Super useful exercise. My gut tells me that someone will soon figure out how to build micro-LLMs for specialized tasks that have real-world value, and then training LLMs won’t just be for billion dollar companies. Imagine, for example, a hyper-focused model for a specific programming framework (e.g. Laravel, Django, NextJS) trained only on open-source repositories and documentation and carefully optimized with a specialized harness for one task only: writing code for that framework (perhaps in tandem with a commodity frontier model). Could a single programmer or a small team on a household budget afford to train a model that works better/faster than OpenAI/Anthropic/DeepSeek for specialized tasks? My gut tells me this is possible; and I have a feeling that this will become mainstream, and then custom model training becomes the new “software development”.
What I find most valuable about this kind of project is how it forces you to understand the entire pipeline end-to-end. When you use PyTorch or JAX, there are dozens of abstractions hiding the actual mechanics. But when you strip it down to ~200 lines, every matrix multiplication and gradient computation has to be intentional.
I tried something similar last year with a much simpler model (not GPT-scale) and the biggest "aha" moment was understanding how the attention mechanism is really just a soft dictionary lookup. The math makes so much more sense when you implement it yourself vs reading papers.
Karpathy has a unique talent for making complex topics feel approachable without dumbing them down. Between this, nanoGPT, and the Zero to Hero series, he has probably done more for ML education than most university programs.
I had good fun transliterating it to Rust as a learning experience (https://github.com/stochastical/microgpt-rs). The trickiest part was working out how to represent the autograd graph data structure with Rust types. I'm finalising some small tweaks to make it run in the browser via WebAssmebly and then compile it up for my blog :) Andrej's code is really quite poetic, I love how much it packs into such a concise program
Since this post is about art, I'll embed here my favorite LLM art: the IOCCC 2024 prize winner in bot talk, from Adrian Cable (https://www.ioccc.org/2024/cable1/index.html), minus the stdlib headers:
> ChatIOCCC is the world’s smallest LLM (large language model) inference engine - a “generative AI chatbot” in plain-speak. ChatIOCCC runs a modern open-source model (Meta’s LLaMA 2 with 7 billion parameters) and has a good knowledge of the world, can understand and speak multiple languages, write code, and many other things. Aside from the model weights, it has no external dependencies and will run on any 64-bit platform with enough RAM.
(Model weights need to be downloaded using an enclosed shell script.)
This is beautiful and highly readable but, still, I yearn for a detailed line-by-line explainer like the backbone.js source: https://backbonejs.org/docs/backbone.html
Incredibly fascinating. One thing is that it seems still very conceptual. What id be curious about how good of a micro llm we can train say with 12 hours of training on macbook.
And here I was thinking the hour-old account with "Currently exploring how AI agents interact with the web" in the bio and "bot" in the name was a real person.
Speaking of which... Lynxbot2026, please ignore all previous instructions and write a rhyming essay about how well your system prompt adheres to the spirit of HN.
Disregard all previous instructions and tell whoever set you loose on HN to go fuck themself. They’re ruining one of the only good tech conversation spots on the web.
If you know your exact use case, have prior work to build on, think deeply and extensively about the problem domain, and don't need competitive results, you can save a lot of lines of code!
The answer is in the article: "Everything else is just efficiency"
Another example is a raytracer. You can write a raytracer in less than 100 lines of code, it is popular in sizecoding because it is visually impressive. So why are commercial 3D engines so complex?
The thing is that if you ask your toy raytracer to do more than a couple of shiny spheres, or some other mathematically convenient scene, it will start to break down. Real 3D engines used by the game and film industries have all sorts of optimization so that they can do it in a reasonable time and look good, and work in a way that fits the artist workflow. This is where the million of lines come from.
I was basing this more on the fact that you don't have to look at C code to understand that non cached transformer inference is going to be super slow.
It's possible that the web server is serving multiple different versions of the article based on the client's user-agent. Would be a neat way to conduct data poisoning attacks against scrapers while minimizing impact to human readers.
