GPT (Generative Pre-trained Transformer)
OpenAI's LLM family — GPT-1 (2018) → GPT-2 (2019) → GPT-3 (2020) → GPT-4 (2023) → GPT-4o (2024) → o1/o3 (reasoning, 2024–2025).
Decoder-only transformer trained on "next-token prediction". GPT-3 (175 B parameters) demonstrated emergent few-shot in-context learning. GPT-4 multimodal (text + image). GPT-4o multimodal natively (text + image + audio). o1/o3 are reasoning models that produce inner CoT before answering.
ChatGPT (November 2022) took GPT mainstream — the fastest product ever to 100 million users (2 months). Available via openai.com, Azure OpenAI, the API. Competitors: Claude, Gemini, Llama, DeepSeek-R1.