According to Andrej Karpathy (@karpathy) on Twitter, nanochat is a newly released open-source project that provides a minimal, from-scratch, full-stack training and inference pipeline for building a ChatGPT-like large language model (LLM). Unlike Karpathy's previous nanoGPT, which only handled pretraining, nanochat enables users to train a transformer-based LLM from pretraining through supervised fine-tuning (SFT) and reinforcement learning (RL), all in a single, dependency-minimal codebase. The pipeline includes a Rust-based tokenizer, training on FineWeb data, midtraining with SmolTalk conversations, and evaluation across benchmarks such as ARC-Easy, MMLU, GSM8K, and HumanEval. Notably, users can deploy and interact with their own LLM via a web UI or CLI after as little as four hours of training on a cloud GPU, making advanced LLM development more accessible and affordable for researchers and developers. This release lowers the entry barrier for custom LLM experimentation, offering business opportunities in rapid prototyping, education, and research tools within the AI industry (source: @karpathy).