Post 1 was Python variables. Post 100 is GPT-4. You've come from writing your first for loop to understanding transformer architectures, building neural networks from scratch, fine-tuning LLMs with LoRA, building RAG pipelines, and creating chatbots with memory. This final post puts it all together. The OpenAI API is how most people actually ship AI products. Chat completions, function calling, streaming, vision, embeddings. Everything you need to build something real. Let's finish strong. What You'll Learn Here API setup and authentication Chat completions: the core pattern System prompts: controlling model behavior Function calling: giving LLMs tools Streaming: responses that appear word by word Vision: analyzing images with GPT-4V Embeddings via API: fast, high quality Token counting and cost management Rate limits and error handling A complete project: an AI assistant with tools Setup pip install openai tiktoken Enter fullscreen mode Exit fullscreen mode import openai import os # Set your API key #…