karpathy / build-nanogpt

Video+code lecture on building nanoGPT from scratch

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build nanoGPT

This repo holds the from-scratch reproduction of nanoGPT. The git commits were specifically kept step by step and clean so that one can easily walk through the git commit history to see it built slowly. Additionally, there is an accompnaying video lecture on YouTube where you can see me introduce each commit and explain the pieces along the way.

We basically start from an empty file and work our way to a reproduction of the GPT-2 (124M) model. If you have more patience or money, the code can also reproduce the GPT-3 models. While the GPT-2 (124M) model probably trained for quite some time back in the day (2019, ~5 years ago), today, reproducing it is a matter of ~1hr and ~$10. You'll need a cloud GPU box if you don't have enough, for that I recommend Lambda.

Note that GPT-2 and GPT-3 and both simple language models, trained on internet documents, and all they do is "dream" internet documents. So this repo/video this does not cover Chat finetuning, and you can't talk to it like you can talk to ChatGPT. The finetuning process (while quite simple conceptually - SFT is just about swapping out the dataset and continuing the training) comes after this part and will be covered at a later time. For now this is the kind of stuff that the 124M model says if you prompt it with "Hello, I'm a language model," after 10B tokens of training:

Hello, I'm a language model, and my goal is to make English as easy and fun as possible for everyone, and to find out the different grammar rules
Hello, I'm a language model, so the next time I go, I'll just say, I like this stuff.
Hello, I'm a language model, and the question is, what should I do if I want to be a teacher?
Hello, I'm a language model, and I'm an English person. In languages, "speak" is really speaking. Because for most people, there's

And after 40B tokens of training:

Hello, I'm a language model, a model of computer science, and it's a way (in mathematics) to program computer programs to do things like write
Hello, I'm a language model, not a human. This means that I believe in my language model, as I have no experience with it yet.
Hello, I'm a language model, but I'm talking about data. You've got to create an array of data: you've got to create that.
Hello, I'm a language model, and all of this is about modeling and learning Python. I'm very good in syntax, however I struggle with Python due

Lol. Anyway, once the video comes out, this will also be a place for FAQ, and a place for fixes and errata, of which I am sure there will be a number :)

For discussions and questions, please use Discussions tab, and for faster communication, have a look at my Zero To Hero Discord, channel #nanoGPT:


Let's reproduce GPT-2 (124M) YouTube lecture


Minor cleanup, we forgot to delete register_buffer of the bias once we switched to flash attention, fixed with a recent PR.

Earlier version of PyTorch may have difficulty converting from uint16 to long. Inside load_tokens, we added npt = npt.astype(np.int32) to use numpy to convert uint16 to int32 before converting to torch tensor and then converting to long.

The torch.autocast function takes an arg device_type, to which I tried to stubbornly just pass device hoping it works ok, but PyTorch actually really wants just the type and creates errors in some version of PyTorch. So we want e.g. the device cuda:3 to get stripped to cuda. Currently, device mps (Apple Silicon) would become device_type CPU, I'm not 100% sure this is the intended PyTorch way.





Video+code lecture on building nanoGPT from scratch


Language:Python 75.6%Language:Jupyter Notebook 24.4%