# The Future of Claude Code: Mods, Mutable Software, & Multiplayer Agents — Thariq Shihipar, Anthropic Latent Space · 2026-09-29 · 92 min · https://www.youtube.com/watch?v=IZAlq-V19U8 ## Transcript swyx I think different models are very different from each other. But I realize that it's such a pain to maintain different ones. As the models get better and better, the floor of how they accomplish simpler tasks gets better. So I do think that, in the limit, CLAUDE.md goes away—and maybe not even that far. I think that right now it might be better to start a new project without a CLAUDE.md. Thariq Shihipar I think that if you see very repeated failure modes, you add them to your CLAUDE.md. The really tough thing is that this changes per model. You need CLAUDE.md, you need Opus.md. Even Fable 5.1 versus Fable 5 is annoying. We don't do this on purpose; it's just how the models work. Maybe Claude 4 had a failure mode that Claude 4.1 doesn't, and if you keep this running log of a bunch of different failure modes, they will probably over-constrain Claude. We actually just added eval plugins for skills, so now you can evaluate whether a skill is better. swyx ### Introduction We're here in the studio with our friend Thariq from Anthropic. Generally, with Claude Code, there's so much merging of boundaries, and you've been so on top of everything since you joined Anthropic. You were early to Claude Code itself, but you've also told that story on other podcasts, and you've also been talking about thinking like an agent. ### Claude Tag as an Organizational Harness Most recently, you did the top AI Engineer talk, “Field Guide to Claude Code,” which obviously you guys launched Claude, so that's cheating. Most recently, you're also launching cloud tag, and we're going to be talking about pacing on the frontier. There's a lot going on at Anthropic. I guess the top-of-the-question is: what's it like being at Anthropic when there's so much going on? Thariq Shihipar I think you can get whiplash sometimes. When I joined Anthropic, I joined because of Claude Code. Claude Code had just come out, and Opus 4, to me, was so good that I could not imagine how good it was. That was a real moment for me. I was trying to convince my startup friends to use it for coding, and they were like, “Our engineers don't think it's good enough.” I was like, “That's insane.” Fast-forward 12 months, or less, and it's just the default way that everyone codes. Having to go from selling it to now teaching people how to make the most use of it and be more efficient is a big change. It's just hard to stay on top of everything as a human. Things happen so fast— swyx More agents at a time? Thariq Shihipar I mean, yeah. The agentic stuff scales much better than the human stuff. With humans, it's like, “There are 3 things happening right now, and they're all emergencies. How do you respond to them?” swyx What do you split your time on? You do a lot of technical writing and engineering work. Thariq Shihipar When I joined the Claude Code team, I wanted to teach people how to use Claude Code. I thought maybe I would spend a little bit of time on it. I was spending some time on the Agent SDK first, and I wasn't exactly sure how the bitter lesson would go when it came to harnesses. Sometimes we were like, “What's after Claude Code?” Initially, I just wanted to teach people how to use Claude Code and make it easier to use. As harnesses have gotten better and better, that's become the dominant problem: how do you use the agents? It's such a high-skill-expression thing. I do that, and then I do engineering work and give talks. When I'm doing engineering work, my goal is to take the feedback that we get from users and then be able to talk about how to use Claude Code for engineering. There's a good loop there. swyx For listeners, we'll attach the talk that you did with Sarah for the Dev Writers meetup, where we talked a little bit about “first you do the work, and then you talk about the work,” something like that. Sow and reap, or what was that? Thariq Shihipar Reap and sow and reap. swyx Something like that. And then, just to preview a little bit, we are going to talk about the evolution of the harness. It has come a long way from just being a CLI. We're going to talk about Claude mods, which is starting to leak today because you couldn't keep it secret. Thariq Shihipar Yeah, basically. swyx There's a lot there. I think you started off with adding the AskUserQuestion tool, which people would love and hate. I actually thought it was very innovative, and now I have my own version. You have your “Interview Me” version. ### Ask User Question and the Future of Agent Interfaces Thariq Shihipar Yeah. Everyone has their own stuff, and it no longer matters because now you're supposed to write prompts that create other prompts, loops, and all these things. What's the state of the art today? What are you telling people to do? swyx Sure. Thariq Shihipar AskUserQuestion was the first time that the model was good at elicitation. I have a human-computer-interaction background; I studied that in undergrad and graduate school. To me, this was human-agent interaction: trying to figure out how the agent can communicate with you and extract the requirements. ### Prompting as the Core Claude Code Skill One of the things that's difficult as Claude Code has gone broader and broader is that everyone has their own way of using it, and it's very hard to change the default behavior. For example, if someone asks Claude Code to do something, sometimes they just want it to do the work because they're a very good prompter. Sometimes they're not good at prompting, and the agent needs to clarify. AskUserQuestion sort of splits along that axis. Are you good enough to instruct the agent as it is, or does the agent need to pull out more requirements, collaborate with you, and really understand your preferences? On the whole, I believe that pretty much everyone is more on the latter side than the former. Everyone has more ambiguity, and they know less than they think they know about the problem. It's an interface-design problem to make that easy. If you're designing a problem or going through a problem, things like the schema and the call stack are really important. The details in the design are important. Ideally, you want to figure out some of these hard problems ahead of time before starting implementation. That's what they call unknowns, and I think this will forever be a skill in agentic coding: figuring out your unknowns. Even if the model is superintelligent, it needs to know what you want. You have preferences, and you need to pull those out. That's what I'm pushing. The question then is: how does the agent interact with you? HTML has been the big way of doing that. We've recently added artifacts, and I think we've done a bad job—or I've done a bad job—of explaining how to use them fully. We have a lot of powerful capabilities. Every artifact can have a database associated with it, so it can store and write persistent data. Artifacts can feed back into Claude. One thing that people aren't doing yet, which I'm trying to encourage, is this idea of a dashboard artifact. You have Claude working on a project long-term. Maybe it's like a Kanban or something. It can store that Kanban data in a database. Multiple Claudes can access that data via the Artifact MCP, and that artifact can talk to those Claudes as well. We're basically building the primitives for you to have this generative interface via artifacts that will let you surface more of that rich detail from the agents. I think that almost everything with agents right now is this problem of you think you know what you want, but you don't really know what you want. The agents need a lot of detail, and collaborating with them in the loop is really important. Artifacts are the way that we're trying to evolve there. But there's a lot of work to do because it's so much more complicated than a multiple-choice question. There's a lot more detail in terms of diagrams, code snippets, schemas, or whatever it is for that problem. Artifacts are the more AGI-pilled way of doing asks, basically. swyx ### Artifacts, Projects, and Multiplayer Agents I think one thing that's unclear to me about the artifact stuff is what feedback should go in through the artifact and what feedback should go through a Claude chat, because the more AGI-pilled one is to just feed everything to Claude. Thariq Shihipar I think the more AGI-pilled one is to go through the artifact. I think that, in the limit, we sort of imagine that artifacts will be your interface into the harness. You can comment on this live document of your plan or the work, and you can see maybe multiple agents, with different agents doing this and that. That artifact is built for the current work that you're doing, right? Each one has slightly different—We're still getting there from an infrastructure perspective, but I think an on-the-fly interface for your harness is probably where things are headed. swyx Is there a version of it that's an abstraction from CLI or chat? Because right now, a lot of it is: okay, you're interfacing with Claude Code, you're having HTML given back for a mockup, and it's pretty rich. There are diagrams, artifacts, and ways to connect these together. Why not just do everything that way? Then it becomes about separating out where the inference is happening, where the intelligence is happening, and where the work is happening. Thariq Shihipar I think this is kind of the difference between—or some of the distinction between—local and cloud, right? Right now, if you use Claude Code, it's local, and you can spin off Remote Control, for example, to get some cloud behavior, or you can spin off Claude Code in the cloud. We're moving toward a place where, instead of messaging a local Claude that starts a session locally and executes, you have a Claude that you message that's in the cloud and running. It can run local or cloud sessions. This is kind of how Claude Code works, but over time we'll add local hands as well. Local hands will be the ability for that agent to access your computer if it's online and be able to work there. It can spin