GStack is an open-source toolkit built by YC President & CEO Garry Tan that turns Claude Code into an AI engineering team — with skills for office hours, design, code review, QA, and browser testing.

Use it with Claude Code or Codex or Cursor. It's free and open source: https://github.com/garrytan/gstack

In this video, Garry walks through how GStack works, starting with Office Hours, a skill modeled after real YC partner sessions that pressure-tests your idea before you write a line of code. He demos it live, going from idea through adversarial review, design mockups, and automated QA in a single session.

00:00 – AI Just Changed Coding Forever
00:09 – From YC to Building With AI
01:07 – Why AI Coding Feels So Different
02:45 – Turning AI Into a Real Team (GStack)
03:45 – Let’s Build an App Live
05:23 – The Question That Kills Most Ideas
07:13 – This Idea Just Got Way Bigger
08:38 – The “Feels Illegal” AI Hack
10:50 – Upgrading the Idea in Real Time
12:44 – Breaking + Fixing the Plan
14:25 – AI Designs the App
16:59 – The Full System Explained
18:00 – Running Multiple AI Engineers
20:00 – Shipping 10x Faster
21:20 – The Only Thing That Matters Now

Apply to Y Combinator: https://www.ycombinator.com/apply
Work at a startup: https://www.ycombinator.com/jobs

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