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Posted by dhorthy 4 hours ago

Why Software Factories Fail (or: harness engineering is not enough)(github.com)
104 points | 80 comments
fishtoaster 1 hour ago|
There's some good ideas and points in here, but this bit threw me:

> # We tried this > In July 2025 we went full lights-off

Isn't it pretty well-accepted at this point that the models underwent a step-change in usefulness around fall 2025 / spring 2026? I know that I was able to start handing agents whole features after that, but not before.

I feel like any perspective/experience on "what agents can/can't do" from before that period is... maybe less than relevant to the modern era. TFA calls it out a few sections later with "But surely the models have gotten better since then", but then just writes off any improvement. That does not match my experience.

tcoff91 1 hour ago||
Opus 4.5 was a massive step change in capability for sure. The opinions of anyone who hasn't bothered experimenting with these things post-Opus-4.5 are not worth a damn.

They still are far from perfect but they're massively helpful.

json_hero 1 hour ago|||
read. https://github.com/humanlayer/advanced-context-engineering-f...
2001zhaozhao 1 hour ago|||
I had a bit of this impression when reading the post as well as the authors' product website. A lot of it does seem to be stuck in 2025.

For instance I think their post "long-context isn't the answer" on their website post straight-up isn't accurate, and gives me the impression they are just extrapolating previous performance to new models. In my experience, Opus 4.6 and newer have worked very reliably for long context to me (i don't perceive any intelligence drop at 700-900K tokens). Yeah it's extremely cost-inefficient, but it works.

dhorthy 1 hour ago|||
my perhaps controversial take is that opus 4.1 was smarter than 4.5 for complex engineering work, but 4.5 was faster and "squishier" - it responded better to simpler prompts, it read between the lines of user input better, and that this was really important to converting new users quickly
json_hero 1 hour ago||
Did you even read further on? The section right after that addresses the step changes in current frontier models https://github.com/humanlayer/advanced-context-engineering-f...
dhorthy 16 minutes ago||
it is absolutely wild to me that this keeps floating to top comment thread when the guy very clearly did not read even the first half
Altern4tiveAcc 3 minutes ago||
>It's easy to be a little bummed by the core thesis here: "for now we're stuck reading the code".

>I was pretty excited for a world where we could just ask for things and let the models cook and not read the code and get beautiful production software

I feel so disconnected reading those things. Reading and writing code is what brings me joy. I'd never feel "bummed" or "stuck" with it.

rglynn 2 hours ago||
To me, the thing that stands out about the whole state we're in here is PR review.

Yes, in an ideal world, PRs read well, are a joy to review, reflect what you discussed etc etc. We have to be real; there is only so much we can do to that end.

I'm not sure how the best teams do PR review, from my perspective it sucks. I'm talking specifically about the UX. I've always hated Github's PR page, so I typically reviewed by pulling down the branch and opening the diff with $EDITOR.

These days I think there's really no excuse for the awful UX. Linear (a company that isn't even in the domain of code review) put out a basic PR review feature[0] that is already better than what GH offers. It's simple: point a small model at the PR, group file changes together based on theme, add some commentary and sort by importance (schema changes > openapi spec).

Immediately, so much mental load has been reduced without the reviewer or the requester doing anything. This feature is pretty damn basic, and I think there are obvious next steps like generating visualisations which a dedicated product could find the time to implement.

Keen to hear others thoughts on why this is the wrong approach, or if there are tools in wide use that solve for this, or why this isnt the right problem to focus on.

0 - https://linear.app/docs/diffs#guides

tcoff91 1 hour ago||
PRs sucked to review long before Agents were a thing, but now it really sucks because there are more to review.
xorcist 1 hour ago|||
> group file changes together based on theme, add some commentary

Isn't that what commits are? Or ... should be?

4lx87 1 hour ago|||
Gating integration behind code review is futile. I (and many other engineers) already automated it. My agent responds to review requests and reviews as me. Company policies enforcing human code review are futile.

