ANDREJ KARPATHY, CO-FOUNDER OF OPENAI, THE MAN WHO COINED "VIBE CODING," HAS A FREE 2-HOUR LECTURE THAT BUILDS GPT FROM SCRATCH. Not a surface level explainer. Tokenization, attention, the actual Transformer architecture, built line by line on a real dataset until you have a working model. The underlying reason your token bill climbs every message in a long chat is real and worth understanding separately: each turn resends your entire conversation history, so cost compounds with every reply, not just the new message. This lecture is where that mechanism actually gets explained from the ground up. Bookmark this and give it 2 hours today.(CyrilXBT)