Karpathy Launches nanochat: Open-Source AI Chatbot Clone

OpenAI co-founder and Eureka Labs founder, Andrej Karpathy, has released nanochat, an open-source project that provides a full-stack training and inference pipeline for a simple ChatGPT-style model. The repository follows his earlier project, nanoGPT, which focused only on pretraining. Link to the GitHub repository.

In a post on X, Karpathy said, “You boot up a cloud GPU box, run a single script and in as little as 4 hours later you can talk to your own LLM in a ChatGPT-like web UI.” The repo consists of about 8,000 lines of code and covers the entire pipeline. It includes tokeniser training in Rust and pretraining a Transformer LLM on FineWeb. The pipeline also handles mid-training on user-assistant conversations and multiple-choice questions, supervised fine-tuning (SFT), and optional reinforcement learning (RL) with GRPO.

Finally, it supports efficient inference with KV caching. Users can interact with the model through a command-line interface or a web UI, and the system generates a markdown report summarising performance. Karpathy explained that the models can be trained at different scales depending on time and cost.

A small ChatGPT clone can be trained for around $100 in roughly 4 hours on an 8×H100 GPU node, allowing basic interaction. Training for about 12 hours enables the model to surpass the GPT-2 CORE benchmark.