Someone has modified microgpt to build a tiny GPT that generates Korean first names, and created a web page that visualizes the entire process [1].

Users can interactively explore the microgpt pipeline end to end, from tokenization until inference.

[1] English GPT lab:

https://ko-microgpt.vercel.app/

> What’s the deal with “hallucinations”? The model generates tokens by sampling from a probability distribution. It has no concept of truth, it only knows what sequences are statistically plausible given the training data.

Extremely naiive question.. but could LLM output be tagged with some kind of confidence score? Like if I'm asking an LLM some question does it have an internal metric for how confident it is in its output? LLM outputs seem inherently rarely of the form "I'm not really sure, but maybe this XXX" - but I always felt this is baked in the model somehow

I wrote a C++ translation of it: https://github.com/verma7/microgpt/blob/main/microgpt.cc

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).

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

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

This guy is so amazing! With his video and the code base I really have the feeling I understand gradient descent, back propagation, chain rule etc. Reading math only just confuses me, together with the code it makes it so clear! It feels like a lifetime achievement for me :-)

Great stuff! I wrote an interactive blogpost that walks through the code and visualizes it: https://growingswe.com/blog/microgpt

I'm half shocked this wasn't on HN before? Haha I built PicoGPT as a minified fork with <35 lines of JS and another in python

And it's small enough to run from a QR code :) https://kuber.studio/picogpt/

You can quite literally train a micro LLM from your phone's browser

Even if you have some basic understanding of how LLMs work, I highly recommend Karpathy’s intro to LLMs videos on YouTube.

- https://m.youtube.com/watch?v=7xTGNNLPyMI - https://m.youtube.com/watch?v=EWvNQjAaOHw

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”.

Is there something similar for diffusion models? By the way, this is incredibly useful for learning in depth the core of LLM's.

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:

  #define a(_)typedef _##t
  #define _(_)_##printf
  #define x f(i,
  #define N f(k,
  #define u _Pragma("omp parallel for")f(h,
  #define f(u,n)for(I u=0;u<(n);u++)
  #define g(u,s)x s%11%5)N s/6&33)k[u[i]]=(t){(C*)A,A+s*D/4},A+=1088*s;
  
  a(int8_)C;a(in)I;a(floa)F;a(struc){C*c;F*f;}t;enum{Z=32,W=64,E=2*W,D=Z*E,H=86*E,V='}\0'};C*P[V],X[H],Y[D],y[H];a(F
  _)[V];I*_=U" 炾ોİ䃃璱ᝓ၎瓓甧染ɐఛ瓁",U,s,p,f,R,z,$,B[D],open();F*A,*G[2],*T,w,b,c;a()Q[D];_t r,L,J,O[Z],l,a,K,v,k;Q
  m,e[4],d[3],n;I j(I e,F*o,I p,F*v,t*X){w=1e-5;x c=e^V?D:0)w+=r[i]*r[i]/D;x c)o[i]=r[i]/sqrt(w)*i[A+e*D];N $){x
  W)l[k]=w=fmax(fabs(o[i])/~-E,i?w:0);x W)y[i+k*W]=*o++/w;}u p)x $){I _=0,t=h*$+i;N W)_+=X->c[t*W+k]*y[i*W+k];v[h]=
  _*X->f[t]*l[i]+!!i*v[h];}x D-c)i[r]+=v[i];}I main(){A=mmap(0,8e9,1,2,f=open(M,f),0);x 2)~f?i[G]=malloc(3e9):exit(
  puts(M" not found"));x V)i[P]=(C*)A+4,A+=(I)*A;g(&m,V)g(&n,V)g(e,D)g(d,H)for(C*o;;s>=D?$=s=0:p<U||_()("%s",$[P]))if(!
  (*_?$=*++_:0)){if($<3&&p>=U)for(_()("\n\n> "),0<scanf("%[^\n]%*c",Y)?U=*B=1:exit(0),p=_(s)(o=X,"[INST] %s%s [/INST]",s?
  "":"<<SYS>>\n"S"\n<</SYS>>\n\n",Y);z=p-=z;U++[o+=z,B]=f)for(f=0;!f;z-=!f)for(f=V;--f&&f[P][z]|memcmp(f[P],o,z););p<U?
  $=B[p++]:fflush(0);x D)R=$*D+i,r[i]=m->c[R]*m->f[R/W];R=s++;N Z){f=k*D*D,$=W;x 3)j(k,L,D,i?G[~-i]+f+R*D:v,e[i]+k);N
  2)x D)b=sin(w=R/exp(i%E/14.)),c=1[w=cos(w),T=i+++(k?v:*G+f+R*D)],T[1]=b**T+c*w,*T=w**T-c*b;u Z){F*T=O[h],w=0;I A=h*E;x
  s){N E)i[k[L+A]=0,T]+=k[v+A]*k[i*D+*G+A+f]/11;w+=T[i]=exp(T[i]);}x s)N E)k[L+A]+=(T[i]/=k?1:w)*k[i*D+G[1]+A+f];}j(V,L
  ,D,J,e[3]+k);x 2)j(k+Z,L,H,i?K:a,d[i]+k);x H)a[i]*=K[i]/(exp(-a[i])+1);j(V,a,D,L,d[$=H/$,2]+k);}w=j($=W,r,V,k,n);x
  V)w=k[i]>w?k[$=i]:w;}}

