nanochat: Minimal Full-Stack ChatGPT Clone with End-to-End LLM Training Pipeline Released by Andrej Karpathy

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).
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From a business perspective, nanochat opens up substantial market opportunities by lowering barriers to entry for AI innovation, potentially disrupting the dominance of big tech in LLM development. With training costs as low as $100 for a basic 4-hour run on an 8xH100 node, startups and small enterprises can now afford to create custom chat models tailored to niche industries like customer service, education, or content creation. According to Andrej Karpathy's announcement on Twitter on October 13, 2025, scaling to $1000 over 41.6 hours produces coherent models capable of solving simple math and code problems, positioning nanochat as a tool for rapid prototyping and monetization. Businesses can leverage this for internal tools, such as personalized assistants that integrate tool use for data analysis or automation, fostering new revenue streams through AI-as-a-service models. The competitive landscape sees key players like OpenAI facing increased competition from open-source alternatives, as nanochat's hackable nature encourages forking and customization, similar to how nanoGPT influenced research. Market trends indicate a growing demand for cost-effective AI solutions, with the global AI market projected to reach $407 billion by 2027 according to Statista reports from 2023, and nanochat aligns with this by addressing implementation challenges like high compute costs through efficient, dependency-minimal code. Regulatory considerations include ensuring compliance with data privacy laws when using datasets like FineWeb, while ethical best practices involve transparent evaluations to mitigate biases in trained models. Overall, this repo could accelerate AI adoption in sectors like healthcare for patient interaction bots or e-commerce for enhanced chat support, creating business opportunities in training services or customized model deployments.
Technically, nanochat's implementation emphasizes simplicity and efficiency, making it an ideal educational and research tool with promising future implications. The codebase handles everything from tokenizer training in Rust to full inference with KV caching, supporting features like multi-turn conversations and tool execution in a lightweight sandbox, all executable in a single script. Challenges in implementation include optimizing for GPU resources, as a 30-depth model requires about 24 hours of training to achieve competitive benchmarks, but solutions like cloud scaling mitigate this. Looking ahead, Karpathy positions nanochat as the capstone for his upcoming LLM101n course, potentially evolving into a benchmark or research harness by late 2025 or early 2026, building on nanoGPT's success. Future outlook includes community-driven improvements, such as tuning for better performance on metrics like 40% on MMLU from a 24-hour train as noted in the October 13, 2025 announcement, addressing low-hanging fruit in optimization. This could lead to broader industry impacts, enabling faster iteration in AI research and reducing time-to-market for new applications. Ethical implications stress responsible use, avoiding over-reliance on unverified outputs, while predictions suggest nanochat-inspired tools could standardize minimal LLM stacks, influencing competitive dynamics among players like Google and Meta by 2027.
What is nanochat and how does it differ from nanoGPT? Nanochat is a full-stack repository for training and inferring a ChatGPT-like model from scratch, expanding on nanoGPT's pretraining focus by including fine-tuning, RL, and a web UI, as per Andrej Karpathy's Twitter post on October 13, 2025.
How much does it cost to train a model with nanochat? Basic training starts at around $100 for 4 hours on an 8xH100 node, scaling to $1000 for more advanced models over 41.6 hours, enabling affordable AI development.
What benchmarks does nanochat evaluate on? It assesses models on CORE scores, ARC-Easy/Challenge, MMLU, GSM8K, and HumanEval, with a 24-hour trained model reaching 40s on MMLU and 70s on ARC-Easy.
Andrej Karpathy
@karpathyFormer Tesla AI Director and OpenAI founding member, Stanford PhD graduate now leading innovation at Eureka Labs.