I think all these platforms chasing code review are doomed. My LLM doesn't need any of this tooling.

We should be reviewing the actual working software. Systems that make it easy and instant to demo any proposed change are what is needed. Code (and specs) are going to fade into obscurity. PR review has already shifted towards validating the product (working software) over the process (code).

The future of software production is more like Replit – not GitHub.

tripleee 1 hour ago|||
What's your job as an "engineer" in this post-automated world?

QA?

roncesvalles 21 minutes ago|||
The role of a software engineer is foremost about the ownership of software systems, and secondarily about modifying them or developing new ones.

Software systems are like gardens (or owning a pet) - they need to be tended to, and somebody needs to know how they work. Software is not an artifact that you "make" and don't come back to until years later when it needs replacing, like a paved street.

Software development is not a "task" like designing a logo, it's a continuous operational undertaking.

4lx87 1 hour ago|||
Producing features and fixing bugs, same as it was before. The organizational process of software development has not changed much with AI: execs decide direction and initiatives, PMs decide what to build, which is broken down into features and bug fixes that SWEs produce. In my experience organizations don't actually care how SWEs produce features, except insofar as it relates to how many and how fast the features can be pumped out. Organizations see code review as a process to prevent bugs. Humans are not as good as LLMs at reviewing code for bugs. Abstract notions of code style and quality that programmers care about is not why organizations enforce code review.
20k 1 hour ago||||
>I (and many other engineers) already automated it. My agent responds to review requests and reviews as me. Company policies enforcing human code review are futile.

This is also known as being a terrible engineer. If a company enforces human review and someone deliberately tries to circumvent this with an LLM, I'd fire that person in an instant

The reason for human code review is:

1. So *you* understand what's going on, not the LLM, and people can ask you questions about it

2. Because LLMs are not that good at code review

It seems weird to brag about literally not doing your job. It sounds like you could be replaced with a python script, what value do you bring?

dhorthy 1 hour ago|||
blake smith has a really good post on this - that mental alignment among the team is the primary purpose of code review - https://blakesmith.me/2015/02/09/code-review-essentials-for-...
4lx87 57 minutes ago||
That is a good post. Thank you for sharing.

I can't help but notice that this person is speaking as a programmer, not the person in charge of employing programmers. Is that what the business values code review for? In my experience, managers enforce code review as a quality control mechanism: the "Find Bugs" step in the article's pyramid. And LLMs are already better than human reviewers at the "Find Bugs" part. Design and alignment with PMs and sales can happen before and after software delivery. At least that's how my employer sees it (and I suspect most other businesses).

It's a rough time to be a programmer who cares about the code, who understands software is a creative process, who understands that designing the software is intertwined with the code, who cares about systems. The hyper-focus on delivery was already a lot to deal with before LLMs.

amannm 1 hour ago||||
It seems weird to get angry about a change that is happening and will continue to happen due to what the market demands from software, which I believe will be the speed/ability to solve problems, rather than its own stewardship
computably 8 minutes ago||
Sure, if you're shipping a 500MB mobile/web app with a 5s start-up, it probably won't make a difference today, or tomorrow, or 3 months later. The problem is when your codebase is a dumping ground for AI slop and a year from now nobody can make any changes.

Also, it's not just some subjective value put in human review. If a change causes a major outage and it turns out it's because 5 reviewers were all shirking the company-mandated responsibility of review, and it could trivially have been caught, I would 100% expect those people to get fired. It's not a process issue if people are intentionally circumventing the process.

0xblacklight 44 minutes ago|||
this is exactly right
jfkfisksnsb 1 hour ago|||
[dead]
boron1006 1 hour ago|||
I just dont think LLMs are very good at judging importance or summarizing code.