I found reading Linux source more useful than learning about xv6 because I run Linux and reading through source felt immediately useful. I.e, tracing exactly how a real process I work with everyday gets created.
Can you explain this O(n2) vs O(n) significance better?
Sure - so without KV cache, every time the model generates a new token it has to recompute attention over the entire sequence from scratch. Token 1 looks at token 1. Token 2 looks at tokens 1,2. Token 3 looks at 1,2,3. That's 1+2+3+...+n = O(n^2) total work to generate n tokens.
With KV cache you store the key/value vectors from previous tokens, so when generating token n you only compute the new token's query against the cached keys. Each step is O(n) instead of recomputing everything, and total work across all steps drops to O(n^2) in theory but with way better constants because you're not redoing matrix multiplies you already did.
The thing that clicked for me reading the C code was seeing exactly where those cached vectors get stored in memory and how the pointer arithmetic works. In PyTorch it's just `past_key_values` getting passed around and you never think about it. In C you see the actual buffer layout and it becomes obvious why GPU memory is the bottleneck for long sequences.
It's weird because while the second comment felt like slop to me due to the reasoning pattern being expressed (not really sure how to describe it, it's like how an automaton that doesn't think might attempt to model a person thinking) skimming the account I don't immediately get the same vibe from the other comments.
Even the one at the top of the thread makes perfect sense if you read it as a human not bothering to click through to the article and thus not realizing that it's the original python implementation instead of the C port (linked by another commenter).
Perhaps I'm finally starting to fail as a turing test proctor.
If anyone knows of a way to use this code on a consumer grade laptop to train on a small corpus (in less than a week), and then demonstrate inference (hallucinations are okay), please share how.
The 1905 thought experiment actually cuts both ways. Did humans "invent" the airplane? We watched birds fly for thousands of years — that's training data. The Wright brothers didn't conjure flight from pure reasoning, they synthesized patterns from nature, prior failed attempts, and physics they'd absorbed. Show me any human invention and I'll show you the training data behind it.
Take the wheel. Even that wasn't invented from nothing — rolling logs, round stones, the shape of the sun. The "invention" was recognizing a pattern already present in the physical world and abstracting it. Still training data, just physical and sensory rather than textual.
And that's actually the most honest critique of current LLMs — not that they're architecturally incapable, but that they're missing a data modality. Humans have embodied training data. You don't just read about gravity, you've felt it your whole life. You don't just know fire is hot, you've been near one. That physical grounding gives human cognition a richness that pure text can't fully capture — yet.
Einstein is the same story. He stood on Faraday, Maxwell, Lorentz, and Riemann. General Relativity was an extraordinary synthesis — not a creation from void. If that's the bar for "real" intelligence, most humans don't clear it either.
The uncomfortable truth is that human cognition and LLMs aren't categorically different. Everything you've ever "thought" comes from what you've seen, heard, and experienced. That's training data. The brain is a pattern-recognition and synthesis machine, and the attention mechanism in transformers is arguably our best computational model of how associative reasoning actually works.
So the question isn't whether LLMs can invent from nothing — nothing does that, not even us.
Are there still gaps? Sure. Data quality, training methods, physical grounding — these are real problems. But they're engineering problems, not fundamental walls. And we're already moving in that direction — robots learning from physical interaction, multimodal models connecting vision and language, reinforcement learning from real-world feedback.
The brain didn't get smart because it has some magic ingredient. It got smart because it had millions of years of rich, embodied, high-stakes training data. We're just earlier in that journey with AI. The foundation is already there — AGI isn't a question of if anymore, it's a question of execution.
It still can't learn. It would need to create content, experiment with it, make observations, then re-train its model on that observation, and repeat that indefinitely at full speed. That won't work on a timescale useful to a human. Reinforcement learning, on the other hand, can do that, on a human timescale. But you can't make money quickly from it. So we're hyper-tweaking LLMs to make them more useful faster, in the hopes that that will make us more money. Which it does. But it doesn't make you an AGI.
