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What does GPT stand for? Understanding GPT-3.5, GPT-4, GPT-4o, and more

The 'GPT' in ChatGPT is a key component of the chatbot. Here's what you need to know.
Written by Sabrina Ortiz, Editor
GPT-4 on a laptop
Sabrina Ortiz/ZDNET

OpenAI's claim to fame is its AI chatbot, ChatGPT, which has become a household name. According to a recent Pew Research Center survey, about six in 10 adults in the US are familiar with ChatGPT. Yet only a fraction likely know about the large language model (LLM) underlying the chatbot.

What does GPT stand for?

The last three letters in ChatGPT's namesake aren't just a catchy part of the name. They stand for Generative Pre-trained Transformer (GPT), a family of LLMs created by OpenAI that uses deep learning to generate human-like, conversational text.

Also: The best AI chatbots of 2024: ChatGPT and alternatives

These GPTs are used in AI chatbots because of their natural language processing abilities to understand users' text inputs and generate conversational outputs.

OpenAI's standard version of ChatGPT relies on GPT-4o to power its chatbot, which previously relied on GPT-3.5. ChatGPT Plus also uses GPT-4o. The difference is that Plus users get priority access to GPT-4o while free users will get booted back to GPT-3.5 when GPT-4o is at capacity.

Other chatbots not created by OpenAI also leverage GPT LLMs, such as Microsoft Copilot, which uses GPT-4 Turbo

What is GPT-3.5?

GPT-3.5 is an improved version of GPT-3 capable of understanding and outputting natural language prompts and generating code. GPT-3.5 powered OpenAI's free version of ChatGPT until May 2024, when it was upgraded to GPT-4o. GPT-3.5 reigned supreme as the most advanced AI model until OpenAI launched GPT-4 in March 2023. 

What is GPT-3.5 Turbo?

GPT-3.5 Turbo is a more polished version of GPT-3.5. It is available to developers through OpenAI's API. GPT-3.5 Turbo performs better on various tasks, including understanding the context of a prompt and generating higher-quality outputs.

Also: How to subscribe to ChatGPT Plus (and 5 reasons why you should)

GPT-3.5 Turbo models include gpt-3.5-turbo-1106, gpt-3.5-turbo, and gpt-3.5-turbo-16k. These models differ in their content windows and slight updates based on when they were released. Developers can select which model to use depending on their needs.

Is GPT-3.5 free?

GPT-3.5 is available in the free version of ChatGPT, which is available to the public for free. However, as seen in the image below, there is a cost if you are a developer looking to incorporate GPT-3.5 Turbo in your application.

GPT-2.5 Turbo Cost
Screenshot by Sabrina Ortiz/ZDNET

What is GPT-4?

OpenAI unveiled GPT-4 on March 14, 2023, nearly four months after the company launched ChatGPT to the public at the end of November 2022.

Also: How to use ChatGPT Plus: From web browsing to plugins

GPT-4's biggest appeal is that it is multimodal, meaning it can process voice and image inputs in addition to text prompts. GPT-4 offers many improvements over GPT 3.5, including better coding, writing, and reasoning capabilities. You can learn more about the performance comparisons below, including different benchmarks. 

Like GPT-3.5, many models fall under GPT-4, including GPT-4 Turbo, the most advanced version that powers ChatGPT Plus. 

What can GPT-4 do?

Since GPT-4 is a large multimodal model (emphasis on multimodal), it can accept both text and image inputs and output human-like text.

Also: The best AI image generators

For example, you can upload a worksheet and GPT-4 can scan it and output responses to your questions. GPT-4 can also read a graph you upload and make calculations.

GPT-4 also has more "intellectual" capabilities, outperforming GPT-3.5 in a series of simulated benchmark exams, as seen in the chart below.

ChatGPT-4 capabilities
Screenshot by Sabrina Ortiz/ZDNET

What is GPT-4 Turbo?

GPT-4 Turbo is the second-most advanced model OpenAI offers, after GPT-4o. OpenAI introduced the model in November 2023. Since then, it has undergone several upgrades, with OpenAI launching a much more improved version, gpt-4-turbo-2024-04-09, at the beginning of April 2024.