I tried experimenting with what is ultimately a treesitter based approach - https://github.com/0x007BA7/codebook

And really liked it. Definitely nowhere near production ready but I think theres room for a player to come in and do something similar.

dhorthy 1 hour ago||
yeah that was another thing i hoped would pour through here - that deterministic systems are much better for evaluating quality (test, linters, cyclomatic complexity, etc) - but that we don't have such a system for code maintainability, at least not one that's widely accepted or adopted
claytonjy 43 minutes ago|||
thanks for pointing out the linear PR stuff, hadn’t seen that. Interesting that while a dozen other companies are trying to muscle in on the hosting/versioning side of github, rather fewer are working on the PR side.
2001zhaozhao 1 hour ago|||
I think the right shape is to review and merge directly from the agent window.
0xblacklight 43 minutes ago||
reviewing code as it's being written & re-steering it > reviewing it once 20k lines have been written
WorldMaker 1 hour ago||
> I'm not sure how the best teams do PR review, from my perspective it sucks. I'm talking specifically about the UX. I've always hated Github's PR page, so I typically reviewed by pulling down the branch and opening the diff with $EDITOR.

When $EDITOR = VSCode there's a shortcut on the GitHub PR page: if you type a . it opens in github.dev in a VSCode instance.

maerF0x0 10 minutes ago||
I'm currently learning about Cost functions and Regression in the Machine learning course on coursera[1], and I cannot help but be struck by the similarities of how gradient descent seeks to minimize the error between the model and the training data, how agents do the same (far less mathematically) to seek an acceptable solution to software problems, and how light evolutionary pressures seem to guide species towards a better fit solution to the problem of existence and reproduction. (I'm no expert on the evolutionary example so go easy on me!)

[1] - this course: https://www.coursera.org/learn/machine-learning/home/welcome

firasd 1 hour ago||
I think there is a fundamental issue here of what building software even means

If you think you can just assign Github tickets to AI agents and go drink daiquiris on the beach I think you'll find that you end up with more and more towers of abstraction and indirection. There are 'points of view' that emerge during coding I think. And at some point you as a human have to be like "wait... what if we use Redis here". "Wait.. the API is already returning the data we need". "Wait... let's not add customers to the report who have not been active in the past year". Stuff like that

claytonjy 36 minutes ago||
> There are 'points of view' that emerge during coding

I know it’s a bit cliche at this point, but this harkens to “programming as theory building”[0] which I agree is easy to lose out on when embracing agentic coding today.

[0]: https://gwern.net/doc/cs/algorithm/1985-naur.pdf

dhorthy 31 minutes ago||
I have had the phrase "programming is building a theory" spinning in my head for days, especially since watching this pragmatic engineer pod with Kent Beck https://www.youtube.com/watch?v=ddHQQtjIOpw
dhorthy 1 hour ago|||
yeah I 100% agree - and I think the most popular coding agent workflows / skill kits are designed to pull those insights and intuition out of humans in a way that optimizes for the developer's experience building the plans or building the code, e.g.

- claude code plan mode - mattpocock/skills - obra/superpowers - research/plan/implement

etc etc

piker 1 hour ago||
Hard to see them though if you’re not in the weeds and your agents are stacking abstraction on abstraction to pass tests.
dhorthy 1 hour ago||
yes exactly
AmericanOP 39 minutes ago||
The machine gives you what you ask for even when that thing doesn’t exist yet.

Rather than “lights off,” utilizing information theory, decision-making theory and creativity theory makes me better at asking for the right things.