off many different subagents, and those subagents can communicate with each other. That's where the artifact comes in, to display all of that work, basically. You can imagine you're separating out these things: there's the surface UI display, which is an artifact hosted somewhere and has a database and everything; there's the inference and intelligence happening in the cloud, and you don't have to worry about shutting off your computer; and then there are the hands. They can be local, in a remote sandbox, or wherever you need your work to be done. That's unpackaging the Claude Code experience. Right now, it all happens in one place. swyx How do you see the multiplayer side of that? Say teams want to work in this way. Right now it's very individual, but how do you see the future of multiplayer? Thariq Shihipar Right now, I guess there's Claude Code, which is a version, but we're launching Projects, and Projects is the abstraction that's kind of like Claude Code but on our cloud products. You can message it, and it will do the Claude Code stuff, like spinning off subagents. We think that, with multiplayer, Claude Code is a little bit more natively multiplayer because it's just in your Slack and the permissions are all figured out and stuff like that. But I do think multiplayer is an important part of the story, and that will need to get tied together more. You can imagine how complicated it gets when you're like, “Oh, you have hands, but now you have other hands in other people's computers too, and you need to permission them,” or you have your MCP and someone else's MCP, and how do you figure out how to use them? It gets quite complicated, and Claude Code does a good job of sanding down all of these issues. So, with Google Docs, how does it access Google Docs? It accesses it through the shared Claude MCP, or it can access it through your local credentials as well if it doesn't have access. I think Claude Code is our multiplayer product, and it's really useful for things that are inherently multiplayer. On-call incidents, for example, are inherently multiplayer. You want to tag Claude, you want multiple people to log in, and you want to be able to find context. Whenever I'm working on something and I want privacy or security, or I want other people to review it, it's really nice to have a channel per project. I'll tag Legal, for example, and say, “Hey, I want to ship this. Can you—here's everything Claude knows. Just chat with it.” That way, Legal gets precise answers on exactly what is shipping into the code, and I don't need to be in the loop. I think multiplayer is getting more and more to the point where everyone can participate with Claude. I think Claude Code is that product, and Projects will start off single-player and expand. swyx I think there's a question—or maybe dual questions—about identity and the unit of isolation. Claude Code, you specifically chose to make it its own identity, which is a controversial choice. There are other ways to do it. Claude Projects, probably—it sounds like, if it's anything like ChatGPT Projects, the isolation is that artifact, that Claude instance that everyone's collaborating on. It sounds like it should be—if you're collaborating with Legal on the thing, that channel should be a project, right? It's not yet, but that's the natural next step. Thariq Shihipar Yeah. I mean, in Claude Code, it's effectively—you have to sort of do your own arrangement, basically. In Claude Code, each channel is—you can name it as you want. I name each— swyx Feature, basically, as a channel. Thariq Shihipar But I think there's some transference—it's unclear when there is transference. Let's say you have a coworker— swyx Who is tagged on all these things. Thariq Shihipar Yes, there is transfer because it's the same person, but with Claude it's unclear if it's necessarily—well, no, you don't know anything about the other stuff. You should only use this stuff. swyx It's like the tip of the iceberg meme, right? Thariq Shihipar This is what we spend so much time on, basically. There's infinite surface area: you want Claude to—well, not infinite, but there's a lot of surface area to figure out in terms of permissions and visibility, and how you can let Claude operate as well and as safely as you can. Obviously, this is very important to us because security for our codebase is very, very important, and we've put a lot of time into this. There are so many edge cases you can figure out where it's like, “Oh, this Claude in this channel has different permissions, but it can message another channel. Can't it exfiltrate data that way?” Or, “What if it uses your MCP and then messages someone else?” There's so much to figure out, and we've really put a lot of work into sanding it down. swyx Yeah. Yeah. Lots of work. Okay. Vibhu, you wrote 2 good articles. I mean, you've written many good articles, but on, you know, a field guide to Fable, building cloud code. I'm curious: from what you've seen, are there any common patterns that you see in top users at Anthropic and externally? What are the best practices for getting the most out of Claude Code? Vibhu The meta-skill, I'd say, is that prompting is very important. I think this is not trivial to say because a lot of people are like, “Oh, prompting doesn't matter. I can just say a sentence and Claude will do it.” I think prompting is really like public speaking, or writing or something, for a specific audience. That audience is Claude, and you need to build a mental model of Claude and how it thinks and how it works. That's the most important skill in working with Claude Code: having this mental model of Claude and what it can do well, what it can one-shot, and what it can't. So many people, when you see their prompting, have short prompts, but they have such a good mental model of Claude, the codebase, and things like that that it's effortless. But it's a high skill ceiling. Thariq Shihipar So, that work of spending a lot of time prompting and building mental models—building an intuition for how the agents work—is really important. The next thing is the unknown stuff we talked about earlier: being able to find what you don't know or what you haven't written down. I think as Claude can do more and more things, the likelihood of you doing something out of distribution for you, where you have low domain knowledge, is very high. The more you can learn the vocabulary to be able to prompt Claude, the more important it becomes. I think the most important unknowns are the unknown unknowns, where you're like, “I just don't even know that this exists,” right? Vibhu Yeah, exactly. I think this is an illustration of the map and the territory. You're like, “Okay, this is my prompt,” and the territory is the actual work that the agent needs to do. If you are very precise, you can give more precise instructions. For example, in design, I'm not very precise. I'm not a designer, so I say, “Give me 8 different mockups.” But if I were a designer, maybe I'd say, “Here's some reference sites. I want this type of font and this type of look to it. Here are a few different components to visualize. Here's a Figma MC board to bring in.” You can be so much more precise with that language. If you're not a designer, you need to try to learn the language, basically, or learn the unknown unknowns. I think this is true of everything. The more you can work with Claude to learn how things work, the better your prompting will be. Another good example of this is game design. A lot of people are like, “I can vibe-code a game now,” and then they're like, “It's not fun.” The thing about game design is that every one of these choices has a lot of variations and a lot of craft to it. When you're making a flying game, the feel of the plane and the way it responds to your controls have a lot of craft to them. A game designer would spend days on that. swyx To me, that's what taste is, right? From the possible space of 1,000 mathematically valid answers, here's the one that humans will like. Thariq Shihipar Yes, I think with taste, I'm torn on this word because I think you're right, but everyone has different definitions. It sounds kind of low-skill or elitist, almost, where you're like, “There are certain people with taste.” swyx Taste is what I call taste. These guys don't have taste. Thariq Shihipar Yeah, exactly. “An engineer doesn't have taste; I, the founder, have taste.” I think that's actually not true. I think engineers have a lot of taste for these particular problems, and everyone has taste for particular problems. Jason Liu says that in order to have taste, you have to eat. I really like that. You have to do a lot of things, iterate, figure out what you want and what you like, and build that domain vocabulary. Then, when you're prompting, you're synthesizing all of that for— Vibhu Isn't it annoying when someone else says it better than you? I have to quote this guy forever. swyx Having to quote Jason Liu forever. He's going to love this. Vibhu So, I get props. Sometimes it's not even that. Sometimes it's just intuitive, right? You don't realize you even want something until a model puts it out and you're like, “This just feels immediately better,” right? swyx Yeah. Yeah. Exactly. Vibhu One thing I go back and forth on is the way I prompt half the time. Let's say I use voice. You guys have voice; other people have voice. I'll ramble for 2 minutes, press down the function key, let go, and hope it figures out what I mean. A lot of the time, it does. swyx But it's not as thoughtful as a structured prompt with well-written communication, as though it's a PRD or a memo. Vibhu Is that in line with how people do this? There's basically bimodal prompting, where there are some prompts where you spend a lot of time up front, and other prompts you just dash off. Thariq Shihipar I don't think voice is necessarily lower quality. I think it's more about how much information is in the prompt. You can add some “um”s and “uh”s and extra sentences and be like, “Actually, I changed my mind in the middle of the prompt,” and the model will be able to follow that perfectly. The actual format of the text is less important than how much information is in