GPT-3 has been publicly covered in scientific publications. Same as GPT-2, and GPT. Those are all pre-trained models, where GPT is the abbreviation of Generative Pretrained Transformer. Transformers have been invented in 2017 at Google Brain [1].
That source about GPT-4 is nonsense. It claims GPT-4 will have trillions of parameter, and at the same time links to another page which says that it won't be much bigger than GPT-3:
https://www.datacamp.com/blog/what-we-know-gpt4