Memory is not transcribed to weights like when humans sleep. Memory is notes handed to someone on groundhog’s day who can’t remember yesterday. We hope they believe us. Don’t be too surprised when a highly entropic system introduces entropy to a project over time.

zingar 26 minutes ago||
Enjoyed most of this but unconvinced by the program design part. If I see an agent writing function signatures or listing which functions to edit in a plan that tells me that I’ve given it too big a vertical slice. I always delete the code guesses. The thing that writes the code must always spend some time discovering where/what to write or it won’t have the right context. Or put another way: “decide first, act later” always feels worse than act-learn-act.
dhorthy 21 minutes ago|
one thing I probably didn't mention is we do the program design having already done an in-depth codebase research, with current patterns and architecture surfaced - that actually seeds every step of the flow including even the product part -

but yes if you're working in very small slices then I think it's very feasible to skip program design and just review the code as you go, and resteer live. I do this all the time for tasks that are too big for a oneshot but on the smaller side overall.

jadar 1 hour ago||
> So, why can't models do software maintainability?

I feel like the explanation does nothing to actually elucidate why models can't do it. Is it an inherent weakness of LLMs? Training processes? The typical "this is crap" that we constantly hear? It goes on to write about RL and how there's no penalty for bad design. But that sort of side-steps the question and makes you ask: "why not do RL and make a penalty for bad design?" Of course the models aren't good at it ... they're not good at anything until you've tuned them and put them in a harness that rewards good edits and throws away (improves) bad edits. That doesn't explain why "models can't do software maintainability." The real question is why harnesses can't do software maintainability, and how to build a system that can do it. (I suppose that's the purpose of the ad at the bottom of the page.)

jdlshore 15 minutes ago||
I think it’s because maintainability is a factor of software design, and good design is squishy and hard to articulate. There’s no good metrics for design. All the tools that purport to measure it are doing trivial things like cyclomatic complexity, and can only tell you when things have gotten really really bad, but not distinguish between “good” and “pretty bad.”

Design skills take about 10 years to develop, in my experience, and a lot of smart engineers go through a phase where they make gawdawful messes in the name of “magically easy” designs around the 5 year mark.

Design requires wisdom born of experience, isn’t measurable, and requires forming a mental model of how the system hangs together as a whole. It’s just not stuff LLMs are good at.

Fordec 1 hour ago|||
I have a hunch it comes down to the training data. We have spent decades as an industry talking up the new shiny thing, deliverables, frameworks, features, performance improvements, the one thing you don't read copious amounts of prose about is "how I maintained our system so that nobody noticed".
dhorthy 1 hour ago||
fair point, this is the thing I struggled most to extract out while writing it - if you can propose an RL environment that penalizes a model for bad design, then I'm all ears - right now there's no fast oracle/verifier for this (as stated in the post)

My current evolving take on "how would you build such a thing" is you need to tee up a roadmap of 20 features and feed them to a model one at a time, so it can't design up front for what's coming.

That way if it builds the first 10 features and the codebase goes to slop, it get's penalized when it can't build features 11-20, or when those features take wayyy more tokens/time/cycles than a model that maintains a clean codebase can do.

This is how most real software is built by most teams - incrementally, getting feedback from users along the way, and steering goals in response.

jadar 15 minutes ago||
Isn't that how AI written software gets better too? By steering the model towards the goals of the user?

I don't know if it's a question of how many features to feed to the model, either. Of course, overwhelm the context with too many features and it will get confused. But that's where the memory management idea that G. Huntley talks about is helpful. You're trying to steer the model within its memory limits towards a certain goal.

The problem is getting it to produce "good" code. Formalizing what that means is the task of the programmer. How do you steer a model towards always, or more often, producing good code so that you don't have to do rework? That's the same problem as with a junior engineer, but the way you do it is different. Right now we're trying to do it with mountains of prompts — which sort of works but has diminishing returns — and with onerous code reviews. We've seen this get better over time, but I think some more mechanical methods will help as we figure out how best to steer the models.

vanuatu 2 hours ago||
This is one of the best writeups I've seen of this

a lot of the model's constraints come down to how they are RLed. Discussions online would be a lot better if everyone understood how the labs train the models in a high level (or did a lil data labeling)

dhorthy 1 hour ago|
yeah i like this and others in the thread mentioned that understanding RL and RLHF and the shape of the data is really important (at least the fundamentals, I'm sure there's quite complex industrialization of RL inside labs as Nathan Lambert says)
mrbnprck 1 hour ago||
I've recently started experimenting with grounding LLM driven implementation/verification on RFC based normative specifications, to avoid having to manually steer the LLM during implementation and dealing with reviewing sloppy pull requests.

