whatisgithub

What is llama2.c?

karpathy/llama2.c — explained in plain English

Analysis updated 2026-06-21

19,500CAudience · researcherComplexity · 3/5Setup · moderate

In one sentence

llama2.c runs Meta's Llama 2 AI language model using a single 700-line C file with zero dependencies, ideal for learning how AI inference works or running a tiny local text generator without Python.

Mindmap

mindmap
  root((llama2.c))
    What it does
      Run Llama 2 AI
      Single C file
      Generate text
    Tech stack
      C inference
      Python training
      PyTorch
    Models
      TinyLlama 15M
      TinyLlama 110M
      Meta Llama 2
    Use cases
      Learn AI internals
      Local text generation
      Custom model training
Click or tap to explore — scroll the page freely

Code map

Detail Auto

An interactive map of this repo's files and how they connect — its source is parsed live in your browser. Click Visualize to build it.

filefunction / class

What do people build with it?

USE CASE 1

Run a tiny local AI that generates short stories or text completions entirely offline, without Python or any AI framework installed.

USE CASE 2

Learn how large language model inference works at a low level by reading and modifying a single readable C file.

USE CASE 3

Train a small custom language model from scratch using the included PyTorch code, then run it with the C inference engine.

What is it built with?

CPythonPyTorch

How does it compare?

karpathy/llama2.cish-app/ishawesome-harmonyos/harmonyos
Stars19,50019,84719,874
LanguageCCC
Setup difficultymoderatehardeasy
Complexity3/55/51/5
Audienceresearcherdeveloperdeveloper

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · moderate Time to first run · 30min

Needs a C compiler for inference, PyTorch is required only if training custom models from scratch.

So what is it?

llama2.c is a minimalist project that lets you run Llama 2, Meta's large language model AI, using a single file of plain C code with no external dependencies. The problem it solves is making AI language models approachable for learning and experimentation: instead of a huge complex codebase, you get one readable 700-line file that handles the inference (the "run the AI" part), plus PyTorch code for training smaller versions from scratch. The way it works is that you either download one of the pre-trained "TinyLlamas" (small models trained on short stories, ranging from 15M to 110M parameters) or export Meta's official Llama 2 weights into the project's format. You then compile and run the C file, which reads the model and generates text. It runs surprisingly fast, around 110 tokens per second on an M1 MacBook Air for the small models. You can give it a text prompt and it will continue the story or answer in kind. You'd use this if you want to understand how AI language models work at a low level, run a tiny AI locally without Python or heavy frameworks, or just experiment with text generation for educational purposes. The tech stack is C for inference, Python and PyTorch for training.

Copy-paste prompts

Prompt 1
I cloned karpathy/llama2.c and compiled run.c. Help me write a Python script using the included training code to train a small model on my own text dataset and export the weights for the C runner.
Prompt 2
I want to understand transformer model inference. Walk me through karpathy/llama2.c's run.c file section by section and explain what each part does in plain English.
Prompt 3
Using karpathy/llama2.c, show me the exact shell commands to download a pre-trained TinyLlama checkpoint and generate text from a custom prompt.
Prompt 4
How do I export Meta's official Llama 2 weights into the checkpoint format that karpathy/llama2.c expects, and what are the hardware requirements?

Frequently asked questions

What is llama2.c?

llama2.c runs Meta's Llama 2 AI language model using a single 700-line C file with zero dependencies, ideal for learning how AI inference works or running a tiny local text generator without Python.

What language is llama2.c written in?

Mainly C. The stack also includes C, Python, PyTorch.

How hard is llama2.c to set up?

Setup difficulty is rated moderate, with roughly 30min to a first successful run.

Who is llama2.c for?

Mainly researcher.

Open on GitHub → Ask about another repo

This repo across BitVibe Labs

Verify against the repo before relying on details.