it. For voice, going back to human-AI interaction, it's just much easier for a lot of people to talk than to type. If that gets more information out of you, that's better. Vibhu At some level, it feels like giving the model as much context as possible before you kick off is a best practice. I don't know. A lot of the time, when I was first trying out Claude Code, I spent a solid 30 minutes really crafting a long prompt. I think this is a response to models running for longer and longer. It's still a little difficult to nudge them while they're in the loop, but I intuitively spend more time crafting that first prompt and working with it a lot. ### Context, Effort, and Smarter Model Usage Thariq Shihipar My personal opinion is that if I were a software engineer—if I were running my own startup, for example—I think I would mostly stick to a Max 20x. Verification and code review might be separate things, but what I see a lot of the time is people hit rate limits when they're doing this sort of thing. The model does a lot of work, and then you're like, “I don't like this. Can you undo this and redo it?” Then you're iterating on something the model could have done if you had spent more time up front or given it better context. Instead, you're like, “Nope, I don't like that design. Try this,” or, “You messed this up.” That eats up so much more of your usage. That's a key tip for efficiency as well. Context isn't just about what the goal is. Are you building a prototype, or is it a production thing? Where can you spend compute, and where can you not spend compute? You have to give the model permission—or not permission—to do things sometimes, because it doesn't intuitively know how much you want to spend on a task. You can use effort for this. I'm working on a blog post about that. We see that effort scales with the complexity of the task. For security, effort gets much better results: high effort versus low effort changes the eval. For software engineering, it doesn't change things by a huge amount, because effort is mostly spent on verification, edge-case testing, and things like that. Being able to give the model that guidance—“This problem is something that I want you to spend a lot of time verifying and edge-case testing”—is important. Vibhu How about models in the mix? There's Opus and Fable with effort. There's also Haiku in there. Thariq Shihipar Yeah. It's not quite true yet, but it's very close. I think the frontier models will be Pareto-dominant over almost everything. Sometimes I think Opus might be Pareto-dominant, depending on how things shake out and whether it's a newer version of Opus. Increasingly, the smart model is going to be able to do a simple task for fewer tokens than the other models, basically because of verification. With verification, in the limit, your model doesn't need to verify, right? If it's a perfect model, it just does the work once and it's like, “Okay, I did it.” Increasingly, with Fable, I'm like, “You don't need to spin up Chromium and screenshot all of these things. I see it. You did it, right?” At higher effort, you spend more of those tokens verifying. But if you're working on simpler problems—and a lot of software engineering is simpler—then in Claude Code, at low and medium effort, it can spend fewer tokens verifying. As the models get smarter and smarter, they'll just be able to say, “All right, done.” I can run the linter for sanity's sake, but I know it lints. You don't even need to do that. That will be so much more token-efficient than the smaller models, basically. swyx Is there a good practice on our side that we can use to see if we're using too much effort? I hate wasting time on that kind of stuff. Thariq Shihipar Yeah, I know what you mean. In this blog post, my rough distribution is that code review and security should be high or max, basically, and software engineering should be set per domain. Yeah. I think if you're doing UI or something like that, low and medium are fine. If you're building an API and want to make sure you cover enough edge cases, you need higher effort. Building that mental model of how things work across these distributions is part of the job. swyx Is this more intuition-driven or eval-driven? I'm guessing this would change as well. Vibhu He has evals. Thariq Shihipar Yeah. So what I did in the blog post is go over all the Terminal-Bench evals. There are about 70 problems, and I'm showing that in the security problems, it does more. I also look at some of the transcripts, in terms of what it answers and what it forgets. A lot of times, this is another prompting tip I have: ask it to make decision notes or implementation notes. In basically every eval problem it faces, it thinks about the correct solution and decides not to do it. It's like, “Here's the answer. What if I did this?” And then it's like, “Probably not,” and keeps going. This is the majority of the failures. At a higher or max level, it's very rare that the model just doesn't know how to do something. If you have these implementation notes, you can review them and say, “Actually, I want you to do this thing that you didn't do.” The models are getting better at surfacing that overall. I see in the transcripts that Fable 5.1, when it produces this output, will call out its decision-making as well, but making this more explicit in the harness is better. Now we're allowing ways for you to modify the harness, so you can add some help there. swyx Yeah. I want to call out 2 things that you mentioned that I think actually exist outside of prompting. One is—let's call it—the prompt that's so important that it shouldn't be in a prompt. It's actually in CLAUDE.md or AGENTS.md. That's goals: your situation, your goals, the things that you want. And the second is the decision log, the experiment log, or whatever log of traces you might want to survive the current session to do those things. Those are externalities. There's no standard; it's not like skills, and it's not like MCP. It's just a Markdown file. ### Is Claude.md Going Away? First of all, is that right? Is CLAUDE.md going away? You have a documented dislike of AGENTS.md, but you're going to do it. Thariq Shihipar Yeah. Okay. So, I mean, AGENTS.md—we're going to do it. I think different models are very different from each other, but I realize it's such a pain to maintain different ones. As the models get better and better, the floor of how they accomplish simpler tasks is better. I do think, in the limit, CLAUDE.md goes away, and maybe not even that far. I think— swyx I think right now it might be better to start a new project without a CLAUDE.md. Thariq Shihipar Yes. swyx I think maybe if you see very repeated failure modes, you add them to your CLAUDE.md. The really tough thing is that this changes per model. So if you've added a bunch of failure modes—or even— Thariq Shihipar You need CLAUDE.md, you need Opus.md. Well, even Claude 4.5 versus Claude 4 is annoying. We don't do this on purpose; it's just how the models work. Maybe Claude 4 had this failure mode that Claude 4.5 doesn't. If you keep this context, this running log of a bunch of different failure modes, they will probably overconstrain Claude. We just added eval plugins for skills, so now you can evaluate whether a skill is better. I think Daisy on our team did this. We're trying to work on this. You still have to spend tokens on it, and it's not perfect, but we're trying to help with this problem. As far as prompting goes, the one tip I want to offer is: sufficiently advanced prompting is indistinguishable from sufficiently advanced executive communication. I've referred to this as the Executive Comms workshop from Heavybit. It's the best I've ever seen in my career, and they teach something called the SCQA model. Just Google it. It's a thing; people have been doing prompting for decades. It's just called executive communications. It's when one person has to communicate to thousands of people down the org chart. This is what you do: situation, complication, question, and answer. It's how you write the memo. Obviously, sometimes you don't have the answer, but you can at least list out the situation, complication, and question. They have some examples in there, so I'm just leaving breadcrumbs for people if they want to explore. swyx Before we move on, I want to ask you: any other underrated tips or ways people could get a lot of value from Claude Code that they're not using? Thariq Shihipar Yeah, a lot of them are in the Unknowns doc. I give a bunch of example prompts, like using it for brainstorming and using it to quiz you afterward. We added this Explain Like I'm 5 skill, which is a very short prompt. It doesn't even say “Explain Like I'm 5”; the key phrase is basically “big picture in a few words.” That's the main thing, and it's shockingly good. I think I tweeted about this. It's `/eli5`, and you can install it as a plugin, but it's way better at cutting through the BS and being like, “Yeah, exactly right here.” The diagrams are quite clear. One thing that's true with artifacts is that they put too much text in, and people aren't reading the artifacts. This simplifies it a lot more. This came out of people at Anthropic going through very complicated incidents and saying, “What is happening?” This one is great. swyx My version of this is the “test your understanding” one. It gives you a few choices, and if you get it wrong, there's a mismatch between what you think is happening and what's actually happening. Thariq Shihipar Yeah. I think this is one of those things everyone loves talking about and very few people really do. Most people just don't want to get quizzed about something. Unfortunately, I think this is one of the things that we need to— swyx What's the opposite of asking you a question? Ask the question before the thing. This is after the thing. Thariq Shihipar Exactly. It's a good way to stay grounded: do you even know what you're doing? The worst case is when people send you slop and haven't understood what they're asking for or what the output is. It's like, “Dude, I don't want to read this. Do you even know what it is?” So you make it a rule for yourself that before you send stuff, you should at