GPT-4 Turbo has a 128,000-token context window, equivalent to 300 pages of text in a single prompt, according to OpenAI. The model also has training data knowledge up to December 2023. 

Also: GPT-4 Turbo reclaims the 'best AI model' crown from Anthropic's Claude 3

Compared to the January 2024 version of GPT-4 Turbo, OpenAI says the updated version performs better on a series of benchmarks used to test the proficiency of AI models, including MMLU (Measuring Massive Multitask Language Understanding), MATH (Measuring Mathematical Problem Solving With the MATH Dataset), and GPQA (A Graduate-Level Google-Proof Q&A Benchmark). 

When referring to the updated version of GPT-4 Turbo, OpenAI CEO Sam Altman said that GPT-4 is "now significantly smarter and more pleasant to use," as seen below. 

Where can I access GPT-4/GPT-4 Turbo?

As of May 23, the latest version of GPT-4 Turbo is accessible to users in ChatGPT Plus. The ChatGPT Plus subscription costs $20 per month. When using the chatbot, this model appears under the "GPT-4" label because, as mentioned above, it is part of the GPT-4 family of models.

Also: ChatGPT vs. ChatGPT Plus: Is it worth the subscription fee?

Before taking the plunge, you should remember that even with ChatGPT Plus, GPT-4 has a limit of 40 messages every three hours. There is also a free way to access GPT-4 Turbo: Microsoft Copilot

What is GPT-4o?

GPT-4o is OpenAI's latest, fastest, and most advanced flagship model, launched in May 2024. The "o" stands for omni, referring to the model's multimodal capabilities, which allow it to understand text, audio, image, and video inputs and output text, audio, and images.

Also: 6 ways OpenAI just supercharged ChatGPT for free users

The model is 50% cheaper when accessed through the API than GPT-4 Turbo while still matching its English and coding capabilities and outperforming it in non-English languages, vision, and audio understanding -- a big win for developers. 

Where can you access GPT-4o?

GPT-4o is available in both the free version of ChatGPT and ChatGPT Plus. The advantage with ChatGPT Plus, however, is users continue to enjoy five times the capacity available to free users, priority access to GPT-4o, and upgrades, such as the new macOS app. Free users get booted back to GPT-3.5 when GPT-4o is at capacity. ChatGPT Plus is also available to Team users today, with availability for Enterprise users coming soon. 

What is Microsoft Copilot?

Copilot is Microsoft's AI chatbot, formerly known as Bing Chat. It runs on OpenAI's GPT-4 Turbo. You can access Copilot via its standalone website or within the Bing search engine. 

Also: What is Copilot (formerly Bing Chat)? Here's everything you need to know

The chatbot's popularity stems from its access to the internet, multimodal prompts, and footnotes for free.

What model does ChatGPT currently use?

ChatGPT is powered by GPT-4o. However, when at capacity, free ChatGPT users will be forced to use the GPT-3.5 version of the chatbot. 

What is the difference between GPT-4 and GPT-3.5?

The main difference between the models is that GPT-4 is multimodal, meaning it can use image inputs in addition to text, whereas GPT-3.5 can only process text inputs. GPT-4 is more capable in reliability, creativity, and even intelligence, per its better benchmark scores, as seen above.

What is the difference between the three flagship models: GPT-3.5 Turbo, GPT-4 Turbo, and GPT-4o?

OpenAI's flagship models right now, from least to most advanced, are GPT-3.5 Turbo, GPT-4 Turbo, and GPT-4o. The differences include price, speed, context length, inputs, and outputs. OpenAI has a simple chart on its website that summarizes the differences (see below).

Flagship model differences
Screenshot by Sabrina Ortiz/ZDNET

Can GPT-4 get answers wrong?

Yes, like previous GPT models, GPT-4 has limitations and makes mistakes. OpenAI says the model is "not fully reliable (it 'hallucinates' facts and makes reasoning errors)."

Also: ChatGPT Plus users can now add relevant GPTs to their chats - here's how

Despite the warning, OpenAI says GPT-4 hallucinates less often than previous models. In an internal adversarial factuality evaluation, GPT-4 scored 40% higher than GPT-3.5 (see the chart, below).

ChatGPT internal factual evaluation by category
Screenshot by Sabrina Ortiz/ZDNET
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