GPT & OpenAI: The Complete Developer Guide
Everything about OpenAI's GPT models — GPT-4o, GPT-5, API usage, function calling, assistants API, and building AI applications with OpenAI.
GPT Model Family
OpenAI's GPT (Generative Pre-trained Transformer) family powers ChatGPT and is the most widely used AI model platform:
•GPT-4o — flagship multimodal model (text, image, audio) •GPT-4o mini — fast and cheap for simple tasks •o1 / o3 — reasoning models for math, science, coding •GPT-5 — next-gen model (announced 2026)
Building with the OpenAI API
Key APIs for developers: •Chat Completions — core text generation •Function Calling — structured tool use •Assistants API — stateful agents with tools and files •Embeddings — text-to-vector for search •Fine-tuning — customize models on your data •DALL-E — image generation •Whisper — speech-to-text
GPT vs Claude vs Gemini
GPT-4o: Best ecosystem (thousands of plugins), strong all-rounder, best for image generation (DALL-E), most third-party integrations.
Claude Sonnet: Better at coding, stronger instruction following, better safety.
Gemini Pro: Larger context (1M+), better multimodal (video), Google Workspace integration.
See our detailed comparison: ChatGPT vs Claude vs Gemini
Learn to build with GPT and Claude in our training
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Frequently Asked Questions
Is GPT-5 available?↓
GPT-5 has been announced by OpenAI for 2026 release. Check OpenAI's blog for the latest status. GPT-4o remains the current flagship model.
OpenAI API vs ChatGPT — what's the difference?↓
ChatGPT is the consumer product (web/mobile app). The OpenAI API lets developers integrate GPT into their own applications programmatically. Same models, different interface.