Dexter Horthy: Why We Stopped Trusting AI to Write the Plan

Dexter Horthy (0:00)

We wanted to be living in the future, and so we said, cool, let's try this. We'll set pull requests, but we'll just say, cool, if you read the plan, the code's not as important. Yeah, we did this experiment, we ran this for four or five months before we realized, oh, this code base is actually unusable now. It became slower and slower. Change over here, cause of regression over here. And then we decided, no, this is bad. And then we literally rebuilt the whole product from scratch. And the first two weeks of that, my co-founder, Kyle, was literally in VS code, not even cursor, typing every character by hand to plumb out the data architecture for the new version.

SPEAKER_2 (0:32)

The AI Native Dev is a podcast for developers and engineering leads at the cutting edge of AI and agentic coding. Join your hosts, Guy Podjarny and me, Simon Maple, every week as we chat with the most exciting voices in AI and tackle the biggest questions facing developers today. This is the AI Native Dev.

Yesterday, you were writing code. Today, you're prompting agents. Tomorrow, you'll be running a software factory. Agentic coding is moving fast enough to give anyone whiplash. This June, AI DevCon London sold out. Hundreds of developers, engineering leads and VPs packed in to hear speakers from Anthropic, OpenAI, Netlify, and GitHub cut through the hype and get to what actually works. This November, we're bringing it back to New York, bigger, bolder, and full of people actually building the agentic future. Three days of real talks, real tools, real answers, whether you're directing the agents, building the loops themselves, leading the teams, or setting the strategy. Our early bird pricing ends on September 30th, so make sure you lock in your place before prices increase. As a podcast listener, you can get 15% off your ticket using promo code POD15.

We have so much planned, and we can't wait to have you join us in New York.

Simon Maple (1:59)

Hello everyone, welcome back to The AI Native Dev. Thanks for tuning in. Today, we have a really fun conversation about software factories and how to do them or not do them, and how did we think and we didn't think and all that, and to dig into the timeline and really informed opinions about this. We have Dex Horthy, who is the CEO and co-founder of HumanLayer. Hi Dex. Thanks for tuning in here.

Dexter Horthy (2:22)

Stoked to be here.

Simon Maple (2:23)

Dex, you've done a lot of super interesting things beyond HumanLayer on it, but I think there were these sort of 12-factor agents that you wrote before, trying to kind of codify and explain how do we actually build agents on it. Today, I think you're starting to refer to like 12-factor factories on it.

Dexter Horthy (2:40)

Oh, you got that already?

Simon Maple (2:41)

Well, we just sort of know that you've done it. I actually don't know. Maybe we'll dig into that a little bit on it. And I think also what's sort of super interesting is that you've been sharing kind of strong opinions loosely held a little bit or maybe like changing over time. Maybe they were strongly held but pried out of your hands over time on it, which I think makes for sort of good insights and conversations to have. So thanks for tuning in. And maybe I'll kind of dig into it straight away, which is you've sort of changed your mind substantially and declaratively around kind of the way to do agentic development of it.

You know, really around specifically kind of lights off development, right, versus not. So what happened there? Like what did you believe before and what's the turnabout?

Dexter Horthy (3:33)

Yeah, I mean, the journey kind of starts around, you know, around when Opus 4 came out. And when they launched Opus 4, they also launched the Claude Agent SDK, which means you could use, it had a very small interface at that point. Right now the Claude CLI is basically like the JVM of agentic coding. It's got like 200 flags on it or, yeah, it's a fricking battleship.

But it was the first time you could use Claude, like small agentic loops as part of a broader, more deterministic piece of software. So we were building like terminal multiplexers for Claude code of like, hey, what would it look like to build a TUI where you can manage a bunch of sessions in parallel or like manage, get an inbox of like, what are all the approvals waiting on you and things like that. And we spent a lot of time trying to get, how do we get these agents to work for longer? It's very interesting. The biggest change between summer of 2025 and now is actually like the planning metagame. I don't think a lot of people realize this. A lot of people just write plans because they put plan mode in the thing or they read something online and they found some skills. They were going to make a plan. And I think depending on where you are in your journey and how the models have changed, in retrospect, I realized that writing a plan file in the summer, in July of 2025, the number one most high leverage thing that that got you was it was a really reliable way to get a model to work for longer.