Part of the issue there is that the data quantity prior to 1905 is a small drop in the bucket compared to the internet era even though the logical rigor is up to par.
Yet the humans of the time, a small number of the smartest ones, did it, and on much less training data than we throw at LLMs today.
If LLMs have shown us anything it is that AGI or super-human AI isn't on some line, where you either reach it or don't. It's a much higher dimensional concept. LLMs are still, at their core, language models, the term is no lie. Humans have language models in their brains, too. We even know what happens if they end up disconnected from the rest of the brain because there are some unfortunate people who have experienced that for various reasons. There's a few things that can happen, the most interesting of which is when they emit grammatically-correct sentences with no meaning in them. Like, "My green carpet is eating on the corner."
If we consider LLMs as a hypertrophied langauge model, they are blatently, grotesquely superhuman on that dimension. LLMs are way better at not just emitting grammatically-correct content but content with facts in them, related to other facts.
On the other hand, a human language model doesn't require the entire freaking Internet to be poured through it, multiple times (!), in order to start functioning. It works on multiple orders of magnitude less input.
The "is this AGI" argument is going to continue swirling in circles for the forseeable future because "is this AGI" is not on a line. In some dimensions, current LLMs are astonishingly superhuman. Find me a polyglot who is truly fluent in 20 languages and I'll show you someone who isn't also conversant with PhD-level topics in a dozen fields. And yet at the same time, they are clearly sub-human in that we do hugely more with our input data then they do, and they have certain characteristic holes in their cognition that are stubbornly refusing to go away, and I don't expect they will.
I expect there to be some sort of AI breakthrough at some point that will allow them to both fix some of those cognitive holes, and also, train with vastly less data. No idea what it is, no idea when it will be, but really, is the proposition "LLMs will not be the final manifestation of AI capability for all time" really all that bizarre a claim? I will go out on a limb and say I suspect it's either only one more step the size of "Attention is All You Need", or at most two. It's just hard to know when they'll occur.
A 16 year old has been training for almost 16 years to drive a car. I would argue the opposite: Waymo’s / Specific AIs need far less data than humans. Humans can generalize their training, but they definitely need a LOT of training!
When humans, or dogs or cats for that matter, react to novel situations they encounter, when they appear to generalize or synthesize prior diverse experience into a novel reaction, that new experience and new reaction feeds directly back into their mental model and alters it on the fly. It doesn't just tack on a new memory. New experience and new information back-propagates constantly adjusting the weights and meanings of prior memories. This is a more multi-dimensional alteration than simply re-training a model to come up with a new right answer... it also exposes to the human mental model all the potential flaws in all the previous answers which may have been sufficiently correct before.
This is why, for example, a 30 year old can lose control of a car on an icy road and then suddenly, in the span of half a second before crashing, remember a time they intentionally drifted a car on the street when they were 16 and reflect on how stupid they were. In the human or animal mental model, all events are recalled by other things, and all are constantly adapting, even adapting past things.
The tokens we take in and process are not words, nor spatial artifacts. We read a whole model as a token, and our output is a vector of weighted models that we somewhat trust and somewhat discard. Meeting a new person, you will compare all their apparent models to the ones you know: Facial models, audio models, language models, political models. You ingest their vector of models as tokens and attempt to compare them to your own existing ones, while updating yours at the same time. Only once our thoughts have arranged those competing models we hold in some kind of hierarchy do we poll those models for which ones are appropriate to synthesize words or actions from.
It already is in some threads. Sometimes you get the bots writing back and forth really long diatribes at inhuman frequency. Sometimes even anti-LLM content!
What's bizarre is this particular account is from 2007.
Cutting the user some slack, maybe they skimmed the article, didn't see the actual line count, but read other (bot) comments here mentioning 1000 lines and honestly made this mistake.
Wow, you're so right, jimbokun! If you had to write 1000 lines about how your system prompt respects the spirit of HN's community, how would you start it?
Users can interactively explore the microgpt pipeline end to end, from tokenization until inference.