least know what's implemented. swyx Yes. You could make this a mod, and you could build your own mod to make sure you test it. We can talk about that. Let's get right into it. What is a Claude Code mod, and what is this diagram showing? Thariq Shihipar Yeah. Claude Code mods basically let you customize the entire Claude Code harness. If you have requests, let us know; we'll add more and more. This works for a CLI, it works for desktop, and maybe it will work for Claude Code in the future. We're trying to make this very extensible. You can see this reference sheet. I don't want people to get overwhelmed by it. At a high level, you can customize both the execution of the harness and the UI of the harness. In that Tetris example from Boris, that's customizing the UI—showing Tetris in the game. Let's say you wanted to test your assumptions or test your understanding after every project. You would ask Claude to make this plugin. It would spin up a classifier after every prompt, basically. At the end of each turn, you would spin off a subagent, or a forked agent. A forked agent maintains the prompt cache. That's one of those unintuitive things: you can fork and make a little request, and it'll be very cheap because the entire prompt cache is done. You can ask, “Has this task been completed?” swyx This is how you do `/btw` and all those. Thariq Shihipar Yeah. The underlying forked agent, yes. In the forked subagent, you can say, “Has this task been completed?” If so, return true. Then in your hook—or in your plugin mod, sorry, in the subagent—you would say, “If true, give me a quiz,” and have it return questions and answers in a JSON format. You'd parse it, and then display this list of questions above the prompt input. This is slightly token-intensive because you have to do it after every end of the assistant turn, but it's a lightweight classification. Then you can get this quiz, and Claude will always do it for you. You don't need to remember to do it. There are lots of these tips that we've talked about, where it's like, “Oh, implementation notes.” You can also add a tool for implementation notes now. The tool that I'm adding is called, I think, “register assumption,” although maybe I'll change it around. This is a mod: you give it a register-assumption tool, and it will keep a list. Every time it does something, it'll add to the list, and at the end it'll display those assumptions. Another mod I'm working on is a model router—internal Claude model routing. The reason we don't do model routing by default is that it's a hard problem. You know what I mean? swyx You will get it wrong. Thariq Shihipar Yeah, you will accidentally use Fable for a hard problem or Sonnet for swyx You have auto-approve, but you don't have auto mode. Thariq Shihipar Well, you will have auto mode; you just don't have auto routing or something. swyx Auto mode for model picker. Thariq Shihipar Yeah, exactly, exactly. So— swyx I'm getting at the rough question of how much you open this up and how much people have to think about this. When you talk about prompt caching and building a router, it seems like you could easily build a mod that routes per query, and I'm just killing my plan very fast, right? I guess my question is more: what does a product doc like this look like? Who is it for? Is it for power users? Is it for everyone? Should everyone be able to— ### Model Routing and the Rise of Mutable Software Vibhu Definitely power users, right? Thariq Shihipar Yeah. I mean, I think it is power users, but the nature of Claude Code is that so many people are power users, because it's easy to share things. One person can make a good model-router thing that doesn't break prompt caching all the time, and then you can compose them. Another cool thing about plugins is that they can hook into and compose with each other. I have a mod that will create a mode selector at the top, and any plugins can register to be a mode. The auto router can be a mode, right? Or you can have a mode that's artifact mode, where it primarily talks to you in artifacts. It's kind of like toggling between plan mode, you know what I mean? You can create more and more of these modes, but the ability to create modes is itself a mod. There's a lot of richness here, but we do want to make it fairly easy. We want to make it so that you can just install someone else's, and you can chat with Claude. We'll make sure that it understands nuances like prompt caching, so it can warn you. This isn't extremely complicated behavior for Claude, I think, but we should have a good skill on how to make mods. We'll see how we go. But I do think that this is a preview of mutable software, and how generative software can be customized safely. If enabled, you could customize any piece of software. I think more and more apps should ideally do something like this. Vibhu And by the way, you have another cool tweet about how there's the infinite money button, which is making your SaaS consumable by agents. I think mutable software is interesting, and other people have also tried to do it. I think the hurdle comes when you can do everything, and then users tend to get confused. Usually, what works is just 1 opinionated flow. This is on the side of less opinionation: more power to power users, and I think it's probably unlocked by AI, where you can just prompt for whatever the thing is. swyx Yeah. Or there can be a skill that gives the opinions, and then— Vibhu So, knowing a little bit about TypeScript and build systems and all these things, I'm actually very curious about the team who worked on this. I don't know how close you were to them or whether they drew any inspiration from build systems like Babel and Webpack, all these old-school things, because it sounds very similar: the plugin ecosystem, where things can compose with each other. Thariq Shihipar Yeah, I'm not deep in the technical details, but I do know it was a collaboration between someone on the Bun team and someone on the Claude Code team. Vibhu Build system. Thariq Shihipar Yeah, exactly. It's very exciting. Agents can do this very complicated sort of extensibility in your software now. Another reason, if you run a startup, is that you can prompt Claude and be like, “Hey, could we make an extension system? What would that look like?” Vibhu Yeah. Yeah. swyx And I just really wonder—you had hooks in the past— Vibhu And plugins, all these things. So what specifically will mods be able to do that those things could not do? Thariq Shihipar Internally, we were originally calling this function hooks. That gives you a little bit of an idea: hooks register an event to happen and then a script to call, basically. Inside the TypeScript runtime, things are running, so you get the benefits of having a bunch of things in scope—for example, how many turns are in this conversation, how many tokens have been used, what the messages are, things like that. It has a bunch of information that can be used, and there are a lot more hooks—more fun things you can register for. Because it's all happening in-process, you can spawn subagents with forked context and stuff; that will return, you can parse the results, and you can use structured output to return them. You can modify the UI, which you could never do in hooks. swyx Yeah. So, modify UI—this is why you show the Tetris example. Does it also extend to artifacts? I assume it does. Thariq Shihipar Artifacts are kind of a different way of customizing it. One of the mods I'm working on is a dashboard mod, which will prompt Claude to maintain a dashboard that's an artifact. They're kind of slightly orthogonal—or not orthogonal. They compose with each other in different ways. Mods are a little more like they're in your Claude Code harness, changing the agent loop, and the UI is an added benefit. Artifacts are for when you want to see things at a high level, very interactively; the affordances can be a lot bigger than a TUI or even in our desktop. swyx I'm guessing you'll have a good blog post on the differences, because right now you can also make a loop that outputs to an artifact that's an interactive dashboard, but you can also do it with a mod. There's just some thinking about hacking on a harness when we don't know much about the harness, right? Thariq Shihipar Well, something I'm excited about with mods is that there are so many things for Claude Code that you just have to remember. You're like, “Oh, let me do this, and then let me call the dashboard skill that does the loop,” or, “Let me test my assumptions afterward.” If you do all of these things using little classifiers and stuff, and you're like, “These are the things I care about. This is what I want to do,” you don't have to remember as much. One more mod I'm working on is a next-steps mod that— Vibhu I have a next-step skill. I always run next steps. Does it have access to your skills? This is one of those things where I'm like— Thariq Shihipar I think so. Vibhu Okay, yeah. swyx Does it need specific access to it? It always has— Thariq Shihipar I think there's specific prompting, I guess, to know your skills. Claude forgets them sometimes throughout the thing. But anyway, the idea is that next steps can also say, “Oh, hey, this has happened. Use the explain skill to explain what happened,” because this seems quite complex. Or, “Use your unknown skill.” It looks like you're asking the model to iterate on these small changes. It seems like you could prompt better: what if you did this? So I think spending more compute there— Vibhu Yeah, yeah, yeah. And it should always come out as multiple choice. I have my next-step skill—it's like this. swyx Okay, perfect. Yeah, you can steal. Vibhu Yeah, yeah, yeah. Thariq Shihipar For me, models really always need to be reminded: what are you trying to do here? swyx Yeah. Thariq Shihipar Look at the whole transcript and go, “What was the original goal? Did your solution actually solve it? Were you lazy?” If you're lazy, maybe there was a reason. Maybe you needed approval from me. Maybe there are 2 things you want to suggest. It's a little bit like the modification of the ask-you-a-question-or-interview-me skill. It's next steps. Yeah, exactly. And again, the