tl;dr: Karpathy, frustrated by YouTube's "enshittified" recommendations, used Claude Opus 5.5 to build HackerTube.org—a YouTube clone populated with 6,454 videos recommended across 40K Hacker News comments from 2007-2026, organized into 150 topics with custom ForYou recommendations and no user accounts. The entire project took ~2 hours, with Karpathy only manually handling the API key, VPS setup, and domain purchase while Claude Code did the rest, including deployment and hardening.