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Deep Dive into LLMs like ChatGPT

Andrej Karpathy

3:31:24 · 2025

YouTube

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Overview

Andrej Karpathy's three-hour-plus general-audience deep dive into how ChatGPT-style LLMs are built, covering the full training stack from pretraining to post-training. It also gives mental models for their quirks, like hallucination, and how to use them well.

Why HN discusses it

HN's most frequent recommendation for a clear, approachable foundation in how LLMs work without heavy math.

Before you watch

No model-training experience is required for a conceptual first pass. This three-and-a-half-hour video suits learners who want a broad account of LLMs before writing code.

A way to study this video

Split the video into several sessions. After each section, distinguish training from inference and write one question about what the model can and cannot learn. Use the shorter introduction if you need an orientation first.

Follow the Andrej Karpathy learning guide · Original Zero to Hero course

LLMs & generative AI · Machine learning & deep learning

HN comments

18 collected comments

Newest first

QuantumNomad_Reference

In discussion: Show HN: How LLMs Work – Interactive visual guide based on Karpathy's lecture

I agreed when I read your comment, but that turned out to be almost directly from the video [VIDEO] From around the 2:20 mark he says: “[…] actually ends up being only about 44 TB of disk space. You can get a USB stick for like a TB very easily, or I think this could fit on a single hard drive almost today” So it’s just slightly altered from what was said in the original video. And the LLM rewritten version of it…

etothetStrong recommendation

In discussion: Microgpt

Even if you have some basic understanding of how LLMs work, I highly recommend Karpathy’s intro to LLMs videos on YouTube. - [VIDEO] - [LINK]

npalliRecommendation

In discussion: Neural Networks: Zero to Hero

This is a good resource, however for about 99.99% of people, you are most likely to just use a foundation model like ChatGPT, Claude, Gemini etc. so this knowledge/training will get you neither here or there. I would suggest you look into another Karpathy's video -- Deep Dive into LLMs like ChatGPT. [VIDEO]

CamperBob2Reference

In discussion: Using secondary school maths to demystify AI

That's post-training No, it is not. Read the paper. They are discussing an emergent property of the context itself: "For all tasks, GPT-3 is applied without any gradient updates or fine-tuning, with tasks and few-shot demonstrations specified purely via text interaction with the model." I'm talking about tasks like multiplying two 4-digit numbers (let's say 8-digit, just to be safe, for reasoning models), which 5th…

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