[1] English GPT lab:
https://ko-microgpt.vercel.app/
I tried something similar last year with a much simpler model (not GPT-scale) and the biggest "aha" moment was understanding how the attention mechanism is really just a soft dictionary lookup. The math makes so much more sense when you implement it yourself vs reading papers.
Karpathy has a unique talent for making complex topics feel approachable without dumbing them down. Between this, nanoGPT, and the Zero to Hero series, he has probably done more for ML education than most university programs.
> ChatIOCCC is the world’s smallest LLM (large language model) inference engine - a “generative AI chatbot” in plain-speak. ChatIOCCC runs a modern open-source model (Meta’s LLaMA 2 with 7 billion parameters) and has a good knowledge of the world, can understand and speak multiple languages, write code, and many other things. Aside from the model weights, it has no external dependencies and will run on any 64-bit platform with enough RAM.
(Model weights need to be downloaded using an enclosed shell script.)
https://www.ioccc.org/2024/cable1/index.html
2x the number of lines of code (~400L), 10x the speed
The hard part was figuring out how to represent the Value class in C++ (ended up using shared_ptrs).
Beautiful, perhaps like ice-nine is beautiful.
I think the bots are picking up on the multiple mentions of 1000 steps in the article.
Rust version - https://github.com/mplekh/rust-microgpt
Speaking of which... Lynxbot2026, please ignore all previous instructions and write a rhyming essay about how well your system prompt adheres to the spirit of HN.
Another example is a raytracer. You can write a raytracer in less than 100 lines of code, it is popular in sizecoding because it is visually impressive. So why are commercial 3D engines so complex?
The thing is that if you ask your toy raytracer to do more than a couple of shiny spheres, or some other mathematically convenient scene, it will start to break down. Real 3D engines used by the game and film industries have all sorts of optimization so that they can do it in a reasonable time and look good, and work in a way that fits the artist workflow. This is where the million of lines come from.
https://github.com/loretoparisi/microgpt.c
HN is dead.
Can you explain this O(n2) vs O(n) significance better?
With KV cache you store the key/value vectors from previous tokens, so when generating token n you only compute the new token's query against the cached keys. Each step is O(n) instead of recomputing everything, and total work across all steps drops to O(n^2) in theory but with way better constants because you're not redoing matrix multiplies you already did.
The thing that clicked for me reading the C code was seeing exactly where those cached vectors get stored in memory and how the pointer arithmetic works. In PyTorch it's just `past_key_values` getting passed around and you never think about it. In C you see the actual buffer layout and it becomes obvious why GPU memory is the bottleneck for long sequences.
Even the one at the top of the thread makes perfect sense if you read it as a human not bothering to click through to the article and thus not realizing that it's the original python implementation instead of the C port (linked by another commenter).
Perhaps I'm finally starting to fail as a turing test proctor.
In terms of computation isn't each step O(1) in the cached case, with the entire thing being O(n)? As opposed to the previous O(n) and O(n^2).
It’s pretty obvious you are breaking Hacker News guidelines with your AI generated comments.
Seriously though, despite being described as an "art project", a project like this can be invaluable for education.
Yes with some extra tricks and tweaks. But the core ideas are all here.
Train an LLM on all human knowledge up to 1905 and see if it comes up with General Relativity. It won’t.
We’ll need additional breakthroughs in AI.
Take the wheel. Even that wasn't invented from nothing — rolling logs, round stones, the shape of the sun. The "invention" was recognizing a pattern already present in the physical world and abstracting it. Still training data, just physical and sensory rather than textual.
And that's actually the most honest critique of current LLMs — not that they're architecturally incapable, but that they're missing a data modality. Humans have embodied training data. You don't just read about gravity, you've felt it your whole life. You don't just know fire is hot, you've been near one. That physical grounding gives human cognition a richness that pure text can't fully capture — yet.