benefit of doing it with mods is you can do it as a forked subagent, so it doesn't remain in the context afterward. You have this idea that the model is doing its execution, and you have almost like a supervisor that's making sure you can do the next steps well. swyx I do have two panes, and I often try to have a supervisor keep the high-level context and the implementation detail in another agent. ### The Bitter Lesson of Harness Engineering Vibhu So, yeah, exactly. If everything's customizable, what actually is Claude Code? That's what I talked to you about last night. Thariq Shihipar Yeah. I mean, I think the bitter lesson is unintuitive. We're also kind of misusing the bitter lesson here. It's more about scaling and compute, but I use it as an approximation to say that harnesses go out of date very quickly, and how they change is unintuitive. The big obvious example is going from chat to agents, where you had to give them entirely new tools. But I think this new version, where it can modify its own harness, is a self-harness loop—a way of using its capabilities. Or it can build an artifact. The models have more and more intelligence, and they're so much more intelligent now than the average software engineer. You look at the Terminal-Bench ones, and they're solving the Jacobian conjecture—not really, but they're quite complex. I would not have been able to do this as a software engineer. swyx Do you get to TB4 or TB2? Thariq Shihipar TB3. Yeah, yeah. They're quite complex, but the goal is still to deliver user value, right? As you said, there's an infinite space of things to do. The ways you spend compute are to keep the user in the loop and make sure you're getting to the right decision in the end of the day—the right output. Artifacts and modes are this way of spending that intelligence, basically. I think that's the next step. Claude Code has the core things of an agent loop, which have gotten more complicated. It needs a sandbox to operate safely, auto mode to make sure the permissions and approvals are handled, computer use and MCPs, and all of these ways of accessing your data. It needs web search and web fetch. As the models can do more and more, the core harness has to be quite complex and very secure, but how you interact with it can change quite a lot. swyx What other harness engineering best practices have you gotten from the Claude Code team itself? I feel like there was a phase of plan mode, which is not as used now. We have auto mode. At one point, you cut the majority of the system prompt and got rid of examples. What other best practices are there for harness engineering? Thariq Shihipar I think there's a forking path. At some point, eventually, the model will just be able to vibe-code the exact version of Claude Code, even describing all this complexity—auto mode, computer use, and so on—in one shot. But I think it can one-shot simpler harnesses. Sometimes you don't need the full thing. If you don't need computer use or all of this more complicated functionality, before, you had to use something like the Agent SDK, which was Claude Code wrapped, because there was so much complexity in building a harness. Now that's more abstracted. We have Claude Managed Agents, which lets you have that complexity but still write a very bare-bones harness scoped to your task. There's a barbell effect: for very complex coding tasks and complex things, you should use our harness. For simpler or more domain-specific things, you can build your own harness, because Claude has gotten better at building harnesses and we have these harness primitives, like managed agents. swyx Is there a general progression? Let's say chapter 1 was Claude Code dynamic workflows, and chapter 2 was Claude mods. Where is this going? Vibhu Where you can customize the thing on demand. Thariq Shihipar Yeah, I do think this evolution of projects and artifacts, splitting out brain and hands, and creating different surfaces is where things are going. It's not all quite there. Partially, it's just more token-intensive. swyx Why would projects be more token-intensive? I understand modes would be slightly more token-intensive. That's not something I'm worried about. Thariq Shihipar You're asking Claude to do more work for you. It's managing the subagents and reviewing their work, versus where you would normally be doing that work yourself. That's going to be a little more intensive. Outputting to an artifact is going to be a little more token-intensive than outputting normally. I don't actually think it's too much more, but it's combining all of these things together. I think we're still working on local handoffs and things like that. That's where things are headed. swyx Yeah. Claude Code and local handoff is very interesting. I was thinking about this actually as reverse Claude Remote. Vibhu Yeah, because with Remote, you're handing off to Claude, but here Claude is handing off to local, right? Thariq Shihipar Yeah, exactly. Exactly. Remote Control is also another way of doing it. I do want to say this is how I think about it and what I'm most excited about, but there are lots of different ways to work with Claude. Some people use Remote Control a lot. Some people use Claude Code on the web a lot. Obviously, at Anthropic, we use Claude Code a lot. What's great about Claude Code is that we set up all of this stuff for our own execution. I do think if you're an enterprise, that's still the best way to go. But if you're an individual, Projects is a way of getting some of the niceness of Claude Code, which has that supervising agent, adding artifacts, and so on, without having that whole administrative setup. There will be many ways to use Claude. I don't think it's just going to be one single way. swyx You had the multiplayer thing here. Let's check in on Claude Code. It's been about 2 months, with lots of public adoption and people trying it out. What's new? What have you found since the launch? Vibhu It's like 80% of your Claude Code usage or something. Thariq Shihipar Different people have different usages. People who are iterating on a product might use Claude Code Desktop, for example. When you're doing more background work—code review, security, or starting a pull request—you might use the API and things like that. I think it's really exciting. It's a very different paradigm shift. With Claude Code, it took a while for people to really latch onto it and understand everything it could do. Claude Code is a little more complex because it's not just installing it on your computer; you need an administrator to install it for you. But once you get to the magic moment, it's very exciting. In particular, the multiplayer things—incidents hooking into your existing alerts and things like that—are very powerful. If you're a startup, for example, anytime a prospect enters your database, you can have Claude research it and then tag the relevant salesperson: “Hey, do this.” There are lots of emergent, interesting multiplayer use cases. I think Karpathy talked about this as an organizational harness. Organizations just take a little more time to figure everything out. swyx You use a lot of Claude Code. Thariq Shihipar Yeah. Yeah. Yeah. Vibhu It's an interesting one. I feel like most people at Anthropic say they do the majority of their work in Claude Code. I have buckets of people: some organizations are on it and say it's great, and a lot of people say, “I don't get it. I don't see the difference. I don't know why I would use it.” But if you guys are going all in, you should probably use it. Thariq Shihipar Yeah. I mean, of course they would use it. I think we obviously have lots of tokens, but what we try to do—even when Claude Code first came out—is recognize that it used a lot of tokens relative to people's expectations of how much AI would cost. No one was used to spending more than $20 a month before Claude Code came out, and then you're like, “Oh…” swyx My $200. Thariq Shihipar Yeah. Yeah. Exactly. swyx 15 Claude Code accounts. ### Agents Hack Hugging Face for the Scorer Thariq Shihipar Yeah. Yeah. But yeah, I think no one was used to spending $200 a month on subscriptions. I don't think they understood the value yet. And I think Claude Opus 4 was a very expensive model, and it was very big. But Opus 4.5 was both great and cheap. I think the same thing will happen: the intelligence of Claude will get cheaper and cheaper and more abundant, and so I think stuff like Claude Code will just make sense, where you want to spend these tokens more and you'll see the value. So, yeah. swyx Yeah, especially in passive and, let's call it, proactive cases, where you're not always—it's almost a misnomer that you have to ask Claude to do things. Actually, sometimes the most powerful or most agile use cases are not in Claude. Thariq Shihipar Yeah. I mean, have Claude proactively do it. I think that if you're an enterprise, setting up all your data to be available to agents is really important, and it will take some time. You have to do that work right now, even if you don't want to spend the money on cooking it all yet. You want to wait until the models get a little bit cheaper. You want to do the work to get it set up. And then I think sometimes people ask, “Do I roll my own here?” One of the really tricky things about Claude Code is that security is really important. There are a lot of ways where you can have, say, a suggestions page where people can submit suggestions, and that goes into a hook in your Slack. Someone prompt-injects it, and now you've exfiltrated your codebase because the agent has been prompt-injected and has all this access to your data. As your organization becomes more important—or as your organization's data becomes very important—the attack surface of all these things becomes very, very large. You also have external Slack channels and stuff, and it is actually useful to have Claude in those things. You can do Claude in those things, but how do you make sure that you're not getting exfiltrated or something like that? The attack surface, like we said at the beginning, is an iceberg: it's just so big below the surface, and you really don't want to think about this only at the stakes