# GPT (Generative Pre-trained Transformer)

URL: https://softwaredictionary.org/terms/gpt
Category: AI & Machine Learning
Last updated: 2026-10-03
Pronunciation: jee-pee-TEE

In short: GPT (Generative Pre-trained Transformer) is OpenAI's family of large language models that generate text by predicting the next token.

## What is GPT?

Each word in the name describes the design. Generative: the model produces new text. Pre-trained: it first learns from a huge amount of general text before being adapted to specific uses. Transformer: it uses the transformer architecture introduced by Google researchers in 2017, whose attention mechanism lets every token look at every other token in the context.

OpenAI released GPT-1 in 2018, GPT-2 in 2019 and GPT-3 in 2020, each much larger than the last. GPT-3 showed that a big enough model could do new tasks from a few examples in the prompt. Later models were further trained on instructions and human feedback, which turned them into helpful assistants, and powered ChatGPT from November 2022 and GPT-4 in 2023.

Technically a GPT model is a decoder-only transformer. It reads the text so far as tokens and outputs a probability for every possible next token; picking one, adding it and repeating produces a reply. Developers use GPT models through OpenAI's API for chat, writing, coding, summarizing and extracting data.

A common misconception is that GPT is a synonym for every AI chatbot. GPT is OpenAI's model family; other companies build similar large language models, such as Anthropic's Claude, Google's Gemini and Meta's Llama, which share the transformer idea but are separate models.

## Key takeaways

- GPT stands for Generative Pre-trained Transformer.
- It is OpenAI's family of large language models, starting with GPT-1 in 2018.
- GPT models are decoder-only transformers that predict the next token.
- Instruction tuning and human feedback turned them into assistants like ChatGPT.
- Claude, Gemini and Llama are similar LLMs, but not GPT models.

## Example: Calling a GPT model through OpenAI's API

```python
from openai import OpenAI

client = OpenAI()  # reads OPENAI_API_KEY from the environment

response = client.responses.create(
    model="gpt-5",
    input="Explain what a REST API is in two sentences.",
)
print(response.output_text)
```

## Frequently asked questions

**What is the difference between GPT and ChatGPT?**

GPT is the model: the neural network that generates text. ChatGPT is OpenAI's chat application built on top of GPT models, with a conversation interface, memory features and tools.

**Is GPT the same as an LLM?**

GPT models are LLMs, but not every LLM is a GPT. LLM is the general category of large language models; GPT is one family within it.

**Why is it called pre-trained?**

Because the model first learns general language patterns from a large body of text, and only afterwards is fine-tuned or instructed for specific tasks. The expensive general learning happens once and is reused.

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