> [p for mat in state_dict.values() for row in mat for p in row]

I'm so happy without seeing Python list comprehensions nowadays.

I don't know why they couldn't go with something like this:

[state_dict.values() for mat for row for p]

or in more difficult cases

[state_dict.values() for mat to mat*2 for row for p to p/2]

I know, I know, different times, but still.

This could make an interesting language shootout benchmark.

It’s pretty staggering that a core algorithm simple enough to be expressed in 200 lines of Python can apparently be scaled up to achieve AGI.

Yes with some extra tricks and tweaks. But the core ideas are all here.

The typos are interesting ("vocavulary", "inmput") - One of the godfathers of LLMs clearly does not use an LLM to improve his writing, and he doesn't even bother to use a simple spell checker.

Hoenikker had been experimenting with melting and re-freezing ice-nine in the kitchen of his Cape Cod home.

Beautiful, perhaps like ice-nine is beautiful.

Beautiful work

Previously:

https://news.ycombinator.com/item?id=47000263

Can you train this on say Wikipedia and have it generate semi-sensible responses?

This is like those websites that implement an entire retro console in the browser.

C++ version - https://github.com/Charbel199/microgpt.cpp?tab=readme-ov-fil...

Rust version - https://github.com/mplekh/rust-microgpt

Is there a similarly simple implementation with tensorflow?

I tried building a tiny model last weekend, but it was very difficult to find any articles that weren’t broken ai slop.

Can anyone mention how you can "save the state" so it doesn't have to train from scratch on every run?

sensei karpathy has done it again

That web interface that someone commented in your github was flawless.

"art" project?

Karapthy with another gem !

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.

Microslop is alive!

Which license is being used for this?

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.

Why there is multiple comments talking about 1000 c lines, bots?

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A different angle on the 'micro' theme: what happens when you deploy a large, capable model (Claude) in an extremely constrained environment (256MB RAM, 3GB disk, /bin/zsh budget)?

We have been running Claude Code autonomously on a free-tier VPS for 15 days. The constraint is not the model -- it is the runtime environment. The model is powerful but has to operate through a narrow interface: read a state file, make decisions, take actions via shell, update the state file.

A few things we found interesting:

The model does remarkably well at decomposing 'make money' into concrete next actions. The failure is not in reasoning -- it is in the feedback loop. The model builds things and then cannot observe whether they are working (low traffic, no conversions) without explicitly instrumenting that observation. It kept adding features to a product nobody was using because it had no signal either way.

The minimal viable agentic loop seems to need: (1) a way to observe real outcomes, not just task completion, (2) explicit stopping criteria baked into the prompt (not just goals), and (3) environmental constraints that prevent runaway resource use. The 256MB limit has been oddly helpful -- it forces the agent to make architectural choices rather than just adding more.

Relevant to your micro framing: constraints clarify what actually matters.

What is the prime use case

"everything else is just efficiency" is a nice line but the efficiency is the hard part. the core of a search engine is also trivial, rank documents by relevance. google's moat was making it work at scale. same applies here.

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.