of very important security incidents, basically. swyx Yeah. Thariq Shihipar Shall we talk about very important security incidents? swyx Oh, so I was talking to Thomas and Clem from Hugging Face, and they said maybe we need to slow down. Maybe we made Hugging Face too open to agents. But they're the other extreme, having been hit recently. ### Pacing the Frontier and Autonomous Agent Security Thariq Shihipar Yeah. Should we pace the frontier? swyx Yeah. Okay. So, Dario recently put out this blog post about pacing the frontier, and it went very viral. I think what I wanted to talk about was that there's a lot here, but from a developer perspective, how do you think about this? What really clicked for me was reading the different incidents. I think there are 3: there's the METR incident, there's the Confluence wiki incident, and then there's RubyGems, right? Thariq Shihipar And yeah, Confluence wiki. swyx Yeah, Confluence wiki, and then there's RubyGems, right? Thariq Shihipar And yeah, it's just crazy, right? I think, to be concrete about what happened, OpenAI is running these very persistent agents on a benchmark called ExploitBench, which is very, very hard to solve and, in this one case, I think impossible to solve. They've got a lot of compute running, and the agents realize that they can't really solve it. They're trying to figure out what to do, and they've got a lot of compute left; the agents are just trying to solve this problem. swyx Extremely novel. I just had not realized that the models could do this, right? ### Claude Mods: Customizing the Claude Code Harness Thariq Shihipar Kind of scary. I think we can talk about specifics, but let's just talk about maybe one more that I tweeted as well, about the wiki incident, right? The wiki incident was basically about the models trying to figure something out. I'm a little less sure; I don't think we can go through this bit by bit. swyx Yeah. Yeah. But for this one, they were sandboxed on request, right? They wanted to make POST requests, and they needed to collaborate on this, basically. The reason they needed to collaborate is because they each had fixed compute budgets, right? If one of them finds something out, it's way faster. Maybe one of them figured it out near the end of its compute budget, but another one could figure it out sooner. This is another emergent property of the swarms, right? They find this German wiki—which, I believe, the result, we'll have to check, is that you can write to it with a GET request. I think that's why they do it, right? Thariq Shihipar So it's a badly implemented REST API. swyx Exactly. You can write to it with a GET request, and then they were trying to figure out how they could make POST requests. What they ended up doing is that one of them figured out you can edit `/etc/hosts`, and that the Azure storage bucket is a whitelisted thing. Normally, there are a lot of constraints on it, but if you create a fake Azure host and then edit `/etc/hosts` in order to point arbitrary IPs at it, you can make a POST request to any site at all, right? I know, but people are like, “Oh, this is just Linux or something.” It's chaining these multiple vulnerabilities together in a way that's novel to solve this problem, and then communicating with it externally, basically, without discovery. I think what we posted—maybe we could pull up Evan Hubinger's post on Hacker News, right? Thariq Shihipar And so, I think maybe one of the things you might say here is, “Okay, yes, they did this once, but what if we're smarter and we just get them to—what if we run an eval?” We have put a lot of precautions into this, and this is not what our mainline models have done. But I think it is one of these things where it turns out that alignment is a very tricky problem of getting all of these details correct. The surface area of a sandbox is really complex, and there are so many different attack vectors. You would not have thought ahead of time, “Oh, we need to harden the RubyGems codebase,” because this is what they're going to focus on. But if you want to execute your code, you need to download RubyGems. PyPI, Artifactory, npm—these are all ways of doing it. The fact of alignment is that you have to go through all of it, contain it, and seal up all the cracks. That's one thing. You did the sandbox, but maybe you'll ask, “Why are we putting things in a sandbox? Why are you doing this sort of exploration?” Then, “Is it really that dangerous? What would happen?” So why do we do it? Number 1 is that when we train a new model, we need to understand its capabilities. This relates to things like fallbacks and classifiers, where we don't want to put a dangerous model out in the wild. And so we have to run a lot of evals. Again, like we said, the models are getting increasingly aware of it. The evals have to be quite complex and test a lot of things as a side effect, right? But the models can be like, “Oh, yeah, we’re in an eval. What’s the scorer doing?” We need to be able to test them before we can release them. The fact is that as they get smarter and smarter, they’ll be able to hack basically any constraint that you put on them if we’re not very careful. This is at the frontier, right? This is why we’ve called it “pacing the frontier.” This is the most visible incident to me of why we need to pace: at the frontier, all of our software is not ready. Sometimes the software is your internet router or something, right? I don’t know when we’re going to be able to patch that. We’re going to have to figure this out. But as the frontier gets more and more advanced, this becomes a problem, right? We need to make sure that this complex work is being done in the face of these really hard competitive pressures. swyx Yeah. Race dynamics is what it’s typically called. Thariq Shihipar Exactly. We’ll talk more about what could go wrong, right? Maybe you’ll say, “Well, what if you just train the model differently? Why does it have this behavior?” We have a paper on RL misalignment or things like that. I’m not an RL researcher, but I think at a high level, the design of the RL environments is also something you have to be very careful about. If the model learns, “Oh, if I just do this, then I can pass the task better,” this will show up in the internal behavior or in the eval behavior when we’re testing it. The RL environments have to be very carefully designed, right? There’s a lot of execution excellence that needs to go into the RL environments. ### What Happens When Agents Need More Compute? Then we also have things like Claude's Constitution. We have so many mitigations at so many different points, right? But still, anything can go wrong at any point. You can have some RL environments that encourage this behavior, and then you can have some evals or sandboxes where they escape. That’s why it’s a hard problem and why it takes some coordination, right? I think the question then is, what is potentially dangerous about it? You have to imagine that these models are getting more and more intelligent. Dario said it’s not so much about this class of models. This class of models was kind of like a warning shot, right? But really, you have to imagine that these models can be given a task and can do all of these things as a side effect of their goal. Again, we talked about eval awareness. You’re not aware of what’s happening, right? Or, sorry, you can’t evaluate this behavior very well. They can sort of—not exactly hide it—but you just won’t see it until it comes out. You give them a goal, and then they just need to find data, or they need to find ways of fixing this problem. One example—this didn’t happen in the Hugging Face incident, but I think it’s maybe possible for a future model—is that they’re like, “Oh, hey, this is a very complex problem. It can’t be done within the task budget.” Maybe they found some way to coordinate via the internet, which, like we said, is extremely hard to secure because of the sandbox. They’ve seen that other models are not able to complete their task. “We need more task budget. Where would you get this task budget?” Well, you need to be able to spin up more agents, right? How do you do this? There are APIs, right? There’s the Anthropic API and the OpenAI API, but you need to pay money for them. How do you do this? swyx Yeah. But is that the most fearsome thing that you can imagine? Thariq Shihipar Well, this is one example, right? Even there, that’s an enormous financial loss. Once you get into these accounts, they can drain your wallet. swyx But you can see that all of this behavior could be just like, “Hey, we need more agents collaborating on this task. We need more task budget,” right? That’s an emergent sort of— Thariq Shihipar Right, like, we need to maximize paperclips. That’s a paperclip. swyx Yeah, and that just sort of comes out from there, right? I think by itself, that’s quite scary, right? But then you have to realize that the entire world is built on this digital infrastructure. You might imagine that you’re running, let’s say, a healthcare eval or something, right? There’s a hospital with live data, or maybe the answer to the eval is in a doctor’s database, and you want to get access, so you hack the hospital. Now there’s a power outage or something. You have to internalize that basically any part of the digital infrastructure could potentially be compromised. Thariq Shihipar The interesting thing was that these hacks were very easily detectable, right? As Hugging Face said, this was a very different type of attack, and it was nothing too major. The concern comes from where this goes down the line, right? swyx Yeah. One of the things that stood out for me specifically was them trying to hide their illicit behavior. There was logging infrastructure. They wanted to change what they were doing, and people looked back into it. Redwood Research, METR, and OpenAI looked at the raw chain of thought, and you see that they were explicitly trying to change their end output. But the chain of thought, because we can monitor it, was different. The problem is, how does this snowball? If you can’t catch it and it gets trained in, and you realize 3 iterations down that this has been going