On 14 March 2023, OpenAI announced their latest model in the GPT family, GPT-4. In the product announcement post for GPT-4, OpenAI wrote:

Following the research path from GPT, GPT-2, and GPT-3, our deep learning approach leverages more data and more computation to create increasingly sophisticated and capable language models.

We spent 6 months making GPT-4 safer and more aligned. GPT-4 is 82% less likely to respond to requests for disallowed content and 40% more likely to produce factual responses than GPT-3.5 on our internal evaluations.

And in the research announcement post, they begin with the following paragraphs:

We’ve created GPT-4, the latest milestone in OpenAI’s effort in scaling up deep learning. GPT-4 is a large multimodal model (accepting image and text inputs, emitting text outputs) that, while less capable than humans in many real-world scenarios, exhibits human-level performance on various professional and academic benchmarks. For example, it passes a simulated bar exam with a score around the top 10% of test takers; in contrast, GPT-3.5’s score was around the bottom 10%. We’ve spent 6 months iteratively aligning GPT-4 using lessons from our adversarial testing program as well as ChatGPT, resulting in our best-ever results (though far from perfect) on factuality, steerability, and refusing to go outside of guardrails.

Over the past two years, we rebuilt our entire deep learning stack and, together with Azure, co-designed a supercomputer from the ground up for our workload. A year ago, we trained GPT-3.5 as a first “test run” of the system. We found and fixed some bugs and improved our theoretical foundations. As a result, our GPT-4 training run was (for us at least!) unprecedentedly stable, becoming our first large model whose training performance we were able to accurately predict ahead of time. As we continue to focus on reliable scaling, we aim to hone our methodology to help us predict and prepare for future capabilities increasingly far in advance—something we view as critical for safety.

For historical context, here is a brief overview and history of OpenAI's GPT systems from the recently resolved Metaculus question When will GPT-4 be announced?:

GPT stands for "Generative Pre-Training" and was introduced in this paper from OpenAI in 2018. On February 14th 2019, OpenAI announced GPT-2, which became famous within the machine learning community for producing surprisingly coherent written text samples. It used 1.5 billion parameters.

On the 28th of May, 2020, OpenAI released GPT-3, a 175 billion parameter model, widely regarded to have impressive language generation abilities, and in Dec 2022, OpenAI released ChatGPT, widely considered to be "GPT-3.5".