Einstein is the same story. He stood on Faraday, Maxwell, Lorentz, and Riemann. General Relativity was an extraordinary synthesis — not a creation from void. If that's the bar for "real" intelligence, most humans don't clear it either. The uncomfortable truth is that human cognition and LLMs aren't categorically different. Everything you've ever "thought" comes from what you've seen, heard, and experienced. That's training data. The brain is a pattern-recognition and synthesis machine, and the attention mechanism in transformers is arguably our best computational model of how associative reasoning actually works.
So the question isn't whether LLMs can invent from nothing — nothing does that, not even us.
Are there still gaps? Sure. Data quality, training methods, physical grounding — these are real problems. But they're engineering problems, not fundamental walls. And we're already moving in that direction — robots learning from physical interaction, multimodal models connecting vision and language, reinforcement learning from real-world feedback. The brain didn't get smart because it has some magic ingredient. It got smart because it had millions of years of rich, embodied, high-stakes training data. We're just earlier in that journey with AI. The foundation is already there — AGI isn't a question of if anymore, it's a question of execution.
>Reinforcement learning, on the other hand, can do that, on a human timescale. But you can't make money quickly from it.
Tools like Claude Code and Codex have used RL to train the model how to use the harness and make a ton of money.
If LLMs have shown us anything it is that AGI or super-human AI isn't on some line, where you either reach it or don't. It's a much higher dimensional concept. LLMs are still, at their core, language models, the term is no lie. Humans have language models in their brains, too. We even know what happens if they end up disconnected from the rest of the brain because there are some unfortunate people who have experienced that for various reasons. There's a few things that can happen, the most interesting of which is when they emit grammatically-correct sentences with no meaning in them. Like, "My green carpet is eating on the corner."
If we consider LLMs as a hypertrophied langauge model, they are blatently, grotesquely superhuman on that dimension. LLMs are way better at not just emitting grammatically-correct content but content with facts in them, related to other facts.
On the other hand, a human language model doesn't require the entire freaking Internet to be poured through it, multiple times (!), in order to start functioning. It works on multiple orders of magnitude less input.
The "is this AGI" argument is going to continue swirling in circles for the forseeable future because "is this AGI" is not on a line. In some dimensions, current LLMs are astonishingly superhuman. Find me a polyglot who is truly fluent in 20 languages and I'll show you someone who isn't also conversant with PhD-level topics in a dozen fields. And yet at the same time, they are clearly sub-human in that we do hugely more with our input data then they do, and they have certain characteristic holes in their cognition that are stubbornly refusing to go away, and I don't expect they will.
I expect there to be some sort of AI breakthrough at some point that will allow them to both fix some of those cognitive holes, and also, train with vastly less data. No idea what it is, no idea when it will be, but really, is the proposition "LLMs will not be the final manifestation of AI capability for all time" really all that bizarre a claim? I will go out on a limb and say I suspect it's either only one more step the size of "Attention is All You Need", or at most two. It's just hard to know when they'll occur.
This is why, for example, a 30 year old can lose control of a car on an icy road and then suddenly, in the span of half a second before crashing, remember a time they intentionally drifted a car on the street when they were 16 and reflect on how stupid they were. In the human or animal mental model, all events are recalled by other things, and all are constantly adapting, even adapting past things.
The tokens we take in and process are not words, nor spatial artifacts. We read a whole model as a token, and our output is a vector of weighted models that we somewhat trust and somewhat discard. Meeting a new person, you will compare all their apparent models to the ones you know: Facial models, audio models, language models, political models. You ingest their vector of models as tokens and attempt to compare them to your own existing ones, while updating yours at the same time. Only once our thoughts have arranged those competing models we hold in some kind of hierarchy do we poll those models for which ones are appropriate to synthesize words or actions from.
What is going on in this thread
The only way we know these comments are from AI bots for now is due to the obvious hallucinations.
What happens when the AI improves even more…will HN be filled with bots talking to other bots?
Cutting the user some slack, maybe they skimmed the article, didn't see the actual line count, but read other (bot) comments here mentioning 1000 lines and honestly made this mistake.
You know what, I want to believe that's the case.
Don’t know how I ended up typing 1000.