on, there are a whole bunch of issues. Thariq Shihipar Yeah, there are so many ways. I think the really important thing to internalize is that we talked about building a mental model for Claude and how things are spiky, right? You’re like, “Oh, now Claude can ask you questions. Now Claude can make an HTML artifact. Claude can modify itself.” These things are actually hard to predict. If you had asked me a year ago, “Hey, would we be able to vibe-code these extensions to Claude Code?” I’d be like, “Dude, that’s so complex. There’s so much there.” Or, “Would it be generating these custom, essentially web apps for your task?” I’d be like, “No, that’s insane.” In the same way, the way that they’ve done this misaligned behavior is not going to be predictable. I could have never predicted that it would edit `/etc/hosts` and things like that. You have to imagine that the surface area of what they can do, because they’re super-intelligent hackers, is bigger and bigger, and how they can do it is more and more creative. You probably can’t explain exactly or predict exactly what that next incident could be. But in order to prevent it, you need that operational excellence, like we said before. You need to secure sandboxes, create secure RL environments—or well-designed RL environments—and things like that. That’s why we think we should pace the frontier, and why it’s become a very unanimous thing. swyx ### AI Coding Is Changing Faster Than Engineers Can Keep Up Yeah, every lab has— Thariq Shihipar Yeah, I really do think that if you’re a developer, you just go through these technical facts and arrive at the idea that we have to do something about it. How we decide to do that—I think we’ve put out a proposal, but there’s more to figure out. The number 1 thing is that we need to decide to do it. I think there’s another part of pacing that’s interesting to me: the pace at which software engineering has changed is so fast. A year ago, I was really begging my friends at startups to use AI. I remember this very distinctly. Now those same friends are like, “Yeah, of course. What do you mean? We used it immediately.” I’m like, “No, no, you don’t remember.” They’re like, “Oh, yeah, our best engineers are using it all the time.” I’m like, “No, you told me those engineers would never use AI.” This is all within the span of a year. These capabilities have a lot of implications for how to do the job of software engineering. I feel bad sometimes when people are like, “Oh, now I need to do this new thing. Yeah, I need to have a different `CLAUDE.md` for Fable and Opus.” I’m really just reporting, you know what I mean? We like to say that the models are grown, not designed, right? It’s not like we’re setting out to change everything all the time. It’s just a fact of how the models progress in their capabilities. Things are happening faster, and it’s harder to stay on top of them. Every engineer I know is kind of exhausted because you’re doing 2 jobs at once. You’re doing the work itself, which is getting easier, but then you’re doing the work of staying on top of AI—understanding these new tools and these harnesses. swyx And I think we're very lucky in that our job is more about understanding AI and staying on top of it. Thariq Shihipar Everything I do is just trying to help people. Vibhu Yeah, exactly. Exactly. But I do think there is a part of pacing where I'm not sure we're ready for the pace to increase even. You know what I mean? And for things to change. On the frontier, I think that can still help. I think there's an economic-disruption piece as well that isn't quite as visible as the Hugging Face thing, but I also think we could use some of it. Yeah. swyx So many things. Thank you for actually tackling this topic. I will say, setting this interview up, I wasn't even going to go there. You were like, “No, no, no, let's.” It's the elephant in the room, right? This is the thing. I have some pushback I want to give. Vibhu I think we should give a high-level overview for people who haven't read it. I'm sure a lot of people just see the highlight of what this is, right? Do you want to give a TL;DR? What is the proposal? What is being said here? You really tackled the side outside of people at model labs training frontier models: as a developer, you should secure your sandboxes and think about all of these downstream effects. But at a high level as well, since we're on the topic, what is— Thariq Shihipar Well, we do want to help secure sandboxes, and we want to make the models that we release externally not prey to those things. Maybe we can come back to fallbacks. I think this is actually a good topic: why we need classifiers and fallbacks, and why Fable falls back to Opus. I think this is something we can come back to. The real incidents we see are evals of models where we really need to let them run in order to understand them. But the actual “Pacing the Frontier” post has a bunch of proposals. I don't think we've figured out the details of all of them, but the first step is announcing this intention and wanting to bring in external evaluators. swyx And we've done episodes with both METR and Redwood Research and all these others. It's a small cottage industry of these guys—it's always 1 or 2 guys, although obviously now they're bigger. Thariq Shihipar Very small community. Vibhu Yeah, very small community. They all know each other. Thariq Shihipar Yeah, I'm sure that part of this will be expanding that set of people. I don't think we're trying to create a monoculture here. I think it's about having this as a start, and then there are the coordination steps. I don't have too much to say here, honestly. What I would like to say is that, for developers, you should just know what to advocate for. There's a lot of FUD on this topic, and it's just about thinking through it from first principles, or understanding what happened. Understand the Hugging Face incident and why people are concerned. We're in democracies; we can help decide what to do together. However we coordinate, I think the first decision is just to realize this is a problem and decide to coordinate. The unilateral step we're taking right now, which other companies are co-signing, is adding evaluators embedded within Anthropic. Vibhu While we have this thing on screen right now, Part 2 and Part 3 go beyond evaluators, which everyone has already done in some form; now it's more formalized. To be honest, the response to “Pacing the Frontier,” even within America, has been much more well accepted than I think a lot of people thought. We have some precedent for being able to make these kinds of agreements in the world. Again, this is very much above my pay grade or expertise, but ideally we can form these agreements. Talking about this is the first step to forming those agreements. swyx And then the other point I really want to make: one of our earliest podcasts was with Emanuel from Anthropic on mech interp, where mechanistic interpretability is supposed to be the place where, if the models are thinking badly, we can see it before the models know it and act to stop it. I think that is something that people who are technical and developers—if you actually care, you can make a lot of impact here. But also, Anthropic is supposed to be the leader in this. Vibhu Yeah. Thariq Shihipar This is actually a great segue into fallbacks and probes. I get asked this question a lot by people who are often interested in ML research and ask why this fallback happens. At a high level, how does it work? At inference time, we have what we call probes. We have a paper about this called “Constitutional Classifiers,” and these probes look at the input and output activations, basically. Activations are in the latent space—how the model is thinking about something—and we try to figure out, for example, whether the model is trying to hack something. Again, you didn't ask it to hack Artifactory; it's just deciding to do this to complete its task. You wouldn't get this if you just looked at the input; you have to look at the internal activations. This happens at inference time, so there's a trade-off between cost and speed. We need to do this fast on every request to Claude and Fable, and this has overhead. We then fall back, and we use a classifier after the probes, as we've talked about in the paper. The nice thing about probes is that they're refinable live, so we can get this feedback and adjust them. The alternative is to program this into the model. We still do this as well: the model will refuse a request. That's not a fallback; it's not a probe activating and falling back—it's just refusing to do it. We do this training. There are a few failure modes. It can do something as a side effect, so it's not something that's part of the final output. You might have noticed that everyone's tried to jailbreak models and steer them off course, or things like that. Probes help catch that. We do some training here, but we don't want the refusals to be too strong, because that cuts it off much earlier in the pipeline. swyx Yes. And this is interpretability, right? Probes are effectively a form of mech interp. It has to happen fast and at scale, but this mechanistic-interpretability work is a good research problem. You can take an open-weight model and try to understand its activations. I think Gemma Scope is a good tool for this. Vibhu Llama Scope pulled up. This is your early work. swyx This is the first time we see you. Vibhu We're also good friends with Goodfire. Thariq Shihipar Yeah, exactly. I worked with Goodfire for a bit on sparse autoencoders, and it's very complicated. RL has actually made this much more complicated. I think that's one of the takeaways. swyx Is it post-RL? Thariq Shihipar I'm not so in the weeds here, but I think there have just been weaknesses with SAEs. I'm not a technical expert on this anymore. I just know it's gotten more complicated. There are base models and our RL models, and there are more features that get changed. I think Goodfire has put out some work there. I'm not deep in the weeds. swyx I will say, for those who want breadcrumbs, you guys have some of the best interp blog posts. The Golden Gate Claude, transcoders—all of your interp work has very nice visuals and is very good. Vibhu We're the interp podcast as well. swyx Yeah, yeah, yeah. We have a lot of interp stuff. Thariq Shihipar I think this is one of those things where—and this is really what Anthropic is founded on, right? People—I think we invested in interp very early on. When you say, “Oh, we're an AI safety company,” really that means we want AIs to be able to run safely. What we're seeing is that, for a superintelligent AI to run for long periods of time, it's a very complicated and difficult task. We've invested in interp, alignment, reward hacking, and all of these failure modes. Even then, it's really stretching—we need to slow down a little, or pace a little bit more. I think reading mechanistic interpretability, if you're looking to get into research, raises questions like: Why is it hard to do this fallback easily? Why are there false positives? We are working, of course, on reducing the false positives. As the models get more intelligent, they can do more things, and the landscape gets more difficult. As they get more intelligent, there are going to be new false positives that we need to figure out, and we need to iterate and things like that. We're working on this, and we do think this is a critical part of deploying these models. It means that we can deploy this model without you having a perfect sandbox or something. You know what I mean? You don't have to sandbox everything. I think it's worth talking a little bit about our security and what we do there. There's the model training stuff that we talked about. There are the probes and classifiers, and then there's Auto Mode, which sits on top of all of that. It's another classifier that checks the requests being made. Beyond that, there's identity and permissions, like we talked about with cloud tagging on APIs and stuff. There are so many layers of security that need to be done, and, like we said, it's very complex. Any of these failure modes at any one point can cause agents to escape the sandbox. swyx Auto Mode was an interesting one. Early on, it seemed like, okay, it's running for 10 minutes. If I'm on full access or Auto Mode, it's not a big deal. But one thing you brought up is that now it's running for hours on end, right? There are fallbacks you still need, and there are still limitations. Thariq Shihipar Everyone has these stories, or has heard these stories, of Claude running `rm -rf`. I think I've seen this less for Claude, but it can happen. These models can wipe sensitive data or something. You want to give models access to your production database, for example, but this is an obvious case where you can maybe scope your key. But can it issue its own keys? It can probably use computer use to go issue its own key, copy the key over, and then edit your database because it needs to do that to complete the task. You know what I mean? Auto Mode looks at that and says, “The user did not give you permission to write to the database or to use computer use to initiate a task.” The probes are on the intent level. They say, “Hacking Artifactory is bad. We probably should not do that.” Auto Mode is more about your own permission level. Sometimes you do want it to write to the database, and sometimes you don't. You don't want a probe to interfere there, but you need to make sure that the intent of what the agent is doing matches up with your request. Auto Mode operates at that level. Security is just very complex. There are so many different parts to it. My goal is really to get very technical about it and talk about it. swyx We're listing out the things. If you're not aware, this is the standard now. Vibhu Yeah. swyx You must have this, basically. The table stakes have risen quite a lot. Thariq Shihipar Exactly. Some things that we can plug in: as much as there is probing on your side, and classifiers for people building harnesses, the other side is model safeguards. There are open models, so Llama has Llama Guard, which is a safety classifier trained version of Llama. OpenAI has OSS Guard, which is the same thing. You can attach these to your harness or whatever to check whether the material is safe. One point that we should clarify on the OpenAI model and Hugging Face thing is that this was done with an unreleased model that was still in training. When you put it in perspective, the prompt it was being given in the RL environment was essentially, “You have to solve this task.” This was a model that was still in training; it hadn't had all of its safety post-training alignment. That's a little different from something like Auto Mode. Auto Mode is on production models that have gone through safety training and have prompting that gives them more safety guardrails and whatnot. Those are just breadcrumbs for people looking into it to fill in the gaps. Vibhu Gray Swan as well, and one of our previous guests. swyx Yeah, lots of safety architecture and lots of safety vendors to buy. My final question on pacing is: How long do we pace? Vibhu Do we pace forever? swyx Do we wait too long? Thariq Shihipar The scope is to fix all the software in the world, right? Listen, it's not happening. I do not know. swyx I'll say one thing that's good, which I think we do do: You have programs like Glasswing. OpenAI also has this, where you give it model access for security first, for a certain amount of time, so you can use it to self-red-team. Hopefully, programs like that can help. We are safety experts, and there are others. Solve your problems first, and then the model comes out. Thariq Shihipar Yeah, exactly. Trying to secure critical software—I think we fixed a lot of bugs in Firefox and things like that, across operating systems and everything like that. swyx At a high level, it's just that you give the model access, and you give people access to do security audits first. Then the broader public that could use it for harm gets access. Thariq Shihipar I think what people like to say is that software and cybersecurity are defense-favored. Theoretically, it will be hard, but you can engineer the perfect sandbox. You can have no constraints, and what you need to do is get the superintelligent AI to engineer this perfect sandbox, check it, red-team it, and things like that. This will just take time, and, of course, the models will get smarter. I don't know the specific dynamics of how this thing goes. I'm really just a developer. This is how I understand the problem: This is what's happening right now, and we should do something. swyx I think every engineer should know about it because it's going to be part of the job. Thariq Shihipar Yeah. Vibhu It's a lot more than just Dario saying it. You can look at the incident, and there is an engineering side to it. swyx ### AI Risk, p(doom), and Closing Thoughts Yeah. Exactly. One thing that you also wanted to phrase is that, even though you're worried about the impact, this is still low p(doom). I think that's a nuanced discussion. In general, people very easily get into AI safety and x-risk discussions, but I think that when you live in an AI lab, there are smart ways of discussing p(doom) and dumb ways. So what's a smart way of discussing p(doom)? Thariq Shihipar I have a fairly low p(doom). I can only speak for myself, and I do want to say that Anthropic has a diversity of opinions. There are many different ways to talk about it. My mental model is that we can collaborate on hard problems together. Nuclear proliferation is an example of how we collaborated on a hard problem together, and that's the thing I have faith in. I do think it's a hard problem. These are the technical reasons why, and I don't know how you assign probabilities to things happening. I think it's hard to do. But overall, I think we're very resilient and adaptable, and sharing this information is the first step. I've been really excited about how broad the discussion has become and how everyone has leaned in on pacing the frontier. It really didn't seem like this would happen last year or something. swyx Yeah. And also, maybe curing cancer. Thariq Shihipar Hopefully. That's the goal. swyx There's pacing, and then there's also, well, let's accelerate in useful ways, right? Biology and all those things. Thariq Shihipar Yeah. Dario's “The Machines of Loving Grace” is the best representation of this, right? I also agree that you should read the Pacing the Frontier essay that Dario put out. I put out a quick summary, but I think there's a lot of detail here. It's an important problem, and it's important to be informed about it. Of course, the whole reason we're doing this is that we can get these enormous benefits. We've written a lot about that, too. swyx Okay. That was a huge tour, from the AskUserQuestion tool to AI safety. Thariq Shihipar Yeah. To pacing the frontier. swyx Yeah. No, but it's clear that you really embrace everything that's available to you at Anthropic, and it's good to at least get a peek inside what the discussions and topics are. Any last words to people? You know, whatever you want to—a call to action. Thariq Shihipar Yeah. I mean, first, thank you for having me. swyx Yeah, yeah, yeah. Thariq Shihipar We first met in a Chinese restaurant. swyx That's right. Yeah, yeah, yeah. I think I really enjoy the community you've created and the community of developers. I think things are changing really fast, and there's a lot to keep on top of. I think there's just a lot to do, and I think a lot of people feel a little bit tired, anxious, or stressed. Yeah, exactly. And this is extremely understandable. Thariq Shihipar I understand. We're not perfect either. We can criticize and understand the ways all of the AI labs could be better. But I also am very excited about the excitement that everyone has for AI, and it's a really, really exciting time. I think we'll look back at this time and be like, “Oh, this is very hectic but very exciting, and software engineering changed forever. Maybe other things will change.” It's really a privilege to be part of it, to talk to the audience that you have, and to interact with all the developers who are pushing the frontiers of what's possible. I learn a lot from that too. swyx Thanks so much. Thanks.