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Building with ChatGPT

The OpenAI Ecosystem from API to Production

The OpenAI ecosystem from API to production — master GPT-4o, o1, function calling, structured outputs, Assistants API, and the patterns for building reliable OpenAI-powered applications.

8 lessons~74 min total

Lessons are shown in recommended order. Complete them in sequence for the best experience — or jump to any lesson.

Lesson 80·9 min read

ChatGPT vs Claude vs Gemini — Choosing Your AI

The model wars have produced three serious contenders. This is not a ranking — it is a routing map. Use the right model for the right task and you will pay less and get better output than anyone blindly loyal to one provider.

Lesson 81·8 min read

The OpenAI API — Setup and Your First Call

API key, authentication, message array structure, and your first working chat completion call — everything you need to go from zero to a running OpenAI integration in under ten minutes.

Lesson 82·9 min read

GPT Models — GPT-4o, o1, o3-mini — The Routing Map

OpenAI's model lineup spans a 150× cost range. GPT-4o for speed and multimodal, o1/o3 for reasoning, mini variants for volume. Routing correctly is the difference between a $200/month AI bill and a $2,000 one for the same workload.

Lesson 83·10 min read

Function Calling and Tool Use

Function calling is the bridge between language models and the real world. The model decides which tool to invoke and what arguments to pass. Your code executes it. This is how LLMs actually do things — not just say things.

Lesson 84·9 min read

Structured Outputs — JSON Mode and Response Schemas

JSON mode gives you valid JSON. Structured outputs with strict schema enforcement give you exactly the fields you defined — no extras, no missing keys, no hallucinated properties. These are not the same thing.

Lesson 85·8 min read

Custom GPTs — No-Code AI App Builder

Custom GPTs let you ship a specialized AI app with no backend code — just instructions, uploaded files, and optional API actions. They are the fastest path from idea to deployed tool, and they have a hard ceiling that tells you exactly when to graduate to the API.

Lesson 86·10 min read

The Assistants API — Threads, Files, and Persistent Conversations

The Assistants API gives you persistent threads, built-in file search over uploaded documents, and a code interpreter — without managing conversation history yourself. It is the right layer for document Q&A and multi-turn task completion.

Lesson 87·11 min read

Building a Production OpenAI Integration

A working prototype is not a production system. Retry logic, rate limit handling, cost tracking, streaming, and a proper error taxonomy are what separate a demo from a system you can stake a product on.