It works quite well, as it puts your entire focus on writing (hopefully) unambiguous specifications vs. having to discuss unwanted changes with an LLM during code-review. One flaw is that this only works great if you know exactly what you want, which is not always the case.

Lindby 1 hour ago||
But do you actually gain anything if you need to write detailed specifications? That seems just as time consuming as writing code, but less gratifying.

Code is just detailed specifications on how things should operate.

mrbnprck 1 hour ago||
Yes, actually that's what I'd had argued a few years ago as well.

It turns out that there are now a few more people that want to get their hands on building software, that don't necessarily understand code, but do have a fundamental idea of system design / requirements.

As you said code has always been a much more explicit representation of those specs, yet arguably introduces lots of noise, necessary to make the program compilable.

Us devs already had the obligation of writing technical documentation for non-technical people, just not at an explicit depth. From an efficiency PoV making that documentation more explicit is much cheaper than manually writing the compilable code. Hurts to say but AI got pretty good with the latter.

dhorthy 1 hour ago||
normative specifications can help, but the thesis here is that specs that define behavior of the product or even architecture are helpful but there's MORE that can be done and even though "program design" feels too in the weeds it's still essential if you care about maintainability
mrbnprck 45 minutes ago||
Isn't maintainability mostly about applying basic engineering principles e.g. separation of concerns, single responsibility, dependency inversion, open-closed etc..? If these topics are addressed in the normative representation, and correctly translated by an LLM into code (especially by slicing up the specifications into measurable outcomes to set the intended foundation), then future change e.g. maintainability becomes essentially easy as well, no?

Historically I know that the majority maintenance problems occur from slow continuous evolution of a system that it initially was never designed for. And the only way to address this was continuous system design.

dhorthy 40 minutes ago||
> Historically I know that the majority maintenance problems occur from slow continuous evolution of a system that it initially was never designed for. And the only way to address this was continuous system design.

yes exactly - this is what I'm advocating for - that you can't skip the system design, and that actually good system design goes down to the typedefs and object graph at the code level, not just mermaid charts and db schemas and service contracts.

I will highlight what a few others have said along the lines of "a sufficiently detailed spec IS code" - that is, to make the spec guaranteed to produce the code you want, the spec will look a lot like code (and will be roughly the same effort to review as the code itself anyway, saving you no time)

what I'm proposing is "how can you maximized the odds that the code WILL be good or close enough to good that its easy to get there, with the LEAST amount of human effort/attention" - how can you move fast without skipping what matters

https://haskellforall.com/2026/03/a-sufficiently-detailed-sp...

2001zhaozhao 1 hour ago|
> When I say maintainability, I mean the specific thing where it becomes really, really hard to change one part of the codebase without breaking another part.

The corollary of agents being bad at maintainability but good at coding is that you can vibecode all the parts where maintainability doesn't matter.

So if you build a (domain-specific) modular architecture for your software first you can then just let your software factories loose on building the modules.

throwatdem12311 1 hour ago||
Until you inevitably need a cross cutting concern.

“Oh just this one time”

Then an agent sees the pattern and assumes it’s a best practice. Then your beautiful architecture is ruined.

“Just this once” indeed.

dhorthy 52 minutes ago||
this is 100% right. you have to guard the codebase patterns with your life. because the codebase is part of the prompt.
dhorthy 1 hour ago||
yeah this is along the lines of what some friends of mine call "core vs. pragmatic modules" or even s/modules/codebase zones/

the idea that if you have a solid core and decoupled modules, you can have "zones" in your codebase where you allow the model to run wild and do a little slop, because you know the blast radius is contained

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