What Is GPT-1? The Original GPT, Explained
GPT-1 is the first model in OpenAI's GPT family. It came out in June 2018, more than four years before ChatGPT. It was small by today's standards, but it introduced the recipe every GPT model since has followed: pre-train a large Transformer on huge amounts of text, then adapt it to specific tasks.
GPT-1 at a glance
| Released | June 2018, by OpenAI |
|---|---|
| Paper | "Improving Language Understanding by Generative Pre-Training", by Alec Radford, Karthik Narasimhan, Tim Salimans and Ilya Sutskever |
| Size | ~117 million parameters |
| Architecture | 12-layer, decoder-only Transformer (768-wide, 12 attention heads) |
| Context window | 512 tokens |
| Training data | BooksCorpus, about 7,000 unpublished books |
| Could it chat? | No. It was a research model, not a chatbot |
What did "GPT" mean, and why did it matter?
GPT stands for Generative Pre-trained Transformer:
- Generative: it learns by predicting the next word in a text.
- Pre-trained: it first learns general language from a big pile of unlabeled text, before being taught any specific job.
- Transformer: the neural-network design (from Google's 2017 "Attention Is All You Need" paper) that lets the model weigh every word against every other word.
Before GPT-1, most language systems were trained from scratch for one task at a time, using expensive hand-labeled data. GPT-1 showed that one model pre-trained on raw text, then lightly fine-tuned, could beat those specialized systems. In the paper, it improved the state of the art on 9 of the 12 tasks tested, including question answering, textual entailment and sentence similarity.
Books were a deliberate choice of training data: long, continuous stories teach a model to track context across many sentences, rather than just guessing the next word from a short phrase.
From GPT-1 to ChatGPT: the timeline
| Model | Year | What changed |
|---|---|---|
| GPT-1 | 2018 | ~117M parameters. Proved the pre-train, then fine-tune approach. |
| GPT-2 | 2019 | 1.5B parameters. Wrote surprisingly fluent text; OpenAI initially held back the full model over misuse concerns. |
| GPT-3 | 2020 | 175B parameters. Could do new tasks from just a few examples in the prompt, with no fine-tuning ("few-shot learning"). |
| ChatGPT (GPT-3.5) | Nov 2022 | The first ChatGPT: a GPT-3.5 model tuned for conversation with human feedback (RLHF). |
| GPT-4 | 2023 | Big jump in reasoning; accepts images as well as text. |
| GPT-4o | 2024 | Faster, natively multimodal (text, images, voice). |
| GPT-5 | 2025 | Unified model that decides how long to "think" before answering. |
The core idea is still GPT-1's. Each step made the model much bigger, trained it on much more data, and added better ways to align it with what people actually want.
Is there a "ChatGPT 1" or "ChatGPT 1.5"?
No. OpenAI has never released anything called ChatGPT 1 or ChatGPT 1.5. The confusion usually comes from one of these:
- GPT-1, the 2018 research model described on this page, which had no chat interface.
- GPT-3.5, the model behind the original ChatGPT launch in November 2022, which is effectively "ChatGPT version 1".
- Gemini 1.5, a Google model whose "1.5" version number often gets mixed up with ChatGPT.
Can you still use GPT-1?
Yes. OpenAI published GPT-1's weights, and you can run it for free through Hugging Face (model name openai-gpt). Expect short, often incoherent output. It is interesting for learning how language models work, not for real tasks. For anything practical, use a current model in ChatGPT, and give it a well-structured prompt.
Why this matters for your prompts
GPT-1 needed fine-tuning to do a new task. Modern models learn the task from your prompt. That makes the prompt the most important input you control: clear context, a specific goal and constraints get dramatically better answers. That is what ChatGPT1 is for:
- Build a prompt in 30 seconds with our free prompt builder.
- Browse the prompt library for tested, copy-paste prompts.
FAQ
What is GPT-1?
GPT-1 is the first Generative Pre-trained Transformer model, released by OpenAI in June 2018. It had about 117 million parameters and showed that pre-training a language model on lots of unlabeled text, then fine-tuning it, beats training task-specific models from scratch.
Is there a ChatGPT 1 or ChatGPT 1.5?
No. OpenAI never released products called "ChatGPT 1" or "ChatGPT 1.5". ChatGPT launched in November 2022 running on a GPT-3.5 model. People searching "ChatGPT 1.5" usually mean GPT-3.5, or are mixing it up with Google's Gemini 1.5.
Can I still use GPT-1?
Yes, for experiments. OpenAI released GPT-1's weights, and they are available on Hugging Face as "openai-gpt". It is far weaker than modern models, so it is useful for learning and research, not for everyday tasks.
Is chatgpt1.org the official ChatGPT?
No. ChatGPT1 is an independent prompt library and is not affiliated with OpenAI. The official ChatGPT is at chatgpt.com. We help you write better prompts to use there.
How big is GPT-1 compared to newer models?
GPT-1 had about 117 million parameters. GPT-2 had 1.5 billion and GPT-3 had 175 billion. OpenAI has not published parameter counts for GPT-4 and later models.