The AI Stack Explained: LLM Talks, Program Walks

A first-principles breakdown of the entire AI stack in 15 minutes — from LLM to Agent. One mental model: the LLM can only output text, the program does everything else.

March 28, 2026
Harrison Guo
Video by: AI Operator
Published on YouTube: 2026-03-28
AI LLM Function Calling MCP Agent AI Architecture

LLM. Token. Context. Prompt. Function Calling. MCP. Agent. Skill — 8 concepts, 1 pattern.

An LLM can only output text. It can’t browse the web, call APIs, or take any action. The program around it does everything else. LLM talks, program walks. That loop is how the entire AI world runs.

This video peels back every layer of the AI stack from the bottom up, building a mental model that makes any new buzzword transparent.

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