it's just going to be maybe builder, maybe product manager, maybe we'll keep the title as kind of a vestigial thing, but the work that people do, it's not just going to be coding. Software engineers are also going to be writing specs. They're going to be talking to users. This thing that we're starting to see right now in our team where engineers are very much generalists and every single function on our team codes — our PMs code, our designers code, our EM codes, our finance guy codes, everyone on our team codes. We're going to start to see this everywhere.

So this is sort of the lower bound if we just continue the trend. The upper bound I think is a lot scarier. And this is something like we hit ASL-4. At Anthropic, we talk about these safety levels. ASL-3 is where the models are right now. ASL-4 is the model is recursively self-improving. And so if this happens, essentially, we have to meet a bunch of criteria before we can release a model. And so the extreme is that this happens or there's some kind of catastrophic misuse like people are using the model to design bioviruses, design zero-days, stuff like this. And this is something that we're really really actively working on so that doesn't happen.

I think it's just been honestly so exciting and humbling seeing how people are using Claude Code. I just wanted to build a cool thing and it ended up being really useful and that was so surprising and so exciting.

XXI. Outro

HOST: My impression from Twitter or just the outside is basically everyone went away over the holidays and then found out about Claude Code and it's just been crazy ever since. Is that how it was for you internally? Were you having a nice Christmas break and then came back and like what happened?

BORIS: Well, actually for all of December, I was traveling around. And I took a coding vacation. So, we were kind of traveling around and I was just coding every day. So, that was really nice. And then I also started to use Twitter at the time because I worked on Threads back then, way back when. So, I've been a Threads user for a while. So, I just tried to see other platforms where people are. Yeah. I think for a lot of people they kind of discovered — that was the moment where they discovered Opus 4.5. I kind of already knew. And internally Claude Code's just been on this exponential tear for many many months now. So that just became even more steep. That's what we saw.

And if you look at Claude Code now, there was some stat from Mercury that 70% of startups are choosing Claude as their model of choice. There was some other stat from Semi Analysis that 4% of all public commits are made by Claude Code — of all code written everywhere. All the companies use Claude Code from the biggest companies to the smallest startups. It wrote — it plotted the course for Perseverance, the Mars rover. This is just the coolest thing for me. And we even printed posters because the team was like, "Wow, this is just so cool that NASA chooses to use this thing." So, yeah, it's just humbling. But it also feels like the very beginning.

HOST: What's the interaction between Claude Code and then Cowork? Was it a fork of Claude Code? Was it like you had Claude Code look at the Claude Code and say let's make a new spec for non-technical people that keeps all the lessons and then it went off for a couple days and did that? What's the genesis of that and where do you think that goes?

BORIS: This is going to be like my fifth time using the word latent demand. It was just that. We were looking at Twitter and there was that one guy that was using Claude Code to monitor his tomato plants. There was this other person that was using it to recover wedding photos off of a corrupted hard drive. There were people using it for finance. When we looked internally at Anthropic, every designer is using it. The entire finance team at this point is using it. The entire data science team is using it — not for coding. People are jumping over hoops to install a thing in the terminal so that they could use this. So we knew for a while that we wanted to build something and so we were experimenting with a bunch of different ideas and the thing that took off was just a little Claude Code wrapper in a GUI in the desktop app and that's all it is. It's just Claude Code under the hood. It's the same agent.

HOST: Oh wow.

BORIS: And Felix and the team — Felix was an early Electron contributor. He kind of knows that stack really well and he was hacking on various ideas and they built it in I think something like 10 days. It was just 100% written by Claude Code. And it just felt ready to release. There was a lot of stuff that we had to build for non-technical users. So it's a little bit different than a technical audience. It runs in a — all the code runs in a virtual machine. There's a lot of deletion protections and things like this. There's a lot of permission prompting and other guardrails for users. Yeah, it was honestly pretty obvious.

HOST: Boris, thank you so much for making something that is taking away all my sleep, but in return, it's making me feel creator mode again, sort of founder mode again. It's been an exhilarating 3 weeks. I can't believe I waited that long since November to actually get into it. Thank you so much for being with us. Thank you for building what you're building.

BORIS: Yeah, thanks for having me. And send bugs.

HOST: Sounds good.

Transcript source: "The Lightcone" (Y Combinator) — Inside Claude Code With Its Creator Boris Cherny. YouTube. Formatted for